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Surface Treatment of Polydimethylsiloxane (PDMS) with Atmospheric Pressure Rotating Plasma Jet. Modeling and Optimization of the Surface Treatment Conditions
Abstract
Surface treatment of polydimethylsiloxane (PDMS) with a rotative nozzle atmospheric pressure plasma jet (APPJ) was reported. Operating conditions were optimized by statistical design of experiments, using water contact angle and XPS as response variables; OES (optical emission spectroscopy) was used for plasma diagnosis. The nozzle-PDMS distance and the torch speed were the most influencing parameters and were optimum at 6.6 mm and 10.3 m s-1, respectively. The extent of hydrophobic recovery of treated PDMS, investigated by water contact angle measurements, was less than what reported in the literature for this amorphous polymer. However, the APPJ treatment proposed in this paper is meant to be inserted in line for a homogeneous surface treatment of PDMS for enhanced adhesion improvement to coatings or adhesives. Nozzle-sample distance and torch speed are revealed as the most influencing factors of atmospheric pressure plasma jet (APPJ) for surface treatment and hydrophilicity enhancement of polydimethylsiloxane (PDMS). Degree of surface modification is correlated with homogeneity of APPJ treatment, plasma composition and temperature, and treatment conditions are optimized through maximizing oxygen content of plasma-treated surface.
... Displacement speeds up to some tens of meters per minute were reported [95,97,101,184,185]. Different studies showed the influence of the scan parameters (e.g., the displacement speed, the distance between two consecutive tracks) on the extent of the surface modification. ...
... Different studies showed the influence of the scan parameters (e.g., the displacement speed, the distance between two consecutive tracks) on the extent of the surface modification. For instance, regarding the plasma treatment of polymeric surfaces for wettability improvement, it was shown that, as expected, the decrease of the scan speed (i.e., the increase of the treatment time) results in a decrease of the WCA of the treated surfaces [184]. In the case of deposition processes, the coating thickness generally decreases with increasing the scan speed [185]; interestingly, thin films characterized by superior retention of the precursor structure can be obtained at high scan speeds, due to the reduced interaction of the plasma with the growing layer [96]. ...
... Although wettability and adhesion enhancement represents a wellestablished application of plasma jets, the research in this field is still active nowadays, as demonstrated by the presence of many recent fundamental and applicative publications on the treatment of both synthetic polymers [38,65,101,107,112,113,184,[242][243][244][245][246][247][248][249][250][251][252], natural organic materials (e.g., cellulosic materials such as paper and cotton) [253,254] and inorganic materials (e.g., metals) [255][256][257]. ...
Atmospheric pressure non-equilibrium (cold) plasma jet technology received enormous attention in surface processing of materials in the last two decades, and still continues nowadays to attract growing interest. In addition to the advantages of the atmospheric pressure operation such as the potential cost reduction of apparatuses as well as their easier handling and maintenance, due to the distinctive remote operation, plasma jets give the unique possibility of placing the substrate outside the source boundaries. Consequently, the processing of complex three-dimensional objects and the integration into existing production lines are expected to be much easier. However, while appealing, plasma jet technology has the drawback that great efforts are required for process optimization, since many factors can affect, for instance, the physical and chemical proprieties of the so-called “plasma plume” emanating from the devices and propagating in open space towards the substrate to be treated. The aim of this paper is to provide a critical literature review on the utilization of atmospheric pressure non-equilibrium plasma jets in surface processing of materials. Starting from the description and classification of the multitude of devices used in this applicative field so far, the attention will be drawn on some very important aspects to be taken into account in process optimization. The discussion will be focused on basic concepts and peculiarities closely related to the remote operation of the plasma sources, which include the characteristics and dynamics of the plasma plume interacting with the substrate and the surrounding atmosphere. Since the plasma jet approach allows the surface modification of small localized regions of the sample, the strategies implemented to enlarge the treated area will be also addressed. Finally, a brief overview will be given of the available applications and recent developments in the field of etching, thin film deposition and treatment.
... It has been shown [33] that the effectiveness of atmospheric pressure plasmas in regards to the improve the adhesive properties of hydrophobic polymers is much faster than by using low-pressure plasmas or corona discharges. The surface treatment of PDMS with corona discharges [34][35][36] and low-pressure plasmas [37][38][39][40][41][42][43][44] has been extensively studied in recent years; however, there are very few studies on the surface treatment of PDMS with atmospheric pressure plasmas and, more specifically, with atmospheric pressure plasma jets [43,44]. ...
... It has been shown [33] that the effectiveness of atmospheric pressure plasmas in regards to the improve the adhesive properties of hydrophobic polymers is much faster than by using low-pressure plasmas or corona discharges. The surface treatment of PDMS with corona discharges [34][35][36] and low-pressure plasmas [37][38][39][40][41][42][43][44] has been extensively studied in recent years; however, there are very few studies on the surface treatment of PDMS with atmospheric pressure plasmas and, more specifically, with atmospheric pressure plasma jets [43,44]. ...
... It has been widely established that the surface modifications of PDMS produced by plasma treatment were lost because of the relatively fast reorientation of the modified polymeric chains grafted to the outermost external surface into the bulk and the migration of the non-polar low-molecular weight polysiloxane species from the bulk to the surface as well [4,22,37,40,[51][52][53][54]. The rate of hydrophobic recovery depends both on the plasma treatment conditions [36][37][38][39][44][45][46][47] and on the storage media during the recovery process [49][50][51][52]; partial or complete hydrophobic recovery is produced within 24 h after treatment, noticeably reducing the hydrophilicity of the PDMS surface properties achieved by plasma treatment. ...
The surface properties of polydimethylsiloxane (PDMS) were modified by treatment with an atmospheric pressure rotating plasma jet (APPJ) and the surface modifications were studied to assess its hydrophilicity and adhesion to acrylic adhesive tape intended for medical applications. Furthermore, the extent of hydrophobic recovery under different storage conditions was studied. The surface treatment of PDMS with the APPJ under optimal conditions noticeably increased the oxygen content and most of the surface silicon species were fully oxidized. A brittle silica-like layer on the outermost surface was created showing changes in topography due to the formation of grooves and cracks. A huge improvement in T-peel and the shear adhesive strength of the APPJ-treated PDMS surface/acrylic tape joints was obtained. On the other hand, the hydrophilicity of the PDMS surface increased noticeably after the APPJ treatment, but 24 h after treatment almost 80% hydrophobicity was recovered and the adhesive strength was markedly reduced with time after the APPJ treatment. However, the application of an acrylic adhesive layer on the just-APPJ-treated PDMS surface retained the adhesive strength, limiting the extent of hydrophobic recovery.
... The control of plasma parameters is critical to achieving effective and consistent plasma modification of materials. The parameters that can be controlled include the gas flow rate, pressure, power, exposure time, and the composition of the gas used for plasma generation [29,30]. The gas flow rate is an important parameter that affects the rate of gas consumption and the gas mixing within the plasma. ...
... Lower pressure can lead to higher plasma densities and longer exposure times, resulting in more significant surface modification. Higher pressure can lead to a more uniform plasma across the substrate and can be beneficial for larger substrates [30]. The power supplied to the plasma is another critical parameter that determines the plasma density and energy. ...
Natural polymers have attracted significant attention in drug delivery applications due to their biocompatibility, biodegradability, and versatility. However, their surface properties often limit their use as drug delivery vehicles, as they may exhibit poor wettability, weak adhesion, and inadequate drug loading and release. Plasma treatment is a promising surface modification technique that can overcome these limitations by introducing various functional groups onto the natural polymer surface, thus enhancing its physicochemical and biological properties. This review provides a critical overview of recent advances in the plasma modification of natural polymer-based drug delivery systems, with a focus on controllable plasma treatment techniques. The review covers the fundamental principles of plasma generation, process control, and characterization of plasma-treated natural polymer surfaces. It discusses the various applications of plasma-modified natural polymer-based drug delivery systems, including improved biocompatibility, controlled drug release, and targeted drug delivery. The challenges and emerging trends in the field of plasma modification of natural polymer-based drug delivery systems are also highlighted. The review concludes with a discussion of the potential of controllable plasma treatment as a versatile and effective tool for the surface functionalization of natural polymer-based drug delivery systems.
... In addition, the CAP treatment of the glass substrate improves the Ag NPs deposition rate, increases the thin film adhesion as well as the density and compactness of the deposited Ag NPs; leading to the fabrication of pinhole-free thin films (Lisco et al. 2017); resulting in the bacterial detection based on protein adsorption (Wigginton et al. 2010). CAP treatment is an environmentally benign technology, considered as a surface modification technique for such materials as polymers (Reche et al. 2016), or inorganic materials (e.g. metals) (Kawase et al. 2014;Hosseinpour et al. 2019). ...
