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Abstract
Electrochemical fabrication of micro/nanostructured metallic surfaces with superhydrophobicity has recently aroused great attention. However, the origin still remains unclear why smooth hydrophilic metal surfaces become superhydrophobic by making micro/nanostructures without additional surface modifications. In this work, several superhydrophobic micro/nanostructured metal surfaces were prepared by a facile one-step electrodeposition process, including non-noble and noble metals such as copper, nickel, cadmium, zinc, gold, and palladium with (e.g. Cu) or without (e.g. Au) surface oxide films. We demonstrated by SEM and XPS that both hierarchical micro/nanostructures and spontaneous adsorption of airborne hydrocarbons endowed these surfaces with excellent superhydrophobicity. We revealed by XPS that the adsorption of airborne hydrocarbons at the Ar+-etched clean Au surface was rather quick, such that organic contamination can hardly be prevented in practical operation of surface wetting investigation. We also confirmed by XPS that ultraviolet-O3 treatment of the superhydrophobic metal surfaces did not remove the adsorbed hydrocarbons completely, but mainly oxidized them into hydrophilic oxygen-containing organic substances. We hope our findings here shed new light on deeper understanding of superhydrophobicity for micro/nanostructured metal surfaces with and without surface oxide films.
... However, the surface structure of the Ni-Co coating prepared by Khorsand et al. [43] has many pores, which usually displays low mechanical strength, and the treatment time (exposure to air) is also too long, so the structure and process of the coating need to be further optimized when applied to bipolar plates. Liu et al. [45] found that the metallic surfaces prepared by electrodeposition can obtain high hydrophobicity by annealing at 65 • C for 12 h without using low surface energy substances, which can greatly reduce the time of surface treatment and inspire us to apply this process to the surface modification of bipolar plates. It is expected that the treatment strategy of low-temperature annealing may lead to the unique evolution of the properties (especially wettability) of the nickel-based alloy coated bipolar plates, which would have important guiding significance for subsequent modification research. ...
... According to the determination method of metal layer adhesion in GB/T 40262-2021, the adhesion of the prepared coating is grade 5. It is known that Liu et al. [45] prepared a series of metal surfaces with high hydrophobicity by electrodeposition, without using low surface energy substance. It had been proved that the main reason for the high hydrophobicity was the ad-sorption of airborne hydrocarbons, which could reduce the surface energy of metal surfaces. ...
... According to the determination method of metal layer adhesion in GB/T 40262-2021, the adhesion of the prepared coating is grade 5. It is known that Liu et al. [45] prepared a series of metal surfaces with high hydrophobicity by electrodeposition, without using low surface energy substance. It had been proved that the main reason for the high hydrophobicity was the adsorption of airborne hydrocarbons, which could reduce the surface energy of metal surfaces. ...
This study presents the corrosion behavior and surface properties of SS304 modified by electrodeposited nickel–cobalt (Ni–Co) alloy coating with cauliflower-shaped micro/nano structures (Ni–Co/SS304) in the simulated PEMFC cathodic environment. The hydrophobicity of the as-prepared Ni–Co alloy coating can be improved simply by low-temperature annealing. The morphology and composition of the Ni–Co/SS304 were analyzed and characterized by SEM, EDS, XRD, and XPS. The polarization, wettability, and ICR tests were respectively conducted to systemically evaluate the performance of Ni–Co/SS304 in the simulated PEMFC cathode environment. As revealed by the results, the Ni–Co/SS304 can maintain its hydrophobicity under hot-water droplets as high as 80 °C and demonstrates higher conductivity than the bare SS304 substrate before and after polarization (0.6 V vs. SCE, 5 h), which is of great significance to improve the surface hydrophobicity and conductivity of bipolar plates.
... Surface polishing was also not carried out due to the nature of the study since the usage of any abrader will damage or even eliminate the polished surface. Laser etching has been demonstrated to be capable of creating a superhydrophobic all-metal surface even without a coating through the spontaneous adsorption of airborne hydrocarbons on the surface of the freshly made microstructures [20,21,[54][55][56]]. An ultrafast 355-nm wavelength picosecond laser (Ekspla Atlantic 20) was used to create the surface with a microstructure comprised triangular microchannels 25 µm wide and 25-30 µm tall (Fig. 1a), overlaid with evenly distributed spikes ranging from 50 to 250 nm [16]. ...
... This structure results in an increase in the static contact angle to about 150° (Fig. 1b, c) and a reduction in the hysteresis (i.e., the difference between the receding and advancing contact angles) to around 15° [16]. Prior to any abrasion processing, the laser-ablated samples were left in ambient air for 15 days to ensure the formation of the oxide layer and hydrocarbon overlayer [20,21,[54][55][56]. A more detailed analysis of the manufacturing process and its impact on the surface's wetting properties is presented in [16]. ...
The abrasion testing process of topographically modified surfaces is investigated and their mechanical durability and wear characteristics are presented. The primary aim of the study is to demonstrate that a simple abrasion testing process carries a number of subtle complexities which are crucial for getting comparable results—i.e., sample area, abrasion duration, and presence of a microstructure. All of these factors can significantly alter the results of the testing process and have to be considered during comparison with other durability results. This study also demonstrates how topographically modified aluminum structures tend to restore their hydrophobicity after noticeable mechanical damage due to the natural oxidation process, whereas control samples stay in a hydrophilic state. The findings could be applied to improving the performance of wind or steam turbine blades.
Graphical Abstract
... However, there were also some studies reporting that the material became hydrophobic because the surface energy was reduced when the material came into contact with hydrocarbons in the air [41]. Fig. 8 shows the surface composition of the NieCoeCeO 2 /Ni (2 g/L) composite electrode (Sample b) with a contact angle of 124 . ...
... Fig. 8d shows that the C 1s spectrum was divided into two peaks centred at 284.7 eV and 285.4 eV, corresponding to CeC and CeH in the composite electrode [43]. The CeOeC peak appeared at 288.2 eV [41], but hydrocarbons still dominated. For Ce 3 d in CeO 2 , the peaks located at 898.5 eV corresponded to Ce 3d3/2 and those located at 880.2 eV corresponded to Ce 3d5/2, which demonstrated the coexistence of Ce 4þ in CeO 2 [44]. ...
Hydrogen production from water electrolysis with catalysts is a simple, effective, and environmentally friendly way. However, the slow kinetics of the oxygen evolution reaction (OER) directly affects the catalytic efficiency of water electrolysis during hydrogen production. While the high cost of noble metal catalysts limits their engineering applications. Therefore, there is an urgent need to develop an economical and abundant catalyst with efficient OER performance to replace noble metal catalysts to reduce costs. In this work, we propose a method for the preparation of composite catalytic electrodes by magnetically induced jet electrodeposition. Ni–Co–CeO2/Ni composite electrodes with a unique micro-nano structure and a large specific surface area were rapidly obtained through magnetically induced adsorption of nano-mixed particles. It was found that the Ni–Co–CeO2/Ni composite electrode deposited by magnetically induced electrodeposition exhibited a lower overpotential of 301 [email protected] mA/cm² when the nano-mixed particle concentration was 2 g/L, and the corresponding Tafel slope was as low as 43.72 mV/dec. The key parameters of overpotential and Tafel slope reach or even outperform the best noble metal electrode in the industry, indicating that the Ni–Co–CeO2/Ni composite electrode had excellent OER catalytic performance. The study demonstrates that magnetically induced jet electrodeposition provides a new method for the preparation of catalytic electrodes, which has important applications in the electrolysis of water for hydrogen production.
... However, during the study of the hydrophobic metallic surfaces, an unusual feature of spontaneously changing wettability phenomenon has been discovered and the time-dependent wettability has been confirmed [5,6]. For example, Liu et al. reported that a smooth metallic Au surfaces could become hydrophobic merely by introducing micro/nanostructures without any additional surface modification [7]. Zhu et al. prepared sputtered Cu films with micro-square holes exhibiting transitional wettability from hydrophilic to hydrophobic [8]. ...
... In Fig. S2, the Ni 2p spectrum could be resolved with four photoelectron peaks, which consist of Ni 2p3/2, Satellite 3/2, Ni 2p1/2 and Satellite 1/2, the main peaks are assigned to nickel ions with divalent oxidation state, while the satellite peak is normally to confirm the existence of divalent nickel because of the multiple splitting in the energy levels of the transition metals [40]. While for Cu 2p, the Cu 2p 3/2 and Cu 2p 1/2 peaks have been decomposed into several constituent satellite peaks including Cu/Cu + , Cu 2+ , Satellite 3/2 and Satellite 1/2, which can be assigned to Cu/Cu 2 O and CuO species, respectively [7]. Besides, the atomic ratios of different component peaks are also listed in Supplementary Material Table S2 and Table S3. ...
Hydrophobic surfaces and coatings have attracted more and more interest in recent years due to their broad applications in diverse areas. In many cases, a metallic surface would demonstrate a reversible wettability from hydrophilic state to hydrophobic state spontaneously. However, the wetting behavior and hydrophobic mechanism of metallic surfaces are far from clear. In this work, 304 stainless steel (SS) surface and Ni–Cu–P coatings have been chosen to investigate the intrinsic mechanism of the surface wettability transition with the help of X-ray photoelectron spectroscopy (XPS) and ambient air/vacuum storage treatment. The surface topographies, wetting behaviors and surface chemistry were studied systemically. The results showed that the water contact angle (WCA) variation of the as-prepared surfaces changing from hydrophilic state to hydrophobic state is largely associated with the surface specific area. The recovery of water repellency is related to a time constant which mainly depends on the micro-scale surface convolution or surface roughness. Rougher surface tends to accelerate the surface adsorption of airborne hydrocarbon species in the ambient atmosphere, leading to a more intensive WCA increase. The study provides a generic theoretical justification for relevant time-dependent wettability studies.
... Among various semiconductor materials, cadmium-based (CdO), transparent conductive oxide surfaces stand out due to their structural, optical, and electrical properties [15]. The superhydrophobic properties of cadmium-based transparent conductive oxide surfaces are extremely important due to applications such as corrosion inhibition and anti-reflective surfaces [16][17][18]. Different methods have been proposed in the literature for the synthesis of nanostructured particles and cadmium oxide thin films [19][20][21][22][23][24][25]. Besides methods such as sol-gel, CBD, spray pyrolysis, and CVD, SILAR is a simple, low-cost and easy method that can be used to fabricate superhydrophobic CdO surfaces. ...
This study developed mathematical prediction models to predict the RMS roughness value (Rq) and water contact angle (WCA) values of cadmium-based superhydrophobic transparent conductive oxide surfaces. An experimental design approach was used to optimise the process parameters in the SILAR deposition of CdO films. Validation experiments were carried out under selected random conditions to validate the developed mathematical models. The obtained mathematical models not only predicted the roughness and contact angle values with high accuracy but were also used to determine the optimum process parameters to obtain the most effective surface roughness and contact angle. The results indicated that the developed mathematical models can predict the Rq and WCA values of the synthesized transparent conductive oxide surfaces both under optimum conditions and under randomly selected conditions with relative error varying between 0.6 and 4.7%. The Rq and WCA of the most effective cadmium-based superhydrophobic transparent conductive oxide surface synthesised under optimum conditions were measured as to be 189.1 nm and 151.15°, respectively, and were estimated by the developed models to be 193.3 nm and 150.28°, respectively. The closeness of the experimental and predicted values obtained for both models demonstrated the reliability of the developed mathematical models.