... Different authors have stated that the increase in surface hydrophilicity upon plasma treatment is only temporary (e.g. Reche et al. 2016). For our experiment, where the purpose is to enhance the wettability of the silver thin film surface, it is necessary to study the hydrophobic recovery or ageing process. ...
In this study, for the first time, to our knowledge, a biosensor was produced using cold atmospheric plasma (CAP) treatment of silver thin film surface with non-perpendicular incidence angle for identification of Escherichia coli in distilled water. Field emission scanning electron microscopy (FESEM) exhibits that before deposition, non-perpendicular CAP treatment of glass surface substrate leads to the production of pinhole-free silver thin film. The results of atomic force microscopy (AFM) and curve fitting show that non-perpendicular CAP treatment of this pinhole-free silver thin film indicates to the appearance of Ag NPs with smaller size and larger surface area compared to untreated silver film deposited on the untreated glass substrate. The silver-based pinhole-free SPR biosensor produced with non-perpendicular CAP treatment of both glass substrate and silver film shows E. coli detection in the distilled water in the range of 104 colony forming unit (CFU/ml) to 108 CFU/ml with better sensitivity compared to the untreated silver-based SPR biosensor. HIGHLIGHTS
The glass substrate was treated using CAP for improving the silver film adhesion.;
FESEM analysis was performed for observation of pinholes in thin film.;
A silver-based SPR biosensor was fabricated using non-perpendicular CAP treatment for E. coli detection in water.;
The effect of non-perpendicular CAP on the performance parameters of pinhole-free silver biosensor was studied.;
... Several studies have reported the use of such technologies for the preparation of different types of materials such as pure polymers [1][2][3][4], composites [5][6][7][8], and metals [9][10][11][12]. However, most studies have concentrated on the first two types. ...
... In most cases, the optimization of a specific system is studied, focusing on a single substrate and, in some cases, on the effects of treatment on surface modification. For example, Jofre-Reche et al. [2] investigated the atmospheric pressure plasma jet (APPJ) surface treatment of polydimethylsiloxane (PDMS) using the design of experiments (DoE) approach, focusing on the WCA and XPS outcomes as objective functions. Numerical analysis was used to determine the effects of the main process parameters and to optimize the treatment of PDMS. ...
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In this study, the design of experiments (DoE) approach was used to identify the effect of low-pressure plasma surface treatment parameters on the lap-shear strength of adhesive bonded joints realized using different sub-strates. In particular, four different polymeric substrates were considered: 5-and 7-layer carbon-fiber reinforced polymers and polyamide 6 and 6.6. Two-level, full-factorial designs were used to investigate the effects of two varying principal parameters, namely, plasma power and treatment time, for each type of substrate. The analysis was carried out by considering different types of processing gases. The objective function was the tensile shear strength of the adhesively bonded joints. For each set of joints, the shear strength values were compared using the DoE approach to detect any systematic behavior among different substrates. Finally, it was possible to identify the setup parameters that gave the best performance in terms of shear strength, considering any equivalent conditions from a statistical point of view. This aspect is particularly important in consideration of the process optimization of the manufacturing cycle; indeed, it allows the maximization of the joint efficiency by limiting the energy cost for treatment.
... The plasma conditions used were fixed for this study and were the following: Nozzle-distance = 10 mm; f = 21 kHz, speed = 15 m/min; PCT = 80%; number of scans = 2-7. In these conditions the gas temperature at a distance of 10 mm from the Fig. 3 Schematic of the rotating atmospheric pressure jet nozzle was 500 K [33]. However, the temperature drops down very quickly from the nozzle to the surface of the polymer, and because of the rotation of plasma jet at high rate, the surface temperature of UHMWPE measured by infrared camera was between 40 and 50 °C for 2-7 scans respectively. ...
... By deconvoluting the N1s photoelectron peak, besides amine/amide functional groups identified on both DBD and r-APPJ treated polymer, NO 2 /NO 3 moieties were detected on APPJ-treated surface. Indeed, optical emission spectra of the blown arc, air plasma jet is dominated by a broad continuum centered at 630 nm attributed to the chemiluminescence of NO 2 species [33,35], which will then be easily grafted to the surface of the plasma activated UHMWPE. The detection of 0.4% of nitrogen on the surface of UHMWPE in the case of the He + 2% O 2 treatments is because of the efficient excitation of He ions and metastables with nitrogen originating from residual air in the DBD reactor. ...
In this research work we demonstrated that a helium/oxygen Dielectric Barrier Discharge conferred hydrophilic functional groups onto the surface, which lead to enhanced bioactivity of UHMWPE without affecting the biocompatibility of the polymer. The latter was checked by increased adhesion of fibroblast cells to the polymer. The effects of the He/2% O2 DBD plasma was compared for the first time to a rotating blown arc atmospheric pressure plasma jet (r-APPJ) in air. The results show a better functionalization as well as stability of the surface properties of the films treated with the DBD. The surface modified UHMWPE once immersed in a Simulated Body Fluid induced the formation of nucleus of hydroxyapatite (calcium phosphate) leading to the growth of a thick apatite coating which was followed up to 14 days, which can be expected to be highly bioactive. Surface characterization techniques also showed different chemical moieties in the case of the two different atmospheric discharges. DBD discharge in He/2% O2, leading to more stable polar functions grafted to a crosslinked polymer surface, proved to be more bioactive than UHMWPE treated by a r-APPJ in air. The latter treatment lead to grafting of less oxygen containing groups to the surface as well as to LMWOM created on r-APPJ treated UHMWPE which are unstable in aqueous media used both in SBF and fibroblasts in DMEM.
Graphic Abstract
... Common process gases include compressed air, oxygen, nitrogen [3], argon [10] or helium-based gas mixtures [11]. Aside from the process gas and system-related parameters such as the shape of the plasma jet, the jet distance to the substrate and the jet speed have the greatest influence on the process result [7,12]. Moroni et al. investigated the APPJ treatment on PA66 and concluded that lower jet distance and low jet speed lead to best results for adhesive bonding in their setup [13]. ...
To quantify the influence of absorbed water in PA6 on the pre-treatment and bonding process, an unfilled and unreinforced PA6 material is investigated in a dried and saturated state. The material is pre-treated by atmospheric pressure plasma jet (APPJ) with varying jet distances. The surfaces are investigated by contact angle measurements, DSC and FTIR to detect molecular and morphological changes in the surface. To evaluate the bonding strength, samples are bonded with a two-component polyurethane adhesive and a two-component acrylate adhesive and tested in a lap shear and a tensile configuration. The results show that water content has a significant influence on the effectivity of the pre-treatment process and the resulting bonding strength and failure mechanism. The adhesion is majorly affected, however these effects do not influence the macroscopic wetting behavior and cannot be measured in contact angles. FTIR spectra and DSC scans do not show significant changes in molecular groups or crystallinity that would explain the observed adhesion improvement in dried samples. High bonding strength is only achieved with adherents at low water content.
... Massines et al [144] used a scanning stage to move the substrate below an RF jet, and Han et al used a scanned 23 kHz plasma jet to treat large areas [145]. The scanning speed and scan interval can affect the treatment uniformity over large areas [146,147]. Generally, the plasma source is scanned across the substrate in a raster fashion, with overlapping scan tracks. The spacing between each can must be optimized to achieve adequate processing uniformity [148]. ...
Polymer materials are widely employed in many fields due to the ease with which they can be formed into complex shapes, their versatile mechanical properties, light weight, and low cost. However, many applications can be hindered by the chemical compatibility of the polymer surface, which is generally hydrophobic and bonds poorly to other media such as paints, glues, metals and biological samples. While polymer surfaces can be treated by wet chemical processes, the aggressive reagents employed are detrimental to the environment, limiting the range of modifications that can be achieved in an industrial context . Plasma functionalisation is an attractive alternative, offering great versatility in the processed surface characteristics, and often using only environmentally benign rare gases, oxygen and nitrogen, as well as organic precursors. Since the modified surface is only a few monolayers thick, the processes are extremely rapid and low in cost. The first industrial process to be developed was plasma oxidation, increasing the surface energy of the polymer to allow adhesion of paint, glue and metal to the component. This polymer surface functionalisation can be achieved with both low-pressure plasmas and with atmospheric pressure discharges. Subsequently many other processes have emerged, allowing other functional groups to be grafted, including amines, hydroxyl and carboxylic acid groups. Plasma polymerisation, starting from gaseous monomers, allows a whole new family of surface chemistries to be created. These processes have many exciting applications in the biomedical field due to the control they give on biocompatibility and selective interaction with living cells. This article will present the fundamentals of plasma interactions with polymers, the plasma devices employed (both at low-pressure and at atmospheric pressure), their advantages and drawbacks, and a range of current and future applications.