... As shown in Fig. 14, the surface of the foil prepared by LAI during the processing process leads to the formation of unsaturated metal atoms and oxygen atoms, these unsaturated atoms and ions provide a large number of polar sites, making the hydrophobicity of the freshly processed metal surface weaker [24,25]. During the aging treatment, the exposed surface of the workpiece is exposed to circulating air, which spontaneously adsorbs hydrocarbons from the air, imparting excellent superhydrophobicity to the copper surface [26]. Over time, the amount of organic compounds adsorbed on the surface of the workpiece gradually increases, resulting in an improvement in its hydrophobicity. ...
Laser ablation imprinting technology involves using laser ablation to induce shock waves in the plasma, replicating microstructures from a mold surface onto the workpiece to form primary microstructures. Simultaneously, the remelt layer formed by laser ablation creates secondary microstructures on the surface. Further modifications such as fluorination and aging treatments alter the chemical composition of the workpiece surface, reducing surface energy to enhance its hydrophobicity. This study investigates the effects of different numbers of impacts, energy densities, and mold cycles on the surface forming results of aluminum foil. At an energy level of 109.5 J/cm², there was no significant difference in the surface forming effect of copper foil subjected to 3 to 7 impacts. Under conditions of 3 laser pulses, when the laser energy is below29 J/cm², the copper foil workpiece cannot form complete multilevel microstructures. Within the range of 45.2–102.5 J/cm², the formation of multilevel microstructures on the copper foil workpiece improves with increasing energy. However, within the range of 109.5—118.4 J/cm², the workpiece experiences damage. The larger the mold cycle, the better the formation of multilevel microstructures produced by laser ablation imprinting. The effects of aging treatment and fluorination treatment on the workpiece were analyzed from three aspects: wettability, surface chemical composition, and surface morphology. The effects of aging treatment and fluorination treatment on the workpiece were analyzed from three aspects: wettability, surface chemical composition, and surface morphology. The experimental results indicate that under conditions where multilevel microstructures are uniformly formed on the workpiece surface, different variables have insignificant effects on the final contact angle.
... They demonstrated that a thin (<200 nm) coating of cerium oxide could create a durable surface with a low hysteresis angle (<5°), which can increase the heat transfer coefficient up to five times. However, some researchers, such as Preston et al. 4 and Liu et al., 5 have argued that hydrocarbon adsorption is the primary factor responsible for enhanced condensation in REOs and noble metals. Utilizing ion implantation, copper alloy layers were created by Qi et al. 6 on a copper substrate, each less than 1-μm thick, resulting in a 20-fold increase in the condensation heat transfer coefficient. ...
The quest for augmenting dropwise condensation heat transfer performance has been the driving force behind the exploration of innovative techniques and approaches to fulfill the desired objective. Mostly, earlier research on dropwise condensation was devoted to study condensation from horizontal tubes and plates but, rarely, addressed dropwise condensation from vertical tubes. An interesting topic of current research in dropwise condensation is to explore the application of Slippery Liquid Infused Porous Surfaces (SLIPSs) to improve the condensation performance. The aforesaid facts are the motivation behind the topics of interest in the present study. In this study, we explore the applicability of semisolid lubricant‐impregnated porous surfaces in enhancing dropwise condensation performance of a vertical condenser tube. The experiments conducted over a wide range of subcooling (5°C ≤ ΔT ≤ 65°C) in saturated steam environment showed significant improvement in condensation heat transfer coefficient of a vertical condenser tube impregnated with semisolid lubricants when compared to bare vertical condenser tube. The highest enhancement is found to be 280% at a subcooling of 40°C. Furthermore, these surfaces proficiently sustain dropwise condensation over a period of 72 hours without compromising heat transfer performance. The devised fabrication method is simpler, more cost‐effective, and less time‐consuming than earlier techniques used for creating SLIPSs. Additionally, an approach based on numerical optimization by a stochastic global optimization technique, namely, Genetic Algorithm, is proposed to retrieve the coefficients and the exponent in the mathematical expression of overall resistance, that is being used to compute the tube‐side dropwise convection heat transfer coefficient.
... In any case, it could be assumed that the oxide film on the asreceived Al is probably different from the oxide film on the polished and laser-ablated Al. At the same time, the hydrocarbons captured from the surrounding air (Ref [45][46][47][48][49] may also be vulnerable to repeated ice adhesion measurements depending on the time gap between the measurements. Measurements repeated multiple times on the same area within a short period of time (shorter than the time to form a new hydrocarbon layer) may also have an impact on the final results. ...
In this work, a shear stress test is used to evaluate the ice adhesion strength on “as received”, polished and micro/nanoengineered hierarchical superhydrophobic aluminium (produced via one-step laser etching) with fixed- and gradient-pitch structures. Due to the potential mismatch between the ice formation area and the wetting gradient length scale, the shear stress test method has been analysed in detail to understand its applicability to topographic gradients, since this could provide misleading results as compared with the application of this method to fixed-pitch topographic structured surfaces. To address this, the influence of the ice-surface contact area, as well as the mould shape and mould material, on the ice adhesion results, was observed for all samples. Moreover, the impact of the direction of the removal force was investigated on the wetting gradients. Key results are that topographically altered surfaces can be hydrophobic, but not icephobic; whereas non-altered surfaces are hydrophilic, but with much lower ice adhesion. Additionally, gradient surfaces were observed to provide hydrophobicity for most areas of the surface, while allowing removal of the ice column at lower forces from certain directions.
... In addition, Al-coated surfaces with micro-nano structures may absorb organic compounds in the air. The spontaneous adsorption of hydrocarbons could modify the coating surface and reduce its surface free energy, making the surface superhydrophobic [67,68]. Figure 9 shows the surface fluorescence effect of the Al-coated wood. ...
A superhydrophobic coating on wood can effectively improve the hydrophobicity and service life of wood. In this study, an Al superhydrophobic nano-coating was constructed on the transversal section of poplar wood by magnetron sputtering based on glow-discharge plasma. The structure, microscopic morphology, surface elements, and hydrophobic properties were characterized and tested. When coated for 20 s, the water contact angle on the sample surface can reach 148.9°. When coated for 30 min, the Al-coated wood had a contact angle of 157.3°, which could maintain excellent superhydrophobic properties for 300 s. The sputtered Al nanoparticles were uniformly distributed on the wood surface and formed nanoclusters. Plenty of voids between the clusters can trap air and block contact between water droplets and the coating, making the coating obtain superhydrophobic properties. When the coating time was 60 min, the characteristic peak of the Al (111) crystal plane appeared at 38.4°, while the intensities of (101), (002), and (040) peaks of cellulose were reduced. In conclusion, magnetron sputtering was used to deposit a superhydrophobic coating on wood without low surface free energy agents. Furthermore, this research provides new inspirations for the physical modification of wood and the construction of superhydrophobic coatings on wood.
... It is worth noting that the intrinsic hydrophobicity (contact angle larger than 90 • ) of all the electrodes should originate from the quick adsorption of hydrocarbons and oxygen from the air [24,25]. As shown in Fig. 5 and Fig. 6, high content of C and O elements were found on the surface of Samples b and c, while the contribution of O from CeO 2 in the nano-mixed particles was very limited (see Ce content in Table 3). ...
... It is noticed that the portion of O=C bonds decreases sharply in the laser texturing process and the vacuum heating treatment because the thermally unstable O=C dandling bond is vulnerable under laser irradiation and high temperature conditions. Peng Liu et al mentioned that the O=C dandling bond can make the surface hydrophilic [47,48], indicating that the elimination of the O=C dandling bond is one of the important reasons for the transition from hydrophilicity to hydrophobicity of the albronze surfaces. Besides, it is found that the Cu 2 O bond increases after the laser texturing process and the vacuum heating treatment. ...
Biofouling leading to clog is one of the severe issues underwater valve components are facing today. Establishing a superhydrophobic barrier against microorganisms for underwater albronze components is hence of great significance. We demonstrate an all-laser route for superhydrophobic albronze surface fabrication and non-contact microbial diagnostics. Laser-textured albronze surfaces with well-defined periodic valleys and crests exhibit excellent superhydrophobicity with a contact angle up to 151 ± 1° and a contact angle hysteresis of 0.9 ± 0.1°, more than twice that of an original albronze surface (66 ± 2°). The theoretical wettability diagram of water droplets on laser-textured albronze surfaces shows that the surface wettability transits from hydrophilicity towards hydrophobicity as the surface undulation level elevated, matching well with the experimental observation. According to surface chemistry analysis, carbonyl groups on the albronze surfaces are extensively eliminated by laser texturing and vacuum heating treatment, which contributes to the wettability transformation. The anti-fouling performance of the laser-textured albronze surfaces was comparatively studied in chalk ash aqueous solution, starch solution, and microbial suspension, respectively. Laser-induced breakdown spectroscopy was applied for non-contact microbial diagnostics. Greatly enhanced resistance to biofouling on laser-textured albronze surfaces was confirmed. An all-laser route for anti-fouling superhydrophobic albronze surface fabrication and non-contact microbial diagnostics show great promise for next-generation underwater equipment upgrade and on-site monitoring.
... Previous reports mentioned metals such as copper and zinc that adsorb hydrocarbons in the air to lower surface energy and create a superhydrophobic surface [35][36][37]. However, few studies report this application on mild steel surfaces. ...
The fabrication of superhydrophobic coatings on mild steel has attracted considerable attention. However, some methods are cumbersome and unsuitable for large-scale preparation, limiting industrial applications. Furthermore, the extensive use of fluorinated compounds to achieve low surface energy is not environmentally friendly. This paper proposed a facile method based on electrodeposition and annealing to prepare mild steel-based superhydrophobic surfaces without chemical modifications. Subsequently, SEM images were analyzed, and it was observed that the plating parameter (current and time) significantly affected surface morphology. At optimum process parameters, a rough surface with a multi-level structure was formed on the plated surface, contributing to superhydrophobic properties. XPS, EDS, and XRD were utilized to analyze surface composition. The results indicated the presence of copper oxides, zinc oxides, and a large number of hydrocarbons on the prepared superhydrophobic surface. These transition metal oxides on the surface adsorbed hydrocarbons in the air during the annealing process, which lowered the surface energy. Combined with the obtained multi-level morphology, a superhydrophobic surface was achieved. Finally, the corrosion behavior was evaluated in 3.5 wt% NaCl solution by AC impedance spectroscopy. Results showed that the obtained superhydrophobic surface, compared with the untreated coating and the steel substrate, showed a substantial improvement in corrosion resistance. A mild steel-based superhydrophobic surface with a contact angle greater than 150 degrees and excellent corrosion resistance was finally obtained. We hope this study will facilitate the industrial preparation of superhydrophobic coatings, especially in marine engineering, since this method does not require complex processes or expensive equipment and does not require fluorinated substances.
... To comprehensively understand the underlying mechanisms of this strategy, we performed XRD, XPS and Raman measurements of the Laser-TiO2 surfaces, as shown in Figure 4. From the XPS results of C 1 s in Figure 4a-c, we easily find that the adsorption of hydrophilic carboxyl -COOH (288.5 eV) happens on all the samples [47], which makes a sharp contrast to the observed absorption of the COOgroup without the varnish of TiO2 (see Figure S3a-c from the Supplementary Materials). Accordingly, the terminal parts of the long chain of amphiphilic hydrocarbon derivatives are no longer allowed to physically adsorb the non-polar saturated alkanes, leading to the unlikely transformation of the superhydrophilic into the hydrophobic on the surface. ...