... Jofre-Reche et al. [18] investigated the effect of the nozzle distance to the polydimethylsiloxane (PDMS) sample surface (in the range up to 10 mm) and found an optimum surface wettability at the distance of 6.6 mm. This correlated well with the lower gas temperature at this distance and higher optical emission intensity (OES) of O (777 nm) line in the plasma jet. ...
A useful technique for pre-treatment of polymers for improved biocompatibility is surface activation. A method for achieving optimal wettability at a minimal thermal load and unwanted modifications of the polymer properties is elaborated in this paper. Samples of polyethylene terephthalate polymer were exposed to an atmospheric-pressure plasma jet created by a high-impedance low-frequency discharge in wet argon. Different treatment times and distances from the end of the glowing discharge enabled detailed investigation of the evolution of surface activation. A rather fast saturation of the surface wettability over the area of the order of cm2 was observed upon direct treatment with the glowing discharge. At a distance of few mm from the glowing discharge, the activation was already two orders of magnitude lower. Further increase of the distance resulted in negligible surface effects. In the cases of a rapid activation, very sharp interphase between the activated and unaffected surface was observed and explained by peculiarities of high-impedance discharges sustained in argon with the presence of impurities of water vapor. Results obtained by X-ray photoelectron spectroscopy confirmed that the activation was a consequence of functionalization with oxygen functional groups.
... 大气压下的低温等离子体射流可以在空气环境中 产生等离子体羽, 实现放电区和应用区分离, 且等离子 体羽具有丰富的活性粒子 [1,2] . 因此, 等离子体射流在 表面改性 [3,4] 、水处理 [5,6] 、癌症治疗 [7,8] 等众多领域具 有广泛的应用潜力. ...
... In general terms, polymer materials are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties. On the other hand, hydrophilicity could be beneficial in a huge number of applications involving adhesive bonding, painting, labelling and traceability [3][4][5]. The only way to increase the hydrophilic properties of the surfaces is to carry out a surface treatment. ...
Polyolefins are considered among the most difficult polymeric materials to treat because they have poor adhesive properties and high chemical barrier responses. In this paper, an in-depth study is reported for the low pressure plasma (LPP) treatment of neutral polypropylene to improve adhesion properties. Changes in wettability, chemical species, surface morphology and roughness of the polypropylene surfaces were evaluated by water contact angle measurement, X-ray photoelectron spectroscopy and, furthermore, atomic force microscopy (AFM). Finally, the bonded joints were subjected to tensile tests, in order to evaluate the practical effect of changes in adhesion properties. The results indicate that plasma is an effective treatment for the surface preparation of polypropylene for the creation of bonded joints: contact angles decreased significantly depending on the plasma-parameter setup, surface morphology was also found to vary with plasma power, exposure time and working gas.
... Low-temperature plasma jets at atmospheric pressure can generate remote plasma plumes in open air. Due to abundant active species in them [1,2], plasma jets have application potential in extensive fields, such as surface modification [3,4], water treatment [5,6], and cancer therapy [7,8], etc. ...
Far different from conical plumes, regularly-swelling plumes are generated in an atmospheric pressure argon plasma jet excited by a biased sinusoidal voltage at low frequency. Depending on the polarity of bias voltage, the plumes with periodic swells can be solid or hollow. Results indicate that discharge initiates once per voltage cycle, which appears in the negative and positive half cycles for the solid and hollow plumes, respectively. By fast photography, it is found that streamers are involved propagating downstream of the argon flow for the two plumes. Transversely, the streamer diffuses for the solid plume, while it propagates only in the flow periphery for the hollow plume. Due to a high field, intense discharges near the nozzle provide the following swell positions with active species, which can remarkably enhance the discharges there and induce the swells. This formation mechanism of periodic swells is verified through investigating the distance of two adjacent swells as a function of gas flow rate and driving frequency. Moreover, spatial distributions of excited electron temperature and streamer propagation velocity are qualitatively explained based on the mechanism.
... As an excellent casting material, PDMS can have an accurate replica of mold even in nanoscale [26]. The surface properties of PDMS can be easily modified with various physical (e.g., plasma) [27,28] or chemical surface treatment methods [29,30]. However, there are also some drawbacks of using PDMS in microfluidics, such as absorb of solvent and the collapse of channels after bonding [31]. ...
Microfluidics has been widely used in the biological, chemical and recently in the energy field. In the past decade, microfluidics has experienced tremendous growth in academia; researchers in various fields have been using microfluidics as a powerful tool for the enchantments of their research. However, the fabrication technologies of microfluidics are sourced from microelectromechanical systems and integrated circuit industry, which the fabrication process is costly and time-consuming, with the need of highly sophisticated instruments and experienced technical personnel to conduct fabrication process in the cleanroom environment. To lower the technical Barriers for microfluidics, more and more researchers in different fields have invented various low-cost fabrication methods for microfluidics using polymers or paper materials. Comparing to the conventional microfabrication process conducted in the cleanroom, the low-cost fabrication methods are more flexible, with significant reduction in material cost, fabrication cost and processing time. This review is trying to introduce the most recent developments in low-cost microfluidics, from the aspects of materials, microfabrication and bonding technologies. The comparison and scope of application for different low-cost fabrication technologies for microfluidics were also provided in this review.
... Moreover, a virgin pig skin, which was studied in our previous research [14], was prepared and a cooperation test in this section was conducted as well. All surface roughnesses of these samples are shown in the following figures and Tables 1 and 2. For the hardness tactile discrimination test, five different mass ratios of PDMS and curing agent (Sylgard 184 silicone elastomer kit, Auburn, AL, USA) mixtures were prepared, respectively, as different mass ratios lead to different hardness [44]. The mixtures were vacuumed for 20 min in a vacuum drier at 25 • C and then heated at 80 • C for 40 min in a lab oven. ...
The human fingertip is an exquisitely powerful bio-tactile sensor in perceiving different materials based on various highly-sensitive mechanoreceptors distributed all over the skin. The tactile perception of surface roughness and material hardness can be estimated by skin vibrations generated during a fingertip stroking of a surface instead of being maintained in a static position. Moreover, reciprocating sliding with increasing velocities and pressures are two common behaviors in humans to discriminate different materials, but the question remains as to what the correlation of the sliding velocity and normal load on the tactile perceptions of surface roughness and hardness is for material discrimination. In order to investigate this correlation, a finger-inspired crossed-I beam structure tactile tester has been designed to mimic the anthropic tactile discrimination behaviors. A novel method of characterizing the fast Fourier transform integral (FFT) slope of the vibration acceleration signal generated from fingertip rubbing on surfaces at increasing sliding velocity and normal load, respectively, are defined as kv and kw, and is proposed to discriminate the surface roughness and hardness of different materials. Over eight types of materials were tested, and they proved the capability and advantages of this high tactile-discriminating method. Our study may find applications in investigating humanoid robot perceptual abilities.
... Therefore, details on how the plasma breaks and adds bonds on the poly mer surface are largely unknown, making optimisation of the plasma device an empirical and time-consuming process. Traditionally there have been low pressure treatments [5][6][7][8], but more recently there has been a focus on atmospheric pressure devices such as dielectric barrier discharge [9][10][11][12], coronal discharge [13], atmospheric glow discharge [14], or APPJs [15][16][17][18][19][20]. It is worth noting that all of this work has been done with devices where the plasma is in contact with the polymer surface. ...
Plasma treatments are common for increasing the surface energy of plastics, such as polypropylene (PP), to create improved adhesive properties. Despite the significant differences in plasma sources and plasma properties used, similar effects on the plastic film can be achieved, suggesting a common dominant plasma constituent and underpinning mechanism. However, many details of this process are still unknown. Here we present a study into the mechanisms underpinning surface energy increase of PP using atmospheric-pressure plasmas. For this we use the effluent of an atmospheric-pressure plasma jet (APPJ) since, unlike most plasma sources used for these treatments, there is no direct contact between the plasma and the PP surface; the APPJ provides a neutral, radical-rich environment without charged particles and electric fields impinging on the PP surface. The APPJ is a RF-driven plasma operating in helium gas with small admixtures of O2 (0–1%), where the effluent propagates through open air towards the PP surface. Despite the lack of charged particles and electric fields on the PP surface, measurements of contact angle show a decrease from 93.9° to 70.1° in 1.4 s and to 35° in 120 s, corresponding to a rapid increase in surface energy from 36.4 mN m⁻¹ to 66.5 mN m⁻¹ in the short time of 1.4 s. These treatment effects are very similar to what is found in other devices, highlighting the importance of neutral radicals produced by the plasma. Furthermore, we find an optimum percentage of oxygen of 0.5% within the helium input gas, and a decrease of the treatment effect with distance between the APPJ and the PP surface. These observed effects are linked to two-photon absorption laser-induced fluorescence spectroscopy (TALIF) measurements of atomic oxygen density within the APPJ effluent which show similar trends, implying the importance of this radical in the surface treatment of PP. Analysis of the surface reveals a two stage mechanism for the production of polar bonds on the surface of the polymer: a fast reaction producing carboxylic acid, or a similar ketone, followed by a slower reaction that includes nitrogen from the atmosphere on the surface, producing amides from the ketones.
... This might result from the stronger Ar discharge induced more obvious overpopulation of OH(A 2 Σ + ), and a more detailed study on this issue should be further addressed. [44] reported surface treatment of polydimethylsiloxane (PDMS) with a rotating APPJ, and they found that operating conditions, such as the nozzle-PDMS distance and the torch speed, affected the treatment effect and uniformity. Therefore, there is no doubt that the experimental parameters in this work, such as the feed speed and rotational speed of the PTFE tube and the intertube distance, need to be optimized by statistical design to realize optimum hydrophilization of the tubes, and detailed experiments are in process to explore the relationship between plasma treatment parameters and wettability. ...
Plasma hydrophilization is a general method to increase the surface free energy of materials. However, only a few works about plasma modification focus on the hydrophilization of tube inner and outer walls. In this paper, we realize simultaneous and long-lasting plasma hydrophilization on the inner and outer walls of polytetrafluoroethylene (PTFE) tubes by atmospheric pressure plasmas (APPs). Specifically, an Ar atmospheric pressure plasma jet (APPJ) is used to modify the PTFE tube's outer wall and meanwhile to induce transferred He APP inside the PTFE tube to modify its inner wall surface. The optical emission spectrum (OES) shows that the plasmas contain many chemically active species, which are known as enablers for various applications. Water contact angle (WCA) measurements, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) are used to characterize the plasma hydrophilization. Results demonstrate that the wettability of the tube walls are well improved due to the replacement of the surface fluorine by oxygen and the change of surface roughness. The obtained hydrophilicity decreases slowly during more than 180 d aging, indicating a long-lasting hydrophilization. The results presented here clearly demonstrate the great potential of transferring APPs for surface modification of the tube's inner and outer walls simultaneously.
Polymer materials have played crucial roles in current electrical device/equipment especially in rapidly developed dielectric energy storage field, due to their excellent insulation property, low dielectric loss, lightweight, flexibility and good processability. Typical several strategies including monomer/molecule structure design, aggregation structure regulation and nanocomposite strengthening have acquired numerous processes. However, it is always ignored in existed work that insulation failure of polymer material generally starts from surface, and high-frequency electric field can greatly accelerate this failure process. Here surface modification engineering (SME) on polymer materials with a scalable, rapid and low-cost characteristic presents unique superiority in solving current problems. In this Review, we summarize various SME approaches on polymer materials and discuss introduced variations in surface morphology, physicochemical structure and charge transport behavior. We analyze how particular chemical groups anchoring, organic-inorganic deposition, physicochemical evolution and micro-nano structure design of modification surface can be modulated to obviously enhance multilevel insulation properties (from surface to interior even under high-frequency electric field) and subsequent dielectric energy storage performances. In addition, we highlight the multifunctionality and stability of modification surface on polymer materials, which examines the possibility of synergistically improving other performances like antifouling and anti-corrosion toward complicated/hash insulation scenes and advanced energy storage. Finally, we analyze current challenges in this field and offer a prospect for future development toward high-performance and large-scale practical applications.
Microfluidic devices serve as essential tools across diverse fields like medicine, biotechnology, and chemistry, enabling advancements in analytical techniques, point‐of‐care diagnostics, microfluidic cell cultures, and organ‐on‐chip models. While polymeric microfluidics are favoured for their cost‐effectiveness and ease of fabrication, their inherent hydrophobic properties necessitate surface functionalization, often post‐sealing. Here, we introduce a versatile apparatus for functionalizing sealed microfluidic devices using atmospheric plasma processing, with a focus on PDMS (polydimethylsiloxane) microfluidics. Through meticulous analysis of surface properties and capillary speed, before and after plasma treatment, along with a comparison between vacuum and atmospheric plasma functionalization methods, we demonstrate the efficacy of our approach. Subsequent experimentation within 3D PDMS microfluidic chambers, combining atmospheric pressure plasma treatment with collagen coating to facilitate mesenchymal stem cells (MSCs) growth over five days, reveals enhanced initial cell adhesion and proliferation, highlighting the potential of our method for improving cell‐based applications within microfluidic systems.
Polydimethylsiloxane (PDMS) is widely used for microfluidic and biomedical applications because of its chemical inertness and affordability. However, its low surface energy limits its adhesion properties, thus necessitating mandatory surface activation, via plasma treatments or chemical processing, especially for improving its hydrophilicity. In this study, we employed an atmospheric pressure plasma jet (2 W) in order to enhance the PDMS surface adhesion for application in microfluidic devices. Treatment variables, including exposure and recovery time and adhesion quality, were investigated. It was possible to achieve a minimum exposure time of 15 s/cm2 for thin PDMS (sheet, 250 μm) and 30 s/cm2 for thick (resin, 3 mm) PDMS. A robust and efficient methodology for scaling the jet system treatment of larger areas was developed. Additionally, we examined the effect of ambient humidity on the plasma treatment. Results showed that water adsorption on PDMS-treated surfaces indicated a difference between the well-established contact angle method for determining surface hydrophilicity (and thus, its adhesion) and the real adhesion properties of the treated surfaces.
Plasma treatment of polypropylene (PP) is a well‐established method of improving its surface properties. However, the efficiencies of different plasma discharges are seldom compared. Herein, we discuss the differences in PP treated by three arc‐based commercial plasma jets working in dry air, Plasmatreat rotating plasma jet (PT‐RPJ), AFS PlasmaJet® (AFS‐PJ), and SurfaceTreat gliding arc jet (ST‐GA), and by the low‐temperature RF plasma slit jet (RF‐PSJ) working in argon. The AFS‐PJ has a significantly different reactive species composition dominated by nitrogen oxides. It induced higher thermal loads leading to surface damage. The other arc‐based jets (PT‐RPJ and ST‐GA) created the PP surface with higher oxygen and nitrogen concentration than the low‐temperature RF‐PSJ. It induced a higher adhesion strength measured on PP‐aluminum joints.
Published data on the effect of low-temperature plasma on polydimethylsiloxane have been analyzed.
Changes in the contact properties, chemical structure, and morphology of the modified polymer surface
have been revealed using modern research techniques (contact angle measurement, X-ray photoelectron
spectroscopy, Fourier-transform IR spectroscopy, atomic force and scanning electron microscopy). It has
been shown that modification by plasma results in the formation of a hybrid material that has the surface layer
consisting mainly of silicon oxide. Plasma-enhanced chemical vapor deposition processes of hexamethyldisiloxane
polymerization on various substrates are considered and the formation of similar hybrid materials
containing a significant amount of silicon oxide is shown. Data on the use of such materials in biology, medicine,
membranes, humidity sensors, and other fields of science and technology are presented.
In recent years, improving the surface properties of large-scale insulation by plasma modification has attracted extensive attention with the development of power systems and high-tech industries. However, routine evaluations of the modification effect and uniformity require complicated tests after the plasma is powered off, which waste a lot of time and cannot regulate the modification effect online. In this study, a novel fluorescence-assisted dielectric barrier discharge (DBD) for fabricating a functional film is developed, and a rapid evaluation method of the modification effect and uniformity is proposed based on fluorescence coloring and image processing technologies. The results show that the addition of an organic fluorescent agent in the DBD with hexamethyldisiloxane (HMDSO) has no negative effect on the plasma discharge and modification effect, and the fluorescence-assisted DBD successfully fabricates the functional films with typical chromogenic groups (N-H and S═O) that exhibit typical fluorescence under an UV lamp. According to image processing and parameter extraction, the plasma-assisted fluorescent film is converted into a two-dimensional (2D) color map with nine color levels, and three characteristic parameters are proposed to evaluate the modification effect rapidly and directly. It shows that the warmer the color of the treated sample, the better the hydrophobicity and electrical insulating properties, where the red region represents the optimally modified surface, while the blue region represents the worst one. The area, shape, and integrity of the plasma modification are clarified quantificationally, which provides the possibility of further online evaluation of the modification effect and uniformity by the plasma treatment.