The acquiring of superhydrophilic surfaces attracts the strong interest in self-cleaning, anti-fogging and anti-icing fields based on the unique features. However, the persistent time of su-perhydrophilic surfaces is still facing a big challenge because of easily adsorbing hydrophobic groups. Here, we propose a strategy to achieve a superhydrophilicity persisting for an unprece-dently long time on sapphire surfaces, by compounding the femtosecond laser-induced hierarchical structures and the subsequent varnish of TiO2. The superhydrophilic effect (with a contact angle of CA = 0°) created by our method can be well prolonged to at least 180 days, even for its storage in air without additional illumination of UV lights. Based on comprehensive investigations, we attribute the underlying mechanisms to the coordination of laser-induced metal ions on the material surface via TiO2 doping, which not only prevents the adsorption of the nonpolar hydrocarbon groups, but also modulates the photo-response properties of TiO2. In addition, further experiments demonstrate the excellent anti-fogging properties of our prepared samples. This investigation provides a new perspective for further enhancing the durability of superhydrophilicity surfaces.
... The presence of adventitious carbon has been widely reported in literature reports on metal/metal oxide surfaces and is expected to contribute toward lowering the surface energy of the samples. 36,39,40 The Cu-SHO surface showed a CA of 155.2 ± 2.3°( Figure 1(j)), indicating superhydrophobic behavior (CA > 150°). The Cu−P samples presented with a hydrophobic behavior (CA > 90°) with a CA of 115.9 ± 2.6° (Figure 1(m)). ...
Meniscus-confined electrodeposition and electrodissolution are a facile maskless approach to generate controlled surface patterns and 3D microstructures. In these processes, the solid-liquid interfacial area confined by the meniscus dictates the zone on which the electrodeposition or the electrodissolution occurs. In this work, we show that the process of electrodeposition or electrodissolution in a meniscus-confined droplet system can lead to dynamic spreading of the meniscus, thereby changing the solid-liquid interfacial area confined by the meniscus. Our results show that the wetting dynamics depends on the applied voltage and the type of interface underneath the droplet, specifically a smooth surface with a homogeneous solid-liquid interface or a superhydrophobic surface with a heterogeneous solid-liquid and liquid-vapor interface. It is found that both electrodissolution and electrodeposition processes induced droplet spreading in the case of a smooth surface with a homogeneous interface. However, a superhydrophobic surface with a heterogeneous interface under the droplet produced nonlinear spreading during electrodissolution and spreading inhibition during electrodeposition. The underlying mechanisms resulting in the observed behavior have been explicated. The dynamic droplet spreading could modify the dimensions of the patterns formed and hence is of immense importance to the meniscus-confined electrochemical micromachining. The findings also provide fundamental insights into the spreading behavior and wetting transitions induced by electrochemical reactions.
... 44,45 On the other hand, airborne hydrocarbons molecules existing everywhere can adsorb on the metallic or their oxidized surface. 46 Such organic pollutants on rough metal surface can strongly reduce high surface energy of the latter. 47 In order to determine a possible mechanism for improving the hydrophobicity of the produced coatings, surface free energy measurements were carried out. ...
Alloys were potentiostatically codeposited from gluconate baths containing zinc, nickel, and manganese chlorides and/or sulfates. The electrodeposits were characterized in terms of their chemical (XRF, EDS) and phase (XRD, ASA) compositions, surface morphology (SEM), wettability (WCA, SFE), and corrosion resistance in neutral and acid media (linear polarization, immersion test). Morphology and composition of the alloys were mainly dependent on deposition potential, while effect of bath speciation was less emphasized. Multiphase ternary alloys were produced only at potentials more negative than -1.5V (Ag/AgCl). Codeposition of the metals was anomalous and run according to instantaneous nucleation model, but at more electronegative potentials and in a presence of chloride ions transition progressive-instantaneous nucleation stages were observed. Comparison of surface wettability of as-plated and air-stored alloys showed improved (super)hydrophobicity caused by spontaneous oxidation of zinc-rich alloys. Surface free energies of the deposits were discussed. It was found that sulfate anions exhibited distinct effect on cathodic processes demonstrated by higher deposit masses, lower manganese percentages in the alloys, formation of more coarse and compact hydrophobic deposits of high corrosion resistance in neutral solution.
... The hydrophilic component of the fresh E@SSM is 21.1% and the hydrophobic component is 78.9% (Fig. 7d), while the hydrophilic component of the E@SSM stored for 15 days is reduced to 18.7% and the hydrophobic component is increased to 81.3% (Fig. 7e). The reason for the increase in the hydrophobic component may be that the organic hydrocarbons in the air are adsorbed on the surface of the coating, which partly results in the loss of superhydrophilicity of the E@SSM [50,51]. Besides, the roughness of the E@SSM changed from 52 nm to 67 nm (Fig. S13), and the AFM test results showed that the roughness of the E@SSM changed little before and after storage, which was consistent with the previous research results [51]. ...
A superhydrophilic/underwater superoleophobic composite coating ([email protected]) was fabricated through etching and subsequent modification of stainless steel mesh (SSM). It had a water contact angle of 0° in the air, an oleophobic angle of 162.7° underwater, and a sliding angle of 5°. Even after 15 days, the separation efficiency of crude oil-water was up to 98.6% and had a high water flux of 13,535 L m⁻² h⁻¹. After 50 sandy impacts, the [email protected] had an oil contact angle of 158.5° and sliding angles of 13° underwater. Experimental results show that the water flux and the contact angle were closely related, and there was a negative correlation between the water flux and the water contact angle. Furthermore, the [email protected] was featured with long-term stability, chemical stability and excellent mechanical stability. Apart from that, it has potential application value in the field of oil and water treatment.
... Similar observations are reported on aluminium [64,65], aluminium alloys [66,67] and other alloys [68]. Not only the laser patterning but also surface preparation techniques such as polishing/micro grooving [69], electro-deposition [70,71], thermal oxidation [72], solution precursor plasma spray process [73], lithography followed by sputtering [74] also shown to affect the superhydrophobicity with time. The time-dependent transition from hydrophilicity to hydrophobicity was attributed to the volatile organic compounds accumulated on the surface during storage in ambient conditions. ...
Superhydrophobic titanium surfaces with different line spacing (pitch) of 20, 50, 80 and 100 μm are fabricated using nanosecond laser patterning and their antibiofouling, superhydrophobicity, abrasion resistance and self-cleaning properties are studied. The surface morphology, surface profiles and surface roughness are obtained from scanning electron microscopy (SEM), optical microscopy and surface profilometry. Initially, the dual scale roughness structured laser patterned surfaces were hydrophilic but on prolonged storage time in ambient conditions, average water contact angle (WCA) > 160° was obtained due to the accumulation of atmospheric hydrocarbon compounds on the surface which was confirmed by laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). The laser patterned titanium samples exposed to the Pseudomonas sp., bacterial culture showed a 4-order reduction in bacterial adhesion as compared to control samples. Furthermore, the superhydrophobic laser patterned samples exhibited excellent water repellency at different ionic strength chloride solutions, photo-catalytic activity under visible light and abrasion resistance. The laser patterned titanium samples are found to regain the superhydrophobicity by replenishing the carbonaceous layer (denuded in organic solvents) on exposure to an open atmosphere for 14 days. This study provides new avenues to engineer the wetting properties of surfaces by varying laser patterning conditions.
... One of the most common methods to improve the tribological properties of the surfaces of micro-components is the surface modification technology, such as anodization [7], electrodeposition [8], plasma spraying [9], chemical vapor deposition [10], and physical vapor deposition [11]. However, traditional lubrication methods cannot meet the requirements of practical application environments due to the limited size of micro-components in the application in MEMS. ...
Self-assembled monolayers (SAMs) are considered as the potential lubricants and can be used to control the adhesion and the wear in micro-electromechanical system. In this study, alkanethiols SAMs of single component and mixed alkanethiols SAMs with different alkyl chain lengths were fabricated on the surfaces of nickel (Ni) substrates by the solution deposition method. The surface morphology and the wetting property of bare Ni substrate and different SAMs were characterized by the atomic force microscopy and water contact angle measurement. Moreover, a ball-on-plate tribometer was selected to measure the tribological properties of bare Ni substrate and different SAMs. The surface free energy of Ni Substrate decreased significantly after the surface modified by different alkanethiols molecules, which effectively reduced the surface adhesion of Ni substrate. The friction coefficients of Ni substrates coated with different SAMs were much lower than that of bare Ni substrate. In addition, the mixed alkanethiols SAMs had the greatest lubricity and wear resistance compared to other alkanethiols SAMs of single component.
... Moreover, functional super-hydrophobic MS with high stability and reusability as well as excellent selectivity are worthy of further study [30]. Recently, it has been reported that superhydrophobic pure metal surfaces can be prepared by hydrophobic methods without the functionalization of hydrophobic molecules [31][32][33]. Under heating conditions, the surface energy of metals can be effectively reduced by spontaneous adsorption of carbon pollutants; it may provide a new, low-cost green pathway to fabricate superhydrophobic MS, without using any additional low surface energy materials. ...
Melamine sponge (MS) has the characteristics of multilayer network structure, high porosity, adjustable pore structure, and low price, which is considered to be an ideal material for oil leakage treatment. Here, a facile, economical, environmental friendly, and one step reaction was developed to fabricate Ag nanoparticles (NPs) decorated MS composite with tannic acid (TA) as a reducing agent. By reduction reaction, the super-hydrophobic and super-oleophylic surface of the MS–TA–Ag composite was formed, demonstrating a single selectivity for oil and water. Thus, the adsorption capacity of MS–TA–Ag composites for various oils/organic solvents can reach 48~129 times its own weight and and display superior efficiency to separate oil/organic solvent from the water. In addition, the MS–TA–Ag composite has stable super-hydrophobicity and reusability. It is exciting that modified MS exhibits excellent chemical stability properties after a long processing time with strong alkali, strong acids, and salt solutions. The simple strategy provides a method for the preparation of large-scale oil spill cleaning and recovery materials.
... The oxidation of nickel exposure to air produces a hydrophobic NiO, causing some wettability changes [120]. Perhaps, hydrocarbons in the air may reduce the surface energy, contaminating the coating [121] The coating showed a perfect anti-corrosion performance with corrosion potential and corrosion current density to be −0.237 V and 0.06 μA/cm 2 , and measurements were done in 3.5% NaCl solution showing a potentiodynamic polarization curve. ...
The traditional hydrophilic-hydrophobic conversion methods have the disadvantages of the introduction elements, long time, and complex operation. In this paper, the hydrophilic-hydrophobic conversion was achieved on the surface of 316L stainless steel using electron beam irradiation (EBI) combined with low-temperature oxidation. The results demonstrated that EBI improved the contact angle from 89° to 135°. The contents of C-C/C-H hydrophobic functional groups were found to be notably increased by low electron doses in the experiments. The contents of C-O-C, O-C = O, and -OH hydrophilic functional groups decreased. The interaction of excited secondary electrons with precursor molecules generated free radical fragments that adsorbed onto surfaces and formed new chemical bonds, changing the content of the functional groups. After low-temperature oxidation, the contact angle decreased to 76°. Following a second EBI, the contact angle increased to 144°. Due to the reversible changes in the C-C/C-H, C-O-C, and O-C = O group contents, the hydrophilic-hydrophobic conversion was achieved without introducing new elements during the whole process.
Generally, fabricating bionic superhydrophobic surfaces on hydrophilic smooth materials involves preapring micro/nanostructures and chemical modification. Recent breakthroughs based on organic adsorbate on hierarchically structured surfaces for superhydrophobicity are very promising...
Green fabrication of superhydrophobic surface by water‐based processing is still challenging, because introduction of the substances with hydrophilic moieties compromises its superhydrophobicity. Herein, a plasmon‐driven photochemical reduction reaction under ultraviolet light (UVA) irradiation is first discovered and is applied to deoxygenation of hydrophilic organic adsorbates on rough nano‐Ag coating for the formation of stable superhydrophobic surface. A nano‐Ag coating with strong localized surface plasmon resonance in the UVA region is prepared by a water‐based silver mirror reaction and results in a unique chemical reduction reaction on its surface. Consequently, the low residual hydrophilic functionalities and the formed cross‐linked structure of the adsorbate on Ag nanoparticles (NPs) enables the coating to exhibit stable superhydrophobicity against to both air and water. The superhydrophobic Ag NP‐coated sandpaper can also be used as a surface‐enhanced Raman scattering (SERS) substrate to concentrate aqueous analytes for trace detection.
Scaling is a universal issue encountered in pipeline steel during offshore oil extraction. In this paper, a synergic anti-scaling Cu-Zn-CeO2 coating on the pipeline steel substrate was fabricated by one-step composite electrodeposition and magnetic stirring. It shows the wettability transition from superhydrophilic to superhydrophobic of the multi-scale structured Cu-Zn-CeO2 coating without low-surface-energy modification after heating at 60℃ for 60 min and stored in air for ∼ 35 days. The wettability transition is owing to the hydrocarbons adsorption. The heating treatment and the multi-scale structure improve the hydrocarbons adsorption and reduce the transition time. The inherent hydrophobic CeO2 is beneficial for the superhydrophobic property and reduces the transition time. Compared with the steel substrate and previous superhydrophobic Cu and Cu-Zn coatings, it indicates the superhydrophobic Cu-Zn-CeO2 coating shows the promising synergic anti-scaling property due to its superhydrophobicity and the anti-scaling property of Cu-Zn alloys. This eco-friendly synergic anti-scaling Cu-Zn-CeO2 coating also shows excellent self-cleaning and anti-fouling properties. Moreover, the stability of the superhydrophobic Cu-Zn-CeO2 coating was enhanced compared with our previous superhydrophobic Cu-Zn coating due to CeO2 nanoparticles. This research enriches the theory and the technology of the wetting field, which also provides a technical basis for solving scaling problems of pipelines.
In the present work, the coating surface subjected to heating in a vacuum drying oven without additional artificial modification exhibited a spontaneous change in its wettability from superhydrophilicity to superhydrophobicity. To clarify the mechanism of wettability transition and reveal the role of vacuum heating, plasma-sprayed metallic coatings with optimized biomimetic micro–nano-multiscale structure were taken as the research subjects. The influence of surface chemical composition on the wettability of coatings was emphatically studied via infrared spectroscopy and x-ray photoelectron spectroscopy. According to the results, the main reason for the wettability transition was the change in chemical state of the coating surface due to spontaneous adsorption of alkanes and alkyl chains with low surface free energy from the vacuum residual gas during vacuum heating. Heating promoted desorption of the initial physical adsorption layer and subsequent re-adsorption of residual gas, and vacuum system supplied the adsorbates, thereby providing the driving force for the spontaneous adsorption. The increase in heating temperature could promote re-adsorption of residual gas and improve the transition degree of wettability. The prepared superhydrophobic coatings had an excellent self-cleaning property. Therefore, this study not only opens up new prospects for rapidly achieving superhydrophobicity of surfaces, but also reveals the strong effect of vacuum drying on the surface wettability.
In this study, La-doped diamond-like carbon (DLC) films were prepared by magnetron co-sputtering of individual graphite and La targets. The mechanical properties and surface wettability of the DLC films were investigated in terms of the evolutions of microstructures and chemical compositions with La content. The results revealed that the doped La dissolved into the DLC films working as a catalyst made them smoother and locally graphitized. Moreover, a different dependency of residual stress upon sp³-C fraction to that of hardness and elastic modulus was found in the DLC films. Further, the air-exposed DLC films suffered from a series of surface physical/chemical reactions with air molecules and ubiquitous volatile organic compounds (VOCs), accompanied by brilliant and quick color evolutions over initial time, which dominated the time-dependent surface wettability. Finally, the doping-induced enhancements of both VOCs adsorption and sp²-C fraction contributed to the surface wettability transition from the intrinsic hydrophilicity to desired hydrophobicity of the DLC film. This study demonstrated here aims to expose the complex microstructures and related properties of DLC films with La doping, and offer a feasible method of preparing high-performance DLC films with low residual stress and adjustable surface wettability.
Ceria has become a potential candidate for the preparation of superhydrophobic surfaces due to the apparent intrinsic hydrophobicity reported in recent years. In the present study, a CeO2 coating with bi-scale structures imitating lotus leaf surface was deposited by air plasma spraying (APS). It was found that the wettability of the coating surface exhibited a special delayed phenomenon, that the surface needed to be stored in the atmosphere for a period of time before it could change from superhydrophilicity in the fresh as-sprayed state to superhydrophobicity. To elucidate the mechanism, the research focused on analyzing the changes in the chemical composition of the surface. The results showed that adsorption effect was the main factor dominated the surface wettability. During atmospheric storage, the coating surface spontaneously adsorbed low surface free energy substances, mainly carboxylates containing alkane chain and alkanes, resulting in the transition of wettability. The bombardment of argon plasma jet to ceria during APS led to the valence state change of Ce atoms, resulting in the generation of coordinatively unsaturated metal cations acted as active adsorption sites, which was the reason for the spontaneous adsorption. Due to the restrictions on the location of the active sites and the limited concentration of airborne adsorbates, the spontaneous adsorption proceeded slowly, which led to the retardation of superhydrophobicity for the coating surface. The study laid a theoretical foundation for the preparation of CeO2 superhydrophobic coatings by APS, and provided further insights into the underlying mechanism of the apparent hydrophobicity of CeO2.
The Cu meshes with reversible super-wettability have multifunctions of self-cleaning, oil-water separation, floating-oil collection and underwater oil lossless-transportation. However, the facile method to tune the surface wettability and prepare reversibly super-wetting Cu meshes remains a great challenge. In this work, one-step chemical-etching method was used to construct the hierarchically-structured CuO of nano-sheets and micro-clusters on Cu meshes to provide suitable surface roughness essential for super-wettability. The surface wettability of Cu mesh was then facilely tuned by controlling the adsorption and desorption of C-containing species at the Cu mesh surface through C-rich ambience storage and IR irradiation for short duration. The super-wetting transition of Cu meshes between superhydrophobicity/superoleophilicity and superhydrophilicity/underwater-superoleophobicity could repeat for many cycles. Moreover, the super-wetting Cu meshes demonstrated excellent mechanical, physical and chemical stabilities. The switchable super-wettability endowed the Cu meshes with integrated multi-functions, which demonstrated remarkable performance of self-cleaning, oil-water separation, floating-oil collection and underwater oil lossless-transportation. This study suggests that utilizing C-rich ambience storage and IR irradiation to control the content of C-containing species at the Cu mesh surface is a facile and effective way to tune the surface wettability of Cu meshes, which can be easily extended to realize super-wettability transition of various materials.
A novel superhydrophobic Ni-graphene coating was synthesized by one-step electrodeposition without low surface energy modification. The two-dimensional and three-dimensional morphology were investigated by scanning electron microscope, atomic force microscope, and confocal profilometry. Combining fractal theory and power spectral density analysis, the structural characteristics of the coating surface were quantified by key surface parameters. By building the numerical relationship between surface structure and wetting property, the coating-water contact mode was identified according to the measured contact angle and fractal contact angles calculated from Cassie and Wenzel theories. Additionally, the optimized deposition parameters and the role of graphene on the coating structure were also pinpointed. The results show that the Ni-graphene coating deposited at graphene oxide concentration of 0.20 g·L⁻¹ and deposition current density of 40 mA·cm⁻² exhibited dual-level fractal structure in micro- and nano-scales. The Ni-graphene superhydrophobic coating possessed a water contact angle of 156.1°±0.6°, a sliding angle of 6.2°±0.8°, as well as self-cleaning characteristics, and the wetting system was confirmed to follow the Cassie contact mode.
Driven by the overuse of antibiotics, pathogenic infections, dominated by the rapid emergence of antibiotic resistant bacteria, have become one of the greatest current global health challenges. Thus, there is an urgent need to explore novel strategies that integrate multiple antibacterial modes to deal with bacterial infections. In this work, a Co(Ni,Ag)/Fe(Al,Cr)2O4 composite duplex coating was fabricated using template-free sputtering deposition technology. The phase constitution of the coating was estimated to be 79 wt % Fe(Al,Cr)2O4 phase and 21 wt % of an Ag-containing metallic phase. The composite coating consisted of a ∼10 μm-thick porous outer-layer and a ∼6 μm-thick compact inner-layer, in which the outer-layer is composed of a densely stacked array of microscale cones. After exposure to ambient air for 14 days, the composite coating showed a wettability transition from a superhydrophilic nature to exhibit adhesive superhydrophobic behavior with a water contact angle of 142° ± 2.8°, but it reverted to its initial superhydrophilic state after annealing in air at 200 °C for 5 h. The absorption rate of the as-received composite coating exceeds 99% in a broad band spanning both the visible and NIR regions and showed a high photothermal efficiency to convert photon energy into heat. Similarly, the composite coating showed microwave absorption behavior with a minimum reflection loss value of 38 dB at 4.4 GHz. In vitro antibacterial tests were used to determine the antibacterial behavior of the composite coating against Escherichia coli and Staphylococcus aureus after 60 min of visible light irradiation. After this exposure, the as-prepared composite coating exhibited nearly 100% bactericidal efficiency against these bacteria. The antibacterial behavior of the coating was attributed to the synergistic effects of the superhydrophilic surface, the release of Ag+ ions, and the photothermal effect. Therefore, this composite coating may be a promising candidate to efficiently combat medical device-associated infections.
In this work, Ni–Mo–SiC–TiN nanocomposite coatings were deposited on aluminium alloy by pulse electrodeposition with various electrodeposition parameters. The influences of the pulse frequency and duty cycle on the phase structure, morphology, mechanical and corrosion performance of the coatings were systematically investigated. The results showed that with increasing pulse frequency and decreasing duty cycle, the content of embedded duplex nanoparticles increased, and the grains refined gradually. The nanocomposite coating that was prepared at 20% duty cycle and 1000 Hz pulse frequency exhibited compact, uniform, and fine microstructures with the maximum incorporation of nanoparticles (6.81 wt% TiN and 1.72 wt% SiC). The wear rate and average friction coefficient then declined to 4.812 × 10⁻⁴ mm³/N·m and 0.13, respectively, with a maximum microhardness of 519 HV. Simultaneously, the corrosion current density was reduced to 3.11 μA/cm², and a maximum impedance of 34888 Ω cm² was exhibited. The uniformly distributed duplex nanoparticles acted as a hindrance, which consequently supported the enhancement of corrosion and wear resistance. By investigating the variation of the pulse diffusion layer with electrical parameters, it was discovered that when the crystallite size is equivalent to or smaller than the diffusion layer thickness, it would be easier to cross the diffusion layer to incorporate in the coating. Additionally, the effects of various duty cycles and pulse frequencies on the nucleation process of the grains were discussed.