Epoxy resin (EP) is one of the most widely-used insulating support materials in electrical power systems, with its insulating performance playing an important role in high-voltage engineering. In this study, a nanosecond pulse-driven Ar/Octamethylcyclotetrasiloxane (OMCTS) plasma jet is developed for fabricating nanocomposite dielectric materials to enhance their EP properties. It is demonstrated that the plasma-enabled polymerization effectively modifies the physical morphology and chemical composition of EP surfaces, where the surface roughness greatly increases with the deposition of less-polar silicon-containing films. Moreover, with an increased OMCTS carrier gas flow rate, the surface conductivity of the EP increases by two orders of magnitude, which is directly related to the appearance of shallow traps in the dielectric surface after Ar/OMCTS plasma treatment. Results show that the trap depth of the electron decreases from 1.21 to 0.99 eV post-treatment, with the OMCTS fragments becoming shallow trap points for charge detrapping and transportation processes. Moreover, the addition of a controlled amount of OMCTS increases the plasma discharge intensity, promotes silicon film deposition, and thus significantly improves the insulation and wettability performance, with higher flashover voltages and water contact angles (WCA). By contrast, excessive addition of OMCTS inhibits the plasma discharge due to the absorption and consumption of energetic electrons by OMCTS molecules. Quantum chemistry calculations are further developed to explore the mechanisms of plasma-induced surface modifications. Overall, the proposed plasma polymerization strategy offers a promising fabrication technique and provides guiding insights into the fabrication of nanocomposite dielectric materials in electrical engineering.
A plasma jet with inert working gas operates in a streamer discharge mechanism. The propagation behavior of streamers determines the distribution of active species, which play a key role in the applications of plasma jets. To make clear streamer behavior under the influence of residual positive ions, a two-dimensional fluid model based on the continuity, the conservation, and Poisson's equations is employed to numerically investigate the dynamic behavior of a positive streamer when it approaches a cloud of positive ions with different densities and scales. Results indicate that the streamer always propagates along the axis and passes through the cloud of positive ions if the ions are rarefied (1.0 × 10¹⁶ m⁻³ in the core), which behaves like a free streamer. If the ion cloud has a medium density (5.0 × 10¹⁶ m⁻³ in the core), the streamer first deflects upward when it approaches the vicinity of the ion cloud and then deflects downward when it departs from the ion cloud, leaving a detouring track. The detouring track is also left if the ions are fairly dense (1.0 × 10¹⁷ m⁻³ in the core). However, the detouring process is fulfilled by the relay of two streamers, which are initiated at the jet nozzle and inside the ion cloud, respectively. Moreover, the velocity of the streamer is simulated with varying ion densities, voltage amplitudes, and gap widths. In addition, the deflection amplitude of the detouring track is investigated as a function of the voltage amplitude, gap width, ion density, cloud position, and cloud scale.
The authors reviews the main applications of polydimethylsiloxane in
urinary tract devices and the associated complications. As new solutions
are needed to reduce bacterial adhesion and biofilm formation on
polydimethylsiloxane -based devices, a testing platform is described to
evaluate surface performance in both urinary catheters and ureteral stents.
Also examined are the properties which make polydimethylsiloxane an
excellent candidate for understanding complex biological behaviors,
including its transparency for applying optical methods, biocompatibility
and nontoxicity, high conformity with cells and other biostructures, gas
permeability for the transfer of nutrients and oxygen, and flexibility.
In the subsequent study, a hybrid material of titanium dioxide and
polydimethylsiloxane is obtained and characterized using a sol-gel and electrospraying method. These results indicate that the hybrid material may
be viable as an adsorbent, and that the optimization of the process could
reduce both cost and analysis time.
In order to further the applications of polydimethylsiloxane, the
closing study describes the steps in the fabrication of its plasmonic
structure, and also examines the switching effect of the sample.
The uniformity of the microplasma array is essential to modify the hydrophilicity of the inner surface of polydimethylsiloxane (PDMS) microchannels by plasma treatment. In this study, the effects of applied voltage waveforms on the uniformity of the microplasma array are investigated. Interestingly, the microplasma array excited by AC (alternate current) voltage looks more “uniform” by a digital camera and has higher gas temperature and electron density than that excited by unipolar and bipolar pulse voltage. Imaging the microplasma array by a fast intensified charge‐coupled device camera shows that the ignition of microplasma inside each microchannel has strong randomness in spatial distribution, and the opportunity of each microchannel being ignited is almost equal. Detailed analysis reveals that the low density of surface charges and the small overvoltage in the case of AC voltage are expected to play crucial roles in the stochastic behavior of microplasma ignition inside PDMS microchannels. This study is useful for understanding the uniformity of the microplasma array for surface modification of PDMS microchannels. The uniformity of the microplasma array is essential to the hydrophilicity modification of the inner surface of polydimethylsiloxane (PDMS) microchannels by plasma treatment. The effects of applied voltage waveforms on the uniformity of the microplasma array are investigated in this work. Interestingly, the microplasma array excited by ac voltage looks more “uniform” by a digital camera than that excited by unipolar and bipolar pulse voltage.
In this study, the effect of observed pinholes in the Field emission scanning electron microscopy (FESEM) images on the performance of a silver-based surface plasmon resonance (SPR) biosensor is designed and analytically investigated by a finite element method using COMSOL multiphysics. The simulation results show that the sensitivity and figure of merit (FOM) enhancement of biosensor is attributed to the cold atmospheric-pressure plasma (CAP) treatment of glass substrate before deposition; leading to the omission of pinholes. This work is proposing a new way for SPR biosensors development using surface quality control of the deposited thin films with CAP treatment.
Atmospheric-pressure plasma polymerization of organosilicon precursors such as hexamethyldisiloxane is a well-known process used in the development of SixOyCz thin films on various substrates in different plasma configurations. Typically, long treatments or multi-pass treatments are used to achieve a sufficient thickness. However, the effects of multiple deposition passes on surface properties are rarely considered. In this paper, the development of a superhydrophobic organosilicon-based coating on pre-treated micro-roughened Al-6061 substrates through multiple deposition passes with an atmospheric-pressure plasma jet is reported. It is shown that besides the expected effect on coating's thickness, multiple passes of plasma deposition can also alter surface morphology and surface chemistry through a mechanism similar to the activation of organosilicon substrates with oxygen-containing plasmas. While the increase in coating thickness enhances coating stability in aggressive conditions, the rise of oxygen content reduces the hydrophobic behaviour of the coating.
PDMS is one of the most widely used polymers for the fabrication of biomedical devices. Of particular relevance is the application of PDMS in urinary tract devices such as urinary catheters and ureteral stents. As these devices are being used by a growing number of patients and indwelling times are increasing in an aging population, the incidence of urinary tract infections is rising. These infections have implications on the quality of life of the patients and represent a severe burden on healthcare systems.
This chapter reviews the main uses of PDMS in urinary tract devices and associated complications. As new solutions are needed to reduce bacterial adhesion and biofilm formation on PDMS-based devices, a testing platform is described to evaluate surface performance in both urinary catheters and ureteral stents. Examples of these solutions are also discussed in a quest for more efficient urinary tract devices.
The surface modification of poly (ethylene terephthalate) (PET) film was achieved by two sequential atmospheric pressure plasma jet (APPJ) treatments: plasma-induced polymer coating with hexamethyldisiloxane (HMDSO) and plasma oxidation with nitrogen gas. For comparison with APPJ-oxidation, oxidation by excimer ultra violet (UV) light irradiation was performed. The sessile drop and Wilhelmy contact angle measurements revealed that the PET film subjected to APPJ-coating showed superior water repellency and subsequent APPJ- or UV-oxidation made the PET film super-hydrophilic. UV-oxidation was also performed on the PET film treated by APPJ-coating, covered by a metal mesh. The difference in the contact angles between the surface areas covered with and without the metal strip mask was evident based on the Wilhelmy contact angle measurement. Both hydrophobic and hydrophilic surfaces did not exhibit contact angle hysteresis and had excellent stability of wettability. Furthermore, the hydrophilic surface treated only by APPJ- or UV-oxidation exhibited contact angle hysteresis and hydrophobic recovery with prolonged storage. Field emission scanning electron microscopy (FE-SEM) and SEM observation revealed that the morphology of the PET surface became granular after APPJ-coating. From the analyses of X-ray photoelectron spectroscopy (XPS) and grazing-angle attenuated total reflectance Fourier transform infrared (GATR-FTIR) spectroscopy, the APPJ-coated film composed mainly of inorganic SiO2 with traces of carbon derived from CH3 group, which makes the coating surface more hydrophobic. The subsequent oxidation process of APPJ or UV light leads to the decomposition of the methyl group at the surface. The antifouling properties of the PET surface against soil particulates deposited from air and their removal in aqueous detergent solution, were improved by APPJ-coating and subsequent APPJ-oxidation, respectively.