Nickel coatings with different surface characteristics were prepared on copper substrate by electrodeposition. Subsequently, the as-coating surface was etched with a mixed solution of FeCl3, HCl and H2O2 at different times, to obtain different surface morphologies and special microstructures. The surface morphologies, element composition, roughness and liquid contact angle were characterized by scanning electron microscope, energy dispersive X-Ray spectroscopy, 3D digital microscope and contact angle measurement. The van Oss-Chaudhury-Good method was used to calculate the solid surface free energy and discuss the variation of surface wettability. The results show that etching time has a significant effect on surface morphology, roughness and wettability. After long-time physical aging, the multiple polygonal-layered architectures and larger-sized layered microstructure can maintain high surface free energy and keep the liquid metal in a good hydrophilic state, which provides a reference for optimizing the surface morphologies of the casting roll. This will improve the heat transfer efficiency and promote heterogeneous nucleation during twin-roll continuous casting.
A method for fabricating superhydrophobic stainless-steel meshes based on magnetic field-assisted jet electrodeposition is proposed. Ferromagnetic nickel particles (Nip) were added to the electroplating solution to prepare Ni/Nip coatings with mountain-like rough structure on stainless-steel meshes, followed by application of a parallel magnetic field in the cathode region. Magnetic fields play an indispensable role in the preparation of coatings. Exposure to air for 6 days resulted in a spontaneous switch of the coating from superhydrophilicity to superhydrophobicity and exhibited superoleophilicity. X-ray photoelectron spectroscopy revealed that this transition in wettability was related to spontaneous adsorption of hydrocarbons in the air induced by the coating. Based on the superhydrophobicity and superoleophilicity of the as-prepared Ni/Nip-coated meshes, high-efficiency, high-throughput, and high-purity separation of oil-water mixtures was achieved with a 300-mesh mesh. Furthermore, the as-prepared meshes continue to exhibit a separation efficiency greater than 97.0% and stable reusability even after 50 repeated separations.
Some experimental studies have proven that micro/nano structured coatings achieve superhydrophobicity in air, without low-energy modification. However, it remains an issue how comprehensively explain the reason for changes in wettability. Herein, a hierarchically (nano-submicron-micro) structured Cu coating was fabricated on pipeline steel substrate by one-step electrodeposition. Notably, the superhydrophilic hierarchically structured Cu coating transforms to superhydrophobicity after stored in air for 15 days without chemical modification, with water contact angle of 151° and roll off angle of 3°. Both the microstructure and the chemical composition were characterized to understand the wettability transition mechanism. The fresh hierarchically structured Cu coating exists various defects, with high surface energy, which lead to superhydrophilicity. After the Cu coating stored in air, hydroxylation contributes to hydrocarbons adsorption, resulting in superhydrophobicity. The adsorption kinetic curve model shows that the hierarchical structure promotes hydrocarbon adsorption, which prominently reduces the transition time from superhydrophilicity to superhydrophobicity. The three-level wetting model is constructed to analyze the wetting state when water contacts the Cu coating, which verifies that it is the stable Wenzel-Cassie-Cassie wetting state. Moreover, the superhydrophobic Cu coating maintained anti-scaling property after immersing at 70 °C for 4 h. The anti-scaling behavior and mechanism of the superhydrophobic Cu coating were analyzed by both nucleation and wetting theories. The Cu coating also shows excellent self-cleaning property, water droplet impact resistance, and chemical stability. The superhydrophobicity of the Cu coating also maintained in weak acid and base solutions for 12 min. This study enriches and develops the theory and the technology in the field of wetting, and provides technical support and theoretical basis for the development of superhydrophobicity without low-energy modification.
Surface‐enhanced Raman scattering (SERS) is considered a promising analytical technique for the detection of analytes. Considering the practical SERS detection, it is necessary to develop low‐cost, highly sensitive, and recyclable SERS‐active substrates. Here, a simple and flexible approach is proposed to fabricate a superhydrophobic Ag‐decorated CuO (named as CuO@Ag) nanowire array substrate with analyte‐concentrating and self‐cleaning binary functions for ultrasensitive and recyclable SERS detection. During this process, a superhydrophobic CuO@Ag nanowire array is made via fabrication of a CuO nanowire array by oxidizing and calcinating an ordered porous anodic aluminum oxide template on Cu foil, and following with Ag sputtering deposition on CuO nanowire array. Remarkably, this SERS substrate exhibits ultrasensitive SERS detection ability attributed to superhydrophobic plasmonic metal nanostructured arrays with high analyte‐concentrating ability and excellent photocatalytic capability due to this metal‐semiconductor composite nanostructure. These advantageous properties allow for SERS detection of malachite green with a limit of detection of 6.73 × 10−13 m and self‐cleaning via photodegradation of adsorbed analytes with visible‐light illumination. Consequently, it achieves recyclable SERS detection. This research demonstrates a simple and flexible approach for fabricating recyclable SERS‐active substrate, which expands the practical SERS applications in chemical and biological analysis, food safety, and healthcare. Superhydrophobic CuO@Ag nanowire array substrate with analyte‐concentrating and self‐cleaning binary functions is prepared via an anodic aluminum oxide template‐assisted chemical oxidation reaction combined with calcination dehydration process and Ag sputtering deposition, which can serve as a visible‐light‐driven photocatalytic surface‐enhanced Raman scattering (SERS) platform for ultrasensitive and recyclable SERS detection.
A simple method was proposed to prepare conductive and superhydrophobic copper‑carbon nanotubes (Cu-CNTs) composite coatings on ABS (acrylonitrile-butadiene-styrene copolymers) substrate. In this work, we investigated the variation of wettability and chemical composition when the prepared coatings were stored in the air. The freshly prepared superhydrophilic Cu-CNTs composite coatings adsorbed the airborne hydrocarbons and switched to superhydrophobicity after being exposed in the air for two weeks. Meanwhile, the coatings prepared at 1 A dm⁻² presented good superhydrophobicity (water contact angle ~158.4°, water roll-off angle ~5.3°) and conductivity (0.126 Ω sq.⁻¹). The superhydrophobicity of the coatings was attributed to the lamellar micro-nano structures and the spontaneous adsorption of low free energy airborne hydrocarbons. What is more, the coatings showed good droplets impact stability, self-cleaning performance, and self-recovering ability to resist damage in practical applications.
A simple one-step anodizing process is developed for the large-scale preparation of the tremella-like Cux[email protected]xS nanosheet films on Cu mesh, and the prepared organic-free Cux[email protected]xS nanosheet films on Cu mesh exhibit excellent mechanical stability and corrosion resistance. The fresh organic-free tremella-like Cux[email protected]xS nanosheets have the superhydrophilicity and underwater superoleophobicity. But after storage in atmosphere for about 6 days under room temperature, the wettability is gradually transformed into superhydrophobicity and superlipophilicity. Importantly, the wettability can turn back again to the superhydrophilicity and underwater superoleophobicity after the annealing process at 200 ℃ in air environment. So the stable reversible wetting transition is realized, then the transition mechanism has been investigated by the detailed X-ray photoelectron spectroscopy (XPS) characterization, and is mainly attributed to the production of hydroxide radicals and adsorption of C-C/C-H species on the Cux[email protected]xS nanosheet surface. Lastly, the prepared tremella-like Cux[email protected]xS nanosheets on copper mesh have been successfully applied for on-demand oil/water separation with high efficiency.
In this article, nickel (Ni) coating was constructed on brass substrate by a simple electrodeposition technique, and myristic acid/TiO2 composite (MTC) modifier was used to modify Ni coating. The chemical composition and surface morphology of MTC confirm that myristic acid (MA) was successfully grafted on TiO2 nanoparticles. As a comparison, the structures of the Ni coatings were modified by MTC or MA. We found that both modified Ni coatings exhibit strong durability, self-cleaning and superhydrophobicity ability and have good prospect of decontamination. After Ni coating had been modified by MTC, the water contact angle and sliding angle of MTC-Ni were > 170° and < 5°, respectively. In addition, the MTC-Ni coating shows improved corrosion resistance, which can effectively retard the corrosion of brass. This novel and facile electrodeposition-modification route is believed to be widely applied to preparing superhydrophobic surfaces on metallic materials.
Cellulosic materials are widely used in daily life for paper products and clothing as well as for emerging applications in sustainable packaging and inexpensive medical diagnostics. Cellulose has a high density of hydroxyl groups that create strong intra- and interfiber hydrogen bonding. These abundant hydroxyl groups also make cellulose superhydrophilic. Schemes for hydrophobization and spatially selective hydrophobization of cellulosic materials can expand the application space for cellulose. Cellulose is often hydrophobized through wet chemistry surface modification methods. This work reports a new modification method using a combination of atomic layer deposition (ALD) and atmospheric heating to alter the wettability of purely cellulosic chromatography paper. We find that once the cellulosic paper is coated with a single ALD cycle (1cy-ALD) of Al2O3, it can be made sticky superhydrophobic after a 150 °C ambient post-ALD heating step. An X-ray photoelectron spectroscopy investigation reveals that the ALD-modified cellulosic surface becomes more susceptible to adsorption of adventitious carbon upon heating than an untreated cellulosic surface. This conclusion is further supported by the ability to use alternating air plasma and heat treatments to reversibly transition between the hydrophilic and hydrophobic states. We attribute the apparent abruptness of this wetting transition to a Cassie-Wenzel-like phenomenon, which is also consistent with the sticky hydrophobic wetting behavior. Using scanning probe methods, we show that the surfaces have roughness at multiple length scales. Using a Cassie-Wenzel model, we show how a small change in the surface's Young's contact angle-upon adsorption of adventitious carbon-can lead to an abrupt increase in hydrophobicity for surfaces with such roughnesses. Finally, we demonstrate the ability to spatially pattern the wettability on these 1cy-ALD-treated cellulosic papers via selective heating. This ALD-treated hydrophobic paper also shows promise for microliter droplet manipulation and patterned lab-on-paper devices.
In the present work, a novel and fast fabrication method was proposed to modify the surface of hardened cement paste (HCP) imparting superhydrophobic properties. Sodium laurate was selected as the modifier among the 6 kinds of sodium carboxylates because of its good water solubility and remarkable hydrophobic modification effect. After immersing in the aqueous solution of sodium laurate at room temperature for only 5 s, the ordinary Portland cement-based HCP surface exhibits superhydrophobicity, with a water contact angle (CA) of 154.3° and a sliding angle of 8.7°. Colored superhydrophobic HCP can be prepared by using pigments or dyes to give the HCP surface a decorative effect. The aqueous solution of sodium laurate also imparts the superhydrophobic modification to the HCPs of aluminous cement and sulfoaluminous cement. Additionally, using the method of “cement coating + surface treatment”, the non-cement-based substrates can also be modified into a superhydrophobic surface with sodium laurate, thereby expanding the application range of this method. Furthermore, due to the extremely fast preparation speed, when the surface of HCP is damaged, its superhydrophobicity can be quickly repaired. After superhydrophobic modification, the capillary water absorption coefficient and water absorption rate of the HCPs decreased by 63.81% and 97.77% respectively in comparison with the pristine HCPs. Such easy fabrication, low cost, environmentally friendly, and easy repairable superhydrophobic surfaces have potential applications in the field of building materials such as rendering mortars with self-cleaning functions and colorful decorative effects.
It has been expected that superhydrophobic (SHP) surfaces could have potential anti-icing applications due to their excellent water-repellence properties. However, a thorough understanding on the anti-icing performance of such surfaces has never been reported; even systematic characterizations on icing behavior of various surfaces are still rare because of the lack of powerful instrumentations. In this study, we employed the electrochemical anodic oxidation and chemical etching methods to simplify the fabrication procedures for SHP surfaces on the aluminum alloy substrates, aiming at the anti-icing properties of SHP surfaces of various engineering materials. We found that the one-step chemical etching with FeCl3 and HCl as the etchants was the most effective for ideal SHP surfaces with a large contact angle (CA, 159.1°) and a small contact angle hysteresis (CAH, 4.0°). To systematically investigate the anti-icing behavior of the prepared SHP surfaces, we designed a robust apparatus with a real-time control system based on the two stage refrigerating method. This system can monitor the humidity, pressure, and temperature during the icing process on the surfaces. We demonstrated that the SHP surfaces exhibited excellent anti-icing properties, i.e., from the room temperature of 16.0 °C, the icing time on SHP surfaces can be postponed from 406s to 676s compared to the normal aluminum alloy surface if the surfaces were put horizontally, and the icing temperature can be decreased from −2.2 °C to −6.1 °C. If such surfaces were tilted, the sprayed water droplets on the normal surfaces iced up at the temperature of −3.9 °C, but bounced off the SHP surface even as the temperature reached as low as −8.0 °C. The present study therefore suggests a general, simple, and low-cost methodology for the promising anti-icing applications in various engineering materials and different fields (e.g., power lines and aircrafts).
This review article summarizes the key areas of self-cleaning coatings, primarily focusing on various materials that are widely used in recent research and also in commercial applications. The scope of this article orbits around hydrophobic and hydrophilic coatings, their working mechanism, fabrication techniques that enable the development of such coatings, various functions like Anti-icing, Electro-wetting, Surface switchability and the areas where selfcleaning technology can be implemented. Moreover, different characterization techniques and material testing feasibilities are also analyzed and discussed. Though several companies have commercialized a few products based on self-cleaning coating technology, much potential still remains in this field.
It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.
Temperature programmed desorption (TPD) and X-Ray photoelectron spectroscopy (XPS) studies on clean polycrystalline graphite under ultra high vacuum conditions are described. The same three strongly bound oxygenated species are formed after O2, CO2 and H2O adsorption. They decompose to give CO at 973, 1093 and 1253 K. Small amounts of CO2 are also produced after adsorption of these gases, with desorption temperatures at 463, 573, 693, 793 and 793 K. Attempts are made to ascribe these TPD features more precisely. After H2O adsorption, some H2 is evolved at ca. 1300 K. Hydrocarbons (C1–C6) are also produced but in smaller amounts. A general mechanism is proposed for the gasification reactions of graphite with O2, CO2 and H2O. Physical wetting of the clean graphite surface leads to a H2O molecule reversibly bound to the carbon surface. According to XPS data, a hydrate type of bond is proposed. Considerations on the noncatalytic as well as on the catalytic steam gasification of graphite are made. It is suggested that in both cases the reaction is not only controlled by the desorption of the products (i.e., the decomposition of the surface intermediates) but also by the sticking probability of the H2O on the graphite edges.
Superhydrophobic and superhydrophilic properties of chemically-modified graphene have been achieved in larger-area vertically aligned few-layer graphene nanosheets (FLGs), prepared on Si (111) substrate by microwave plasma chemical vapor deposition (MPCVD). Furthermore, in order to enhance wettability, silicon wafers with microstructures were fabricated, on which graphene nanosheets were grown and modified by a chemical method to form hydrophilic and hydrophobic structures. A superhydrophilic graphene surface (contact angle 0°) and a superhydrophobic graphene surface (contact angle 152.0°) were obtained. The results indicate that the microstructured silicon enhances the hydrophilic and hydrophobic wettabilities significantly.
Primary and secondary contributions to ambient levels of volatile organic compounds (VOCs) and aerosol organic carbon (OC) are determined using measurements at the Pittsburgh Air Quality Study (PAQS) during January-February and July-August 2002. Primary emission ratios for gas and aerosol species are defined by correlation with species of known origin, and contributions from primary and secondary/biogenic sources and from the regional background are then determined. Primary anthropogenic contributions to ambient levels of acetone, methylethylketone, and acetaldehyde were found to be 12-23% in winter and 2-10% in summer. Secondary production plus biogenic emissions accounted for 12-27% of the total mixing ratios for these compounds in winter and 26-34% in summer, with background concentrations accounting for the remainder. Using the same method, we determined that on average 16% of aerosol OC was secondary in origin during winter versus 37% during summer. Factor analysis of the VOC and aerosol data is used to define the dominant source types in the region for both seasons. Local automotive emissions were the strongest contributor to changes in atmospheric VOC concentrations; however, they did not significantly impact the aerosol species included in the factor analysis. We conclude that longer-range transport and industrial emissions were more important sources of aerosol during the study period. The VOC data are also used to characterize the photochemical state of the atmosphere in the region. The total measured OH loss rate was dominated by nonmethane hydrocarbons and CO (76% of the total) in winter and by isoprene, its oxidation products, and oxygenated VOCs (79% of the total) in summer, when production of secondary organic aerosol was highest.
The transition from cellular to dendrite was obtained at the spindle of tip radius by comparing experimental and theoretical study on Al-4%Cu alloy during directional solidification. It was found that the tip radius fell quickly in cellular stage but fell slowly in dendrite stage. The KGT (W. Kurz, B. Giovanola and R. Trivedi) model and non-equilibrium effect were applied to research the tip radius and interface temperature in order to obtain the transitional characteristic from dendrite to cellular. The results indicated that the tip radius and interface temperature were both decreased with increasing withdrawal rate, after reached the critical points, finally turned to rise sharply. It was eventually obtained that the transition from dendrite to cellular was occurred at the spindle of tip radius and temperature, that was the tip radius and tip temperature reached minimum, VRmin and VTmin. Moreover, solute trapping became obvious during the transition, which led to decrease of microsegregation.
Superhydrophobic Sn/SnOx (x = 1 and 2) films were facilely fabricated by surface self-passivation of three-dimensional (3D) hierarchical porous dendritic Sn while exposed to the air. The porous dendritic Sn was obtained rapidly by electrodeposition accompanying release of hydrogen bubbles. Influence of electrodeposition parameters on the surface morphology and wettabillity has been investigated in detail, including deposition potentials, deposition times and electrolyte concentrations. The maximum contact angle reached to 165 degrees on the porous dendritic Sn/SnOx film electrodeposited in a solution of 60 mM SnCl2 and 1.5 M H2SO4 under -1.7 V for 20 s. Both the hierarchical micro-nanostructures and the spontaneously formed ultrathin surface passivation layer of Sn oxides endow the prepared Sn/SnOx surface with excellent inherent superhydrophobicity without further surface modification.
The new ternary composite composed of RGO, Cu2O and Cu quantum dot was successfully synthesized at room temperature by using NaBH4 as reducing agent under mild wet-chemical conditions. The morphology, structure and microwave electromagnetic properties of the composite were characterized by XRD, XPS, TEM and vector network analyzer. The composite shows a large RL (−51.8 dB at 14.6 GHz) and a wide absorption band (less than −10 dB from 12.1 to 16.2 GHz) with the thickness of only 1.3 mm. The enhanced microwave absorbing properties were also explained, and the loss mechanism is dielectric loss. The ternary composite can act as efficient and lightweight microwave absorbing material.
Superhydrophobic metallic surfaces are attracting wide interest. In this
work, two facile one-step methods (displacement reaction and
electrodeposition) were developed to fabricate superhydrophobic
Bi/Bi2O3 surfaces with hierarchical porous
dendritic structures, where the Bi2O3 cover layer
was formed by surface self-passivation of the deposited Bi. The
influence of various experimental parameters on the surface morphology
and wettability were investigated in detail, including concentration of
solutions, deposition times, and deposition potentials. A maximum
contact angle about 164° can be obtained on the fabricated
superhydrophobic Bi/Bi2O3 surfaces by these two
methods under optimized conditions without additional surface
modification.
A method for controlling the shapes and sizes of Cu nanoparticles during electrodeposition has been developed by tailoring the surface morphologies of TiN-coated electrodes. Larger octahedral Cu NPs grew on a granular TiN film; smaller, irregular Cu NPs formed on a pyramidal TiN film. The surface morphology of the TiN film affected the accumulation of Cu(2+) and hexadecyltrimethylammonium cations (CTA(+)) ions, leading to the different shapes and sizes of the resulting Cu NPs. The significant steric effect of the CTA(+) ions was confirmed when using the film of pyramidal TiN as the electrode in the CTAB-containing electrolyte; it contributed to the growth of the smaller, irregular Cu NPs. The sensitivity of the smaller, irregular Cu NPs in the detection of glucose was better than that of the larger, octahedral Cu NPs because of the former's greater increase in the Cu(2+)-to-Cu(0) ratio.
Self-cleaning surface is potentially a very useful addition for many commercial products due to economic, aesthetic, and environmental reasons. Super-hydrophobic self-cleaning, also called Lotus effect, utilizes right combination of surface chemistry and roughness to force water droplets to form high contact angle on a surface, easily roll off a surface and pick up dirt particles on its way. Electrospinning is a promising technique for creation of superhydrophobic self-cleaning surfaces owing to a wide set of parameters that allow effectively controlling roughness of resulted webs. This article gives a brief introduction to the theory of super-hydrophobic self-cleaning and basic principles of the electrospinning process and reviews the scientific literature where electrospinning was used to create superhydrophobic surfaces. The article reviewed are categorized into several groups and their results are compared in terms of superhydrophobic properties. Several issues with current state of the art and highlights of important areas for future research are discussed in the conclusion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Polystyrene (PS) based superhydrophobic films were prepared by
non-solvent induced phase separation method using tetrahydrofuran (THF)
as the solvent and different alcohols as non-solvents. Flory Huggins
interaction parameter values of different alcohols and acetone with PS
were calculated to qualify them as non-solvents for phase separation.
The films were characterized using contact angle analyser, field
emission scanning electron microscope, surface roughness profilometer,
IR spectrometer and Raman spectrometer. The coatings exhibited a maximum
water contact angle (WCA) of 159° and a sliding angle (SA) <
2°. With increase in the vol% of non-solvent, WCA increased and SA
decreased. The microstructures of the films varied with the vol% of
non-solvent and the amount of PS. The work of adhesion of PS films
decreased with increasing WCA. The Raman spectral studies showed
isotactic to atactic transformation of PS with the addition of
non-solvents and these results corroborated well with the IR spectral
studies.
High mechanical strength superhydrophobic Ni-Cu-P alloy coatings with strong adhesion force were one-step galvanostatically electrodeposited onto low alloy steel substrates, from a citrate- and sulphate-based bath. Surface morphologies of as-deposited Ni-Cu-P coatings were investigated by Scanning Electron Microscope (SEM). The chemical composition, structure, mechanical properties and adhesive/hydrophobic properties of coatings were characterized by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nano-indenter, and contact angle meter, respectively. Results showed that Ni-Cu-P coatings had cauliflower-like micro-nano structures and exhibited stable hydrophobicity under different pH values and high adhesive properties without any chemical modification. Hardness test results showed that hydrophobic Ni-Cu-P alloy coatings exhibited a high hardness of about 8.5 GPa. The deposition process of coatings was proposed to illustrate the formation of cauliflower-like micro-nano structures. The mechanism of the hydrophobic and high adhesion characteristic of this surface was explained by Cassie impregnating model. This method of fabricating hydrophobic surface has potential in practical applications such as micro-droplet transportation, corrosion protection and nano patterning.