Polydimethylsiloxane (PDMS) is an extremely important and versatile polymeric material for biomedical and microfluidic devices due to a range of desirable properties. Control of the hydrophilicity of PDMS surfaces is of significant interest due to the potential for developing surfaces with tunable protein adsorption or cell adhesion properties. We report the formation of stable hydrophilic PDMS surfaces by covalent modification with glycans via aryldiazonium chemistry. The PDMS surface was modified by a two step-process including an activation of the PDMS surface, followed by reaction with aryldiazonium glycosides in aqueous solution. The functionalized PDMS was characterized by atomic force microscopy, infrared and X-ray photoelectron spectroscopy, water contact angle measurements and fluorescence microscopy. Our results demonstrate that glycans immobilized via this methodology have the dual function of imparting hydrophilicity and stabilizing the modified surface against hydrophobic recovery. Importantly, the presentation of thus immobilized glycosides makes them available to specific lectin-glycan binding interactions at the polymer-solution interface while, in the absence of specific binding interactions, leads to a reduction in albumin adsorption. This approach provides a novel and efficient route to stable hydrophilic PDMS surfaces with a broad range of applications.
In this work, an open-air arc plasma jet has been studied to polymerize 3-aminopropyelthrietoxysilane (APTES), which is the most commonly used aminosilane to functionalize surfaces with amine groups. Although the discharge produced from air is highly oxidative and the gas temperature is high as compared to other atmospheric plasma sources, amine groups, as well as amide ones, were identified in the nanometers thick coatings by XPS and FTIR analysis. By comparing the results with post-treatment and -grafting experiments, the partial retention of amine groups might be explained by the non-ideal mixing of the precursor flow with the main gas stream inside the plasma jet. Beside the intrinsic plasma reactivity, hydrodynamics effects are indeed important when considering flowing atmospheric plasmas.
This work describes a mathematical model for determining the power demand for a vertical shaft mowing machine, particularly taking into account the influence of speed on cutting power, which is different from that of other models of mowers. The influence of the apparatus' rotation and translation speeds was simulated in determining power demand. The results showed that no changes in cutting power were produced by varying the knives' angular speed (if translation speed was constant), while cutting power become increased if translation speed was increased. Variations in angular speed, however, influenced other parameters determining total power demand. Determining this vertical shaft mower's cutting pattern led to obtaining good crop stubble quality at the mower's lower rotation speed, hence reducing total energy requirements.
This study aimed to verify the influence of pH and temperature on the lysis of yeast using experimental design. In this study, the enzymatic extract containing β-1,3-glucanase and chitinase, obtained from the micro-organism Moniliophthora perniciosa, was used. The experiment showed that the best conditions for lysis of Pseudozyma sp. (CCMB 306) and Pseudozyma sp. (CCMB 300) by lytic enzyme were pH 4.9 at 37 ºC and pH 3.9 at 26.7 ºC, respectively. The lytic enzyme may be used for obtaining various biotechnology products from yeast.
Herein, the hydrophobic recovery of argon plasma treated polydimethylsiloxane surfaces is explored. In contrast to previous works, environmental contamination is here taken into account. We find that diffusion and reorientation strongly dominate the hydrophobic recovery under high thermal activation (60 °C), no matter the surrounding environment during storage. However, at lower temperature (24 °C and below), we find that contamination plays a major role in lab atmosphere environment. By working at low temperature and under inert nitrogen atmosphere to slow down the diffusion and reorientation dynamics and to avoid contamination, we identify two different temperature-dependent regimes in the kinetics of the hydrophobic recovery. One is fast and involves exclusively relaxation processes occurring in the surface region. The second, much slower, concerns diffusion phenomena in the sub-surface region. Thereby, the specific impact of bulk diffusion and surface reorientation processes can be distinguished during aging by slowing down the surface dynamics and by eliminating all possible sources of contamination.
This article attempts to give an overview of atmospheric plasma sources and their applications. The aim is to introduce, in a first part, the main scientific background concerning plasmas as well as the different atmospheric plasma sources (description, working principle). The second part focuses on the various applications of the atmospheric plasma technologies, mainly in the field of surface treatments.Thus this paper is meant for a broad audience: non-plasma-specialized readers will find basic information for an introduction to plasmas whereas plasma spectroscopists who are familiar with analytical plasmas may be interested in the synthesis of the different applications of the atmospheric pressure plasma sources.
There has been considerable interest in non-thermal atmospheric pressure discharges over the past decade due to the increased number of industrial applications. Diverse applications demand a solid physical and chemical understanding of the operational principals of such discharges. This paper focuses on the four most important and widely used varieties of non-thermal discharges: corona, dielectric barrier, gliding arc and spark discharge. The physics of these discharges is closely related to the breakdown phenomena. The main players in electrical breakdown of gases: avalanches and streamers are also discussed in this paper. Although non-thermal atmospheric pressure discharges have been intensively studied for the past century, a clear physical picture of these discharges is yet to be obtained.
This review surveys methods for the fabrication, by plasma surface treatments or plasma polymerization, of polymeric surfaces and thin plasma polymer coatings that contain reactive chemical groups useful for the subsequent covalent immobilization, by solution chemical reactions or vapor phase grafting, of molecules or polymers that can exert bio‐specific interfacial responses. Surfaces containing amine, carboxy, hydroxy, and aldehyde groups are the subject of this review. Aminated surfaces have been fabricated using various plasma vapors or mixtures and have found wide use for bio‐interface applications. However, in many cases the amine surfaces have a rather limited shelf life, with post‐plasma oxidation reactions and surface adaptation leading to the disappearance of amine groups from the surface. Aging is a widespread phenomenon that often has not been recognized, particularly in some of the earlier studies on the use of plasma‐fabricated surfaces for bio‐interfacial applications, and can markedly alter the surface chemistry. Plasma‐fabricated surfaces that contain carboxy groups have also been well documented. Fewer reports exist on hydroxy and aldehyde surfaces prepared by plasma methods. Hydroxy surfaces can be prepared by water plasma treatment or the plasma polymerization of alkyl alcohol vapors. Water plasma treatment on many polymer substrates suffers from aging, with surface adaptation leading to the movement of surface modification effects into the polymer. Both hydroxy and aldehyde surfaces have been used for the covalent immobilization of biologically active molecules. Aging effects are less well documented than for amine surfaces. This review also surveys studies using such surfaces for cell colonization assays. Generally, these surface chemistries show good ability to support cell colonization, though the effectiveness seems to depend on the process vapor and the plasma conditions. Carboxylate co‐polymer surfaces have shown excellent ability to support the colonization of some human cell lines of clinical interest. Immobilization of proteins onto plasma‐carboxylated surfaces is also well established.
XPS O/C ratios (0 ⁰ emission) as a function of storage time, of plasma‐polymerized methyl methacrylate deposited at power levels of 5 and 40 W.
magnified image XPS O/C ratios (0 ⁰ emission) as a function of storage time, of plasma‐polymerized methyl methacrylate deposited at power levels of 5 and 40 W.
Polydimethylsiloxane (PDMS) materials show the unique phenomenon that when exposed to electrical discharge, such as corona discharge, their hydrophobic surface becomes hydrophilic. However, after a certain relaxation time they gradually regain their hydrophobicity. In this study the adhesive force obtained by AFM force distance measurements using a hydrophilic Si3N4 probe is used to track the recovery of the hydrophobicity. The time constant of the recovery can be determined by measuring the adhesive force as a function of the recovery time after corona exposure. It is shown how these time constants can be used to monitor the recovery rate as a function of corona treatment time for both filled and unfilled PDMS compounds.
Poly(dimethyl siloxane) (PDMS) has been focused on recently due to its variety of applications specifically in microsystems technology. Many companies market two-component PDMS, which is comprised of a base component and a curing agent. Widely known and used for microsystems applications is Sylgard 184 from Dow Corning. Present work deals with two-component Room Temperature Vulcanized (RTV) PDMS from three different companies. They are Sylgard 184 from Dow Corning, RTV 615 from GE Silicones and RTV 141 from Rhodia Chemicals. Temporary increase in wettability of these three different types of PDMS by oxygen plasma by varying the plasma power and exposure time has been studied and compared with results available in literature. The hydrophobic recovery of the modified surfaces was monitored as a function of time and quantified. The surfaces were characterized using contact angle measurements and ATR-FTIR and XPS spectroscopy, their behavior analyzed in term of free surface energy and work of adhesion.