Au@Pt core–shell nanoparticles were successfully synthesized by successive reduction of HAuCl4 and H2PtCl6 and were then assembled on Vulcan XC-72 carbon surface (noted as Au@Pt/C). The morphology and distribution of Au@Pt nanoparticles were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) and the corresponding result is that core–shell like structure is observed. The Au@Pt/C catalysts with different Au/Pt atomic ratios were characterized by TEM, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activities of Au@Pt/C catalysts were investigated by cyclic voltammetry (CV) in 1.0 M H2SO4 + 1.0 M methanol aqueous solution. The effects of Au/Pt atomic ratio, CV scan rate and methanol concentration on the peak current of methanol oxidation and the long-term cycle stability were also discussed. The results revealed that compared with Au@Pt/C (1:4, 1:1, 2:1) catalysts, Au/C catalyst, and Pt/C catalyst, Au@Pt/C (1:2) catalyst exhibits higher electrocatalytic activity toward methanol oxidation in acidic media, and the peak current density of Au@Pt/C (1:2) catalyst is about 2.5 times as large as that of Pt/C catalyst without Au core. Further more, Au@Pt/C (1:2) catalyst shows good long-term cycle stability and 91.1% value of peak current of methanol oxidation remains after 200 cycles.
Surfaces with controlled underwater oil wettability would offer great promise in the design and fabrication of novel materials for advanced applications. Herein, we propose a new approach based on self-assembly of mixed thiols (containing both HS(CH2)9CH3 and HS(CH2)11OH) on nanostructured copper substrates for the fabrication of surfaces with controlled underwater oil wettability. By simply changing the concentration of HS(CH2)11OH in the solution, surfaces with controlled oil wettability from the underwater superoleophilicity to superoleophobicity can be achieved. The tunable effect can be due to the synergistic effect of the surface chemistry variation and the nanostructures on the surfaces. Noticeably, the amplified effect of the nanostructures can provide better control of the underwater oil wettability between the two extremes: superoleophilicity and superoleophobicity. Moreover, we also extended the strategy to the copper mesh substrates and realized the selective oil/water separation on the as-prepared copper mesh films. This report offers a flexible approach of fabricating surfaces with controlled oil wettability, which can be further applied to other ordinary materials, and open up new perspectives in manipulation of the surface oil wettability in water.
The work presents a template-free electrochemical route to producing superhydrophobic copper coatings with the water contact angle of 160º ± 6° and contact angle hysteresis of 5° ± 2°. In this technique, copper deposit with multiscale surface features is formed through a two-step electrodeposition process in a concentrated copper sulfate bath. In the first step, applying a high overpotential results in the formation of structures with dense-branching morphology, which are loosely attached to the surface. In the second step, an additional thin layer of the deposit is formed by applying a low overpotential for a short time, which is used to reinforce the loosely attached branches on the surface. The work also presents a theoretical analysis of the effects of the fabrication parameters on the surface textures that cause the superhydrophobic characteristic of the deposit.
Facile preparation of superhydrophobic surfaces of stable and cheap metals is practically important. We report here our findings on fabrication of a superhydrophobic metal Sn surface, which can be obtained at room temperature in 5 min through a displacement reaction between a zinc plate and an acidic SnCl2 solution without needing post-treatment and surface modification. This procedure is facile, time-saving and inexpensive, which is superior to other known displacement depositions of Pt, Ag, Au, or Cu. The effects of preparation conditions on the surface morphology and wettability have been investigated in detail, including reactant concentration and reaction time. It has been observed that superhydrophobicity was closely related with the morphological transition from tin nanoparticles/nanopores to tin dendrites, and the maximal water contact angle (CA) was about 156° with the Cassie state. We expect that this fabrication technique will find practical applications.
In this work, we present a novel facile electrodeposition approach to create micro/nano structure on an anodic copper plate with an alkali ethanol electrolyte solution. The electrolyte solution is composed of potassium hydroxide, potassium persulfate and ethanol. Hierarchical structures were formed on an anodic copper surface by an alkali assistant oxidation process, water immersion and fluorination, the as-prepared surface exhibits superhydrophobic property. The creation of morphological structures and chemical compositions on the treated surface was revealed by scanning electron microscopy (SEM) and X-ray diffraction techniques. The resulting surfaces composing of Cu(OH)2 arrays demonstrates that water contact angle is as high as 165° and the rolling angle is less than 3°. The study is expected to create a new avenue for the basic research as well as real application.
In this work, a superhydrophobic nickel surface is fabricated by coupling electro and electroless deposition without chemical modification. SEM study reveals that electrodeposited nickel surface is characterized by nanocone arrays and has a contact angle of about 135°. After adding electroless deposition, as the second step, hemispherically topped nickel nanocone arrays are formed which leads to a high contact angle of 153.6°. That is, nickel surface has successfully transformed from hydrophobic to superhydrophobic. This transition is investigated both from the aspects of chemical composition and surface structure and proves the latter is the dominant factor. The present study inspires us to do more research about the creation of rough surfaces and enriches our comprehension about superhydrophobicity.
A low-cost and large-scale fabrication method to an environmentally-friendly superhydrophobic coating on magnesium alloy is reported in this paper. The rough surface structure could be facilely obtained by electrodeposition of copper. Then the rough surface could be changed from hydrophilic to superhydrophobic via modification with lauric acid. The as-prepared coatings were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), X-ray diffractometry (XRD), electrochemical corrosion test and electrochemical impedance spectroscopy (EIS). The as-prepared superhydrophobic coatings have ultra-low slide angles (2°) and contact angles of 154°. Our method is of great value for the industrial fabrication of superhydrophobic coatings. It has an excellent anti-corrosion effect and self-cleaning effect.
Dendritic copper film with convertible extreme wettability is prepared on metal surface via electrodeposition. With field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and electrochemical measurement, the morphology, composition and formation mechanism of dendritic copper film were studied. It is found that the film is mainly composed of metallic copper. Also some residual cuprous oxide and chloride exist in the deposit. The single micron-sized dendrite consists of a main stem with side branches, on which the higher-order branches with the dimension of tens of nanometers grow. A hydrophobic modification can induce the conversion of the apparent wettability of film from super-hydrophilicity (with apparent water contact angle of 5±3°) to super-hydrophobicity (with apparent water contact angle of 154.1±3°), which is due to the capillary effect. The method proposed in this paper is time-saving and facile to operate, and it offers a promising technique to prepare metallic surface with a high wettability contrast for water.
In this work, a rapid one-step process is developed to fabricate superhydrophobic cathodic surface by electrodepositing copper plate in an electrolyte solution containing manganese chloride (MnCl2·4H2O), myristic acid (CH3(CH2)12COOH) and ethanol. The superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The shortest electrolysis time for fabricating a superhydrophobic surface is about 1min, the measured maximum contact angle is 163° and rolling angle is less than 3°. Furthermore, this method can be easily extended to other conductive materials. The approach is time-saving and cheap, and it is supposed to have a promising future in industrial fields.
This study investigates the fabrication of a stable superhydrophobic surface with low contact angle (CA) hysteresis using ZnO thin films prepared by cathodic electrodeposition and subsequent gaseous oxidation. The deposition time is a crucial factor in nanostructuring and producing surface roughness of the films. Cathodic electrodeposition for 60 s created a number of nanopillars, which exhibited the highest CA value, i.e., 167.9°. The rough ZnO surface displayed not only enhanced water repellency with low CA hysteresis but also excellent superhydrophobic stability. The application of the Cassie–Baxter model demonstrated that the ZnO nanostructure contributed to increasing the area of a water droplet in contact with air, leading to superhydrophobicity. Such a unique textured surface showed a great potential for the engineering of strong superhydrophobic coatings.
A new strategy was developed to prepare raspberry-like particles by introducing poly(acrylic acid) (PAA)-functionalized polystyrene (PS) particles into hydrolysis reaction of tetraethoxysilane (TEOS). The monodisperse PAA-functionalized PS particles were used as cores and nanosized silica particles were then assembled on the surface of PS particles to construct raspberry-like particles during the hydrolysis process. With the increase of PAA content from 11% to 20% (wt) at the surface of latexes, the diameter of the silica particles assembled at the surface of cores decreased from 124 nm to 36 nm. The structure, morphology and constitution of the PAA-functionalized PS particles and the raspberry-like particles were characterized by Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In addition, the particulate films were constructed by assembling these raspberry-like particles on glass substrates. After surface modification with dodecyltrichlorosilane, superhydrophobic surfaces can be obtained and the contact angle of water on the dual-sized structured surface can be adjusted by the scale ratio of the micro/nano surface structure of raspberry-like particles.
Nanostructured Ni films with high hardness, high hydrophobicity and low coefficient of friction (COF) were fabricated. The surface texture of lotus leaf was replicated using a cellulose acetate film, on which a nanocrystalline (NC) Ni coating with a grain size of 30±4nm was electrodeposited to obtain a self-sustaining film with a hardness of 4.42GPa. The surface texture of the NC Ni obtained in this way featured a high density (4×103mm−2) of conical protuberances with an average height of 10.0±2.0μm and a tip radius of 2.5±0.5μm. This structure increased the water repellency and reduced the COF, compared to smooth NC Ni surfaces. The application of a short-duration (120s) electrodeposition process that deposited “Ni crowns” with a larger radius of 6.0±0.5μm on the protuberances, followed by a perfluoropolyether (PFPE) solution treatment succeeded in producing a surface texture consisting of nanotextured protuberances that resulted in a very high water contact angle of 156°, comparable to that of the superhydrophobic lotus leaf. Additionally, the microscale protuberances eliminated the initial high COF peaks observed when smooth NC Ni films were tested, and the PFPE treatment resulted in a 60% reduction in the steady-state COFs.
After hydrothermally treated in H2O (for Mg alloy and Al alloy) or H2O2 (for Ti alloy), micro-structured oxide or hydroxide layers were formed on light alloy substrates, which further served as the active layers to boost the self assembling of 1H, 1H, 2H, 2H - perfluorooctyltriethoxysilane (PFOTES) and finally endowed the substrates with unique wettability, i.e., superhydrophobicity. For convenience, the so-fabricated superhyrdophobic surfaces (SHS) were abridged as HT-SHS. For comparison, SHS coded as CE-SHS were also prepared based on chemical etching in acid and succedent surface passivation with PFOTES. To reveal the corrosion protection of these SHS, potentiodynamic polarization measurements in NaCl solution (3.5 wt. %) were performed. Moreover, to reflect the long-term stability of these SHS, SHS samples were immersed into NaCl solution and the surface wettability was monitored. Experimental results indicated that HT-SHS was much more stable and effective in corrosion protection as compared with CE-SHS. The enhancement was most likely due to the hydrothermally generated oxide layer by the following tow aspects: on one hand, oxide layer itself can lower the corrosion due to its barrier effect; on the other hand, stronger interfacial bonding is expected between oxide layer and PFOTES molecules.
This review is an exhaustive representation of the electrochemical processes reported in the literature to produce superhydrophobic surfaces. Due to the intensive demand in the elaboration of superhydrophobic materials using low-cost, reproducible and fast methods, the use of strategies based on electrochemical processes have exponentially grown these last five years. These strategies are separated in two parts: the oxidation processes, such as oxidation of metals in solution, the anodization of metals or the electrodeposition of conducting polymers, and the reduction processed such as the electrodeposition of metals or the galvanic deposition. One of the main advantages of the electrochemical processes is the relative easiness to produce various surface morphologies and a precise control of the structures at a micro- or a nanoscale.