Polydimethylsiloxane (PDMS Sylgard 184, Dow Corning Corporation) pre-polymer was combined with increasing amounts of cross-linker (5.7, 10.0, 14.3, 21.4, and 42.9 wt.%) and designated PDMS1, PDMS2, PDMS3, PDMS4, and PDMS5, respectively. These materials were processed by spin coating and subjected to common micro-fabrication, micro-machining, and biomedical processes: chemical immersion, oxygen plasma treatment, sterilization, and exposure to tissue culture media. The PDMS formulations were analyzed by gravimetry, goniometry, tensile testing, nano-indentation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Spin coating of PDMS was formulation dependent with film thickness ranging from 308 microm on PDMS1 to 171 microm on PDMS5 at 200 revolutions per minute (rpm). Ultimate tensile stress (UTS) increased from 3.9 MPa (PDMS1) to 10.8 MPa (PDMS3), and then decreased down to 4.0 MPa (PDMS5). Autoclave sterilization (AS) increased the storage modulus (sigma) and UTS in all formulations, with the highest increase in UTS exhibited by PDMS5 (218%). PDMS surface hydrophilicity and micro-textures were generally unaffected when exposed to the different chemicals, except for micro-texture changes after immersion in potassium hydroxide and buffered hydrofluoric, nitric, sulfuric, and hydrofluoric acids; and minimal changes in contact angle after immersion in hexane, hydrochloric acid, photoresist developer, and toluene. Oxygen plasma treatment decreased the contact angle of PDMS2 from 109 degrees to 60 degrees. Exposure to tissue culture media resulted in increased PDMS surface element concentrations of nitrogen and oxygen.
Most of the silicone materials used for HV outdoor insulation are
high-consistency, heat cured polydimethylsiloxane (PDMS) elastomers. The
unique properties of PDMS that make it suitable for HV applications are
reviewed. The surface of these elastomers can be rendered hydrophilic by
exposure to discharges. A time and temperature dependent hydrophobic
recovery ensues when exposure ceases. A variety of surface
characterization investigations have established that corona exposure
forms a brittle, wettable, silica-like layer on the surface of most PDMS
elastomers. This is consistent with similar effects from oxygen and
inert gas plasma treatment. There is still considerable debate as to the
relative importance of the two major mechanisms postulated to account
for the hydrophobic recovery after corona discharge. The diffusion
mechanism invokes migration of low molecular weight species from the
interior to the surface, while the reorientation or overturn mechanism
envisages a surface reorganization with polar entities such as silanol
groups resulting from surface oxidation rotating away and being replaced
by methyl groups in the outermost surface layers. In our view, the
highly crosslinked silica-like layer cannot reorient readily between
hydrophilic and hydrophobic states at the surface, suggesting that
diffusion of low molecular weight PDMS components is the more important
mechanism of hydrophobic recovery. Recent data obtained on PDMS samples
free from low-molecular-weight diffusible species show that hydrophobic
recovery may be due to in-situ depolymerization
An issue in microfabrication of the fluidic channels in glass/poly (dimethyl siloxane) (PDMS) is the absence of a well-defined study of the bonding strength between the surfaces making up these channels. Although most of the research papers mention the use of oxygen plasma for developing chemical (siloxane) bonds between the participating surfaces, yet they only define a certain set of parameters, tailored to a specific setup. An important requirement of all the microfluidics/biosensors industry is the development of a general regime, which defines a systematic method of gauging the bond strength between the participating surfaces in advance by correlation to a common parameter. This enhances the reliability of the devices and also gives a structured approach to its future large-scale manufacturing. In this paper, we explore the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces. We find that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength. We obtained a good correlation between contact angle of deionized water (a direct measure of wettability) on the PDMS and glass surfaces based on various dosages or oxygen plasma treatment. The exposure was done first in an inductively coupled high-density (ICP) plasma system and then in plasma enhanced chemical vapor deposition (PECVD) system. This was followed by the measurement of bond strength by use or the standardized blister test.
Atmospheric-pressure plasmas are used in a variety of materials
processes. Traditional sources include transferred arcs, plasma torches,
corona discharges, and dielectric barrier discharges. In arcs and
torches, the electron and neutral temperatures exceed 3000°C and the
densities of charge species range from 1016-1019
cm-3. Due to the high gas temperature, these plasmas are used
primarily in metallurgy. Corona and dielectric barrier discharges
produce nonequilibrium plasmas with gas temperatures between
50-400°C and densities of charged species typical of weakly ionized
gases. However, since these discharges are nonuniform, their use in
materials processing is limited. Recently, an atmospheric-pressure
plasma jet has been developed, which exhibits many characteristics of a
conventional, low-pressure glow discharge. In the jet, the gas
temperature ranges from 25-200°C, charged-particle densities are 10
11-1012 cm-3, and reactive species are
present in high concentrations, i.e., 10-100 ppm. Since this source may
be scaled to treat large areas, it could be used in applications which
have been restricted to vacuum. In this paper, the physics and chemistry
of the plasma jet and other atmospheric-pressure sources are reviewed
This work reports a statistical study on the relationship between the chemical–physical properties of CNTs, which vary by changing the conditions of purification and plasma treatment, and the macroscopic properties of PC-based nanocomposites. CNTs are synthesized and then purified in two different ways and used as fillers for the preparation of PC/CNTs nanocomposites. In some cases, oxygen plasma treatment is carried out to improve their affinity to the matrix. The CNTs are characterized by TGA, ICP/OES, and FT-Raman spectroscopy, titration and morphological analysis. Mechanical, dynamic-mechanical, electrical, and morphological tests are used for characterizing PC/CNTs nanocomposites.
We have used two‐photon laser‐induced fluorescence to obtain quantitative measurements of the concentration of ground state O atoms in O2+CF4 rf discharges. Absolute calibration was achieved by generating a known concentration of atomic oxygen by UV laser photolysis of O2. Trace amounts of Ar were added to serve as an inert reference gas for concurrent optical emission measurements, in which the plasma‐induced optical emission intensities from O∗ and Ar∗ lines were recorded. Emission line shapes were measured using a Fabry–Perot interfermoter to gain information on the mechanisms for formation of excited oxygen atoms in the plasma. Two excitation mechanisms were found to be important: (1) electron impact excitation of ground state atoms, e+O → O∗+e, and (2) dissociative excitation of O2, e+O2 → O∗+O+e. Evidence for both excitation mechanisms was obtained for O∗ (8446 Å) emission, with atomic excitation being dominant, whereas dissociative excitation appeared to be the dominant mechanism for O∗ (7774 Å) emission. Argon actinometry for the determination of ground state oxygen was directly tested. Because of the contribution from dissociative excitation, a strict proportionality, O∗/Ar∗∝[O]/[Ar], was not satisfied where O∗ (Ar∗) is the intensity of an atomic oxygen (argon) emission line, and [O] ([Ar]) is the oxygen (argon) atom concentration. However, within certain limitations, the O∗ (8446 Å)/Ar∗ emission intensity ratio gives the right qualitative trends for the O atom concentration.
Plasma treatment of silicone surfaces is a useful way of increasing wettability to improve adhesion and a first step in producing various organosilicon thin-film composites. Despite numerous earlier studies, there is no consensus on the effect of plasma treatment nor on the mechanism of the subsequent hydrophobic recovery. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to study the effect of plasma treatments of polydimethylsiloxane elastomer using four different plasma gases: argon, helium, oxygen, and nitrogen. In each case, the surface was oxidized to produce a thin, wettable, brittle silica-like layer. These surfaces progressively recover their hydrophobicity by diffusion of untreated polymer chains through cracks in the treated layer. Angle-resolved XPS detected the untreated, diffused layer and SEM revealed the common occurrence of cracks in the treated layer, although conditions could be found for each gas where the surface becomes completely wettable by water but is free from cracks.
Silicone rubber films were surface-modified with O2, Ar, or NH3 plasma in either a bell-jar-type or a tubular-type reactor to investigate the effect of the plasma treatment conditions on the hydrophilicity, peel strength, and chemical composition of the film surface. ESCA spectra of the modified films were used to calculate the elemental ratios of oxygen to carbon and nitrogen to carbon. In the bell-jar-type reactor, the order of hydrophilicity improvement was found to be O2 > Ar > NH3 plasma. NH3 plasma treatment at 10 W for 2 min resulted in the highest enhancement of peel strength. The contact angle of water on the modified surface increased with storage humidity. However, the peel strength decreased with the storage time.
Crosslinked polydimethylsiloxane (PDMS) containing Irganox® 1076, Tinuvin® 770 or Irganox® 565, prepared by swelling PDMS in a solution of one of these stabilizers in n-hexane, was exposed to a corona discharge and the corona exposure time (τcrit) to form a brittle, silica-like layer was determined by optical microscopy. The critical corona exposure time showed a linear increase with increasing stabilizer concentration; Tinuvin 770 showed the highest efficiency and Irganox 1076 the lowest. The increase in τcrit on corona exposure of the stabilized samples with reference to the value for unstabilized PDMS was similar to that reported earlier for air plasma exposed samples. The efficiency of the stabilizers towards corona-induced surface oxidation of PDMS was also confirmed by X-ray photoelectron spectroscopy.