Self-cleaning surfaces have drawn a lot of interest for both fundamental research and practical applications. This review focuses on the recent progress in mechanism, preparation, and application of self-cleaning surfaces. To date, self-cleaning has been demonstrated by the following four conceptual approaches: (a) TiO2-based superhydrophilic self-cleaning, (b) lotus effect self-cleaning (superhydrophobicity with a small sliding angle), (c) gecko setae–inspired self-cleaning, and (d) underwater organisms–inspired antifouling self-cleaning. Although a number of self-cleaning products have been commercialized, the remaining challenges and future outlook of self-cleaning surfaces are also briefly addressed. Through evolution, nature, which has long been a source of inspiration for scientists and engineers, has arrived at what is optimal. We hope this review will stimulate interdisciplinary collaboration among material science, chemistry, biology, physics, nanoscience, engineering, etc., which is essential fo...
We describe the fabrication of roselike microstructures by the direct in situ hydrothermal synthesis method. The as-prepared roselike microstructure film exhibits excellent superhydrophilic properties, absorbing a water droplet of 4 μL in less than 40 ms. Moreover, after a further modification with a self-assembled monolayer of octyltrimethoxysilane, the film changes its wetting properties from superhydrophilicity to superhydrophobicity with a contact angle as high as 154° and a tilt angle lower than 3°.
The lotus-leaf-like superhydrophobic copper was fabricated by a facile two-step method without the chemical modification, on which the water contact angle can reach 158° and the water-sliding angle is less than 10°. Reversible superhydrophobicity to superhydrophilicity transition was observed and controlled by alternation of UV irradiation and dark storage. More interestingly, the superhydrophobic surface exhibits superoleophilicity and all those properties can be well used in reversible switch, separating the water and oil and so on.
Cobalt hierarchical structure having intrinsic superhydrophobic property is prepared via an electrochemical growth approach. The structure exhibits aesthetic flower-like morphology. A quenching strategy is employed to elucidate the plausible crystal growth mechanism. Without further hydrophobic organic molecule modification, the hierarchical structure occupying surface exhibits superhydrophobic effect, which is a new superhydrophobicity example achieved from the hydrophilic material. An approach based on computer graphics is utilized to simulate the contact pattern on this non-Euclidean hierarchical structure.Graphical abstractResearch highlights▶ Flower-like cobalt crystal is prepared by electrochemical method without surfactant and template. ▶ Crystal growth mechanism is elucidated in detail. ▶ Without any surface modification to the surface, the structure exhibits intrinsic superhydrophobicity property. ▶ The superhydrophobicity is simulated with computer graphics technique.
A facile method for preparing a superhydrophobic surface was developed by layer-by-layer (LbL) deposition of poly(diallyldimethylammonium chloride) (PDDA)/sodium silicate multilayer films on a silica-sphere-coated substrate followed with a fluorination treatment. First, a silica-sphere-coated substrate that contains loosely stacked silica spheres of 600 and 220 nm was prepared and cross-linked with SiCl 4 . PDDA was then alternately assembled with sodium silicate on the silica-sphere-coated surface to prepare a micro-and nanostructured hierarchical surface. Scanning electron microscopy (SEM) images verify that the deposition of a 5-bilayer PDDA/sodium silicate multilayer film leads to the formation of a micro-and nanostructured hierarchical surface. After chemical vapor deposition of a layer of fluoroalkylsilane, a superhydrophobic surface with a water contact angle of 157.1° and sliding angle of 3.1° was successfully fabricated. The easy availability of the materials and simplicity of this method might make the superhydrophobic surface potentially useful in a variety of applications.
A simple method of electrochemical deposition was adopted to prepare conductive hydrophobic zinc oxide (ZnO) thin films. The surface structures were characterized by sanning electron microscopy (SEM) and atomic force microscopy (AFM). Wettability studies revealed that the surface of the as-prepared thin films showed a contact angle (CA) for water of 128.3 (1.7°, whereas the superhydrophobic surface with a water contact angle of 152.0 (2.0° was obtained by (fluoroalkyl)silane modification. The superhydrophobic conductive thin films materials may have potential use such as microfluidic devices in the future. It is likely that other oxide materials may be similarly prepared by this method.
A new process for preparing transparent superhydrophobic films using a sublimable pore-forming material to provide controllable surface roughness was demonstrated using aluminum acetylacetonate as the model sublimate compound and boehmite and silica as film materials. As evidenced by SEM, XRD and UV-vis-near-IR scanning spectrometry, the process successfully imparted surface roughness to the films during calcination, and formed transparent superhydrophobic films with subsequent coating with fluoroalkylsilane.
A hierarchically micro/nanostructured alumina gel film was prepared by using a simple sol-gel process; upon self-assembly of fluoroalkyl phosphonic acid, a "non-sticky" superhydrophobic surface was obtained.
A stable titanate nanobelt (TNB) particle suspension was prepared by a hydrogen-bond-driven assembly of pre-hydrolysed fluoroalkylsilane (FAS) on its surface. A one-step electrophoretic deposition was applied to fabricate a transparent cross-aligned superhydrophobic TNB/FAS film on a conducting glass substrate. By controlling the deposition time, we have shown the transition between a "sticky" hydrophobic state (high contact angle with strong adhesion) and a "sliding" superhydrophobic state (high contact angle with weak adhesion). The optical transmittance can reach as high as 80% throughout most of the visible light region of the spectrum. These coatings have also displayed high chemical stability and self-cleaning ability. Upon heating the hydrophobic coatings at 500 degrees C, the TNB coating transforms into a porous TiO2(B) structure with superhydrophilic behavior and could be used for anti-fogging applications. With this TiO2-based system, we have demonstrated three different wetting states: superhydrophobicity with weak adhesion, high hydrophobicity with strong adhesion, and superhydrophilicity with immediate water spreading. Moreover, this work has also demonstrated superhydrophobic TNB/FAS films with high chemical stability and good self-cleaning performance and superhydrophilic pore-like TiO2(B) films with rapid water spreading and excellent anti-fogging ability.
Super-hydrophobic surfaces, with a water contact angle (CA) greater than 150°, have attracted much interest for both fundamental research and practical applications. Recent studies on lotus and rice leaves reveal that a super-hydrophobic surface with both a large CA and small sliding angle () needs the cooperation of micro- and nanostructures, and the arrangement of the microstructures on this surface can influence the way a water droplet tends to move. These results from the natural world provide a guide for constructing artificial super-hydrophobic surfaces and designing surfaces with controllable wettability. Accordingly, super-hydrophobic surfaces of polymer nanofibers and differently patterned aligned carbon nanotube (ACNT) films have been fabricated.
Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings. Our recent discovery on the superhydrophobicity of boron nitride nanotubes (BNNTs) is thus contradicting with the fact that BN materials would not be hydrophobic. To resolve this contradiction, we have investigated BNNT coatings by time-dependent contact angle measurement, thermogravimetry, IR spectroscopy, and electron microscopy. We found that the wettability of BNNTs is determined by the packing density, orientation, length of nanotubes, and the environmental condition. The origins of superhydrophobicity of these BNNT coatings are identified as (1) surface morphology and (2) hydrocarbon adsorbates on BNNTs. Hydrocarbon molecules adsorb spontaneously on the curved surfaces of nanotubes more intensively than on flat surfaces of BN films. This means the surface energy of BNNTs was enhanced by their large curvatures and thus increased the affinity of BNNTs to adsorb airborne molecules, which in turn would reduce the surface energy of BNNTs and make them hydrophobic. Our study revealed that both high-temperature and UV-ozone treatments can remove these adsorbates and lead to restitution of hydrophilic BN surface. However, nanotubes have a unique capability in building a hydrophobic layer of adsorbates after a few hours of exposure to ambient air.
A typical superhydrophobic (ultrahydrophobic) surface can repel water droplets from wetting itself, and the contact angle of a water droplet resting on a superhydrophobic surface is greater than 150°, which means extremely low wettability is achievable on superhydrophobic surfaces. Many superhydrophobic surfaces (both manmade and natural) normally exhibit micro- or nanosized roughness as well as hierarchical structure, which somehow can influence the surface's water repellence. As the research into superhydrophobic surfaces goes deeper and wider, it is becoming more important to both academic fields and industrial applications. In this work, the most recent progress in preparing manmade superhydrophobic surfaces through a variety of methodologies, particularly within the past several years, and the fundamental theories of wetting phenomena related to superhydrophobic surfaces are reviewed. We also discuss the perspective of natural superhydrophobic surfaces utilized as mimicking models. The discussion focuses on how the superhydrophobic property is promoted on solid surfaces and emphasizes the effect of surface roughness and structure in particular. This review aims to enable researchers to perceive the inner principles of wetting phenomena and employ suitable methods for creation and modification of superhydrophobic surfaces.
AuPt alloy films with three-dimensional (3D) hierarchical pores consisting of interconnected dendrite walls were successfully fabricated by a strategy of cathodic codeposition utilizing the hydrogen bubble dynamic template. The foam films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Due to the special porous structure, the electronic property, and the assembly effect, the AuPt alloy foam films show superior electrocatalytic activity toward the electrooxidation of formic acid in acidic solution, and the prepared 3D porous AuPt alloy films also show high activity and long stability for the electrocatalytic oxidation of methanol, where synergistic effect plays an important role in addition to the electronic effect and assembly effect. These findings provide more insights into the AuPt bimetallic nanomaterials for electrocatalytic applications.
Superhydrophobic surfaces were prepared on Ti/Si substrates via the fabrication of a platinum (Pt) nanowire array. The Pt nanowire array was obtained by dc electrodeposition of Pt into the pores of an anodic aluminium oxide (AAO) template on the substrate followed by the removal of the template. Transmission electron microscopy (TEM) examination demonstrated that all the nanowires have uniform diameter of about 30 nm. Field emission scanning electron microscopy (FE-SEM) showed that the structures at both the micrometre scale and nanometre scale bestowed the prerequisite roughness on the surfaces. The chemical surface modification made the Pt nanowire array superhydrophobic. The surface modified Pt nanowire array exhibited superhydrophobicity even in corrosive solutions over a wide pH range, such as acidic or basic solutions. The results demonstrated that the Pt nanowire array will have good potential applications in the preparation of superhydrophobic surfaces.
In this review we focus on recent developments in applications of bio-inspired special wettable surfaces. We highlight surface materials that in recent years have shown to be the most promising in their respective fields for use in future applications. The selected topics are divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability and integrated multifunctional surfaces and devices. We will present how the bio-inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.
We demonstrate a mass-production-amenable technology for fabrication, surface modification and multifunction integration in polymeric microfluidic devices, namely direct lithography on the polymeric substrate followed by polymer plasma etching, and selective plasma deposition. We apply the plasma processing technology to fabricate polymeric microfluidics in poly(methyl methacrylate) (PMMA) and poly(ether ether ketone) (PEEK). First, deep anisotropic O(2) plasma etching is utilized to pattern the polymer via an in situ, highly etch-resistant, thin, Si-containing photoresist, or via a thick organic photoresist. Absolute control of surface roughness (from smooth to very rough), and the production of stable-in-time (slowly ageing) superhydrophilic microchannels are demonstrated. Second, we demonstrate the spontaneous capillary pumping through such rough, superhydrophilic plasma-etched microchannels in contrast to smooth ones, even 5 weeks after fabrication. Third, by using C(4)F(8) fluorocarbon plasma deposition through a stencil mask, we produce superhydrophobic patches inside the microchannels, and use them as passive valves. Our approach proposes "smart" multifunctional microfluidics fabricated by a plasma technology toolbox.