To control the interactions between surfaces and biological systems, it is common to attach polymers, proteins, and other species to the surfaces of interest. In this case, surface modification of polydimethylsiloxane (PDMS) was performed by exposing PDMS films to the effluent from a microwave ammonia plasma, with a goal of creating primary amine groups on the PDMS. These amine sites were to be used as binding sites for polymer attachment. Chemical changes to the surface of the PDMS were investigated as a function of treatment time, microwave power, and PDMS temperature during plasma treatment. Functional groups resulting from this treatment were characterized using attenuated total reflectance infrared spectroscopy. Plasma treatment resulted in the incorporation of oxygen- and nitrogen-containing groups, including primary amine groups. In general, increasing the treatment time, plasma power and substrate temperature increased the level of oxidation of the films, and led to the formation of imines and nitriles. PDMS samples treated at 100 W and 23 °C for 120 s were chosen for proof-of-concept dextran coating. Samples treated at this condition contained primary amine groups and few oxygen-containing groups. To test the viability of the primary amines for attachment of biopolymers, functionalized dextran was successfully attached to primary amine sites on the PDMS films.
We report an experimental study of the surface modification of polydimethylsiloxane (PDMS) by atmospheric pressure plasma (APP). The contact angle of a water droplet, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) were used to analyze the modified surface and the hydrophilic stability of PDMS samples, which were mixed with different ratios of base polymer and curing agent. The modified hydrophilic surface of PDMS lasted for 20days, the duration of our experiment. In FTIR analysis, a broad peak at 3420cm−1 appeared after plasma treatment for 15s, which corresponded to hydroxyl group formation on the PDMS surface during plasma treatment. Another new finding is that the magnitude of the peak for PDMS-05, which contained excess curing agent, was the smallest among the PDMS samples. Thus, the plasma treatment modifies the surface of the PDMS by adding hydroxyl groups and the resulting hydrophilic surface depends on the ratio of base polymer to curing agent. Moreover, SEM analysis showed that the bare PDMS-05 sample had a cracked surface, while the bare PDMS-20 was relatively smooth. This cracked or rough topology of the bare PDMS decreased with increased base polymer on reducing amount of curing agent. This improvement in the surface roughness of the plasma-treated samples may be caused by a shallow etching process that occurs during plasma treatment with oxygen gas. It constitutes an effective method for modifying the surface of PDMS without specific skills, expensive apparatus, or clean-room facilities.
Low-pressure plasma treatment has been demonstrated to be suitable to increase the surface energy and adhesion of synthetic sulfur-vulcanized styrene-butadiene (R2) rubber. Although effective, this treatment required vacuum and it is relatively expensive for some industrial applications, mainly in footwear and construction. In this study, the atmospheric pressure treatment of a difficult to bond sulfur-vulcanized R2 rubber by means of a plasma torch system was proposed. Two distances between the R2 rubber and the plasma torch nozzle (0.5 and 1cm), and the time of treatment were varied, and their influence on the rubber surface modifications produced has been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been obtained from T-peel tests of surface-treated R2 rubber/polyurethane adhesive joints. The wettability was improved by decreasing the rubber–plasma torch nozzle distance because a partial removal of paraffin wax from the rubber surface was produced. On the other hand, the R2 rubber surface was oxidized by the plasma torch treatment. The longer the time of the plasma torch treatment, the higher the degree of surface oxidation (mainly C–O moieties were produced). Although the R2 rubber surface was effectively modified by the plasma torch treatment, the adhesion to polyurethane adhesive was not greatly improved, due to the migration of paraffin wax to the treated R2 rubber–polyurethane adhesive interface once the adhesive joint was produced. On the other hand, the extended treatment with plasma torch enhanced the level of the migration of zinc stearate to the rubber–polyurethane adhesive interface, contributing to deteriorate the adhesion in greater extent.
Plasma-surface modification (PSM) is an effective and economical surface treatment technique for many materials and of growing interests in biomedical engineering. This article reviews the various common plasma techniques and experimental methods as applied to biomedical materials research, such as plasma sputtering and etching, plasma implantation, plasma deposition, plasma polymerization, laser plasma deposition, plasma spraying, and so on. The unique advantage of plasma modification is that the surface properties and biocompatibility can be enhanced selectively while the bulk attributes of the materials remain unchanged. Existing materials can, thus, be used and needs for new classes of materials may be obviated thereby shortening the time to develop novel and better biomedical devices. Recent work has spurred a number of very interesting applications in the biomedical field. This review article concentrates upon the current status of these techniques, new applications, and achievements pertaining to biomedical materials research. Examples described include hard tissue replacements, blood contacting prostheses, ophthalmic devices, and other products.
The aim of this study was the creation of a silicone hydrophilic
surface prior to bonding. Modifications in wettability and adhesion
properties of silicone were performed with an atmospheric plasma
torch (APPT). Surface energy variations of the substrate, both
pristine and APPT-treated, were evaluated through contact angle
measurements, studying the hydrophobic recovery of the samples
up to 24 hours of aging. Compositional and topographical changes
induced by APPT and aging were studied by attenuated total
multiple reflection mode infrared spectroscopy (ATR-FTIR), X-ray
photoelectron spectroscopy (XPS), mechanical profilometry, scanning
electron microscopy (SEM), and atomic force microscopy
(AFM), respectively. Adhesion pull-off tests were performed on
silicone-aluminium stud joints using three commercial adhesives,
which were Sikaflex1-252, polyurethane-based, Loctite1-330,
urethane methacrylate ester-based acrylic, and Terostat1-922,
modified silicone. Although experimental data of all the bonding
specimens led to an undesired adhesive failure, it was found that
APPT-treated samples gave higher adhesive strength than the
pristine ones, which was explained by the higher surface energy,
thus more wettable material, after APPT. This effect remained stable
for just 1 h, when the substrate began its hydrophobic recovery,
reaching the original surface energy values after 24 h of aging.
Currently, there is a strong tendency to replace rigid electronic assemblies by mechanically flexible and stretchable equivalents. This emerging technology can be applied for biomedical electronics, such as implantable devices and electronics on skin. In the first step of the production process of stretchable electronics, electronic interconnections and components are encapsulated into a thin layer of polydimethylsiloxane (PDMS). Afterwards, the electronic structures are completely embedded by placing another PDMS layer on top. It is very important that the metals inside the electronic circuit do not leak out in order to obtain a highly biocompatible system. Therefore, an excellent adhesion between the 2 PDMS layers is of great importance. However, PDMS has a very low surface energy, resulting in poor adhesion properties. Therefore, in this paper, PDMS films are plasma treated with a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0 kPa). Contact angle and XPS measurements reveal that plasma treatment increases the hydrophilicity of the PDMS films due to the incorporation of silanol groups at the expense of methyl groups. T-peel tests show that plasma treatment rapidly imparts adhesion enhancement, but only when both PDMS layers are plasma treated. Results also reveal that it is very important to bond the plasma-treated PDMS films immediately after treatment. In this case, an excellent adhesion is maintained several days after treatment. The ageing behaviour of the plasma-treated PDMS films is also studied in detail: contact angle measurements show that the contact angle increases during storage in air and angle-resolved XPS reveals that this hydrophobic recovery is due to the migration of low molar mass PDMS species to the surface.
Silicone elastomers were surface modified by oxygen microwave plasma under different conditions and the elemental composition was followed by X-ray photoelectron spectroscopy (XPS). The changes in elemental composition were mapped by a method based on ternary XPS diagrams that we have recently developed. Already at the shortest treatment times, 5 s, the change in surface composition is more than one-half the maximum change obtained on prolonged exposure. After this initial change, the surface gradually oxidizes toward the final composition. Curve resolutions of C1s and Si2p XPS data showed that the initial jump in surface composition is caused by an oxidation of silicon where one of the two methyl groups are replaced by an oxygen. The second methyl group appears to be more difficult to remove, but as the treatment progresses, the number of oxygen bonded to silicon gradually increases. The dominating form of carbon acts as unoxidized methyl groups throughout the process, but the total carbon percentage decreases as the treatment progresses. This indicates either that the methyl groups are removed without prior oxidation or that the methyl groups are removed shortly after oxidation. A silica-like surface layer was formed on prolonged plasma treatment under all the investigated conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4098–4104, 2004
Silicon oxide based (SiO(x)C(y)H(z), noted SiO(x)) coatings are often used in surface engineering for microelectronics, corrosion resistance, barrier to gas permeation through polymeric materials, etc ... SiO(x) coatings can be efficiently deposited by non-equilibrium atmospheric pressure plasma processes, such as DBD or plasma jets. In the present study, the design of experiment (DoE) methodology was used to investigate the influence of process parameters on the characteristics of organosilicon coatings deposited by a non-equilibrium atmospheric pressure plasma jet (APPJ) from hexamethyldisiloxane (HMDSO) and air mixtures. The results obtained were used to create an empirical model to predict the chemical composition of coatings. Among 11 process parameters, the 3 parameters which exhibited the strongest effect on the coating composition were the torch speed, the substrate to nozzle distance and the number of scans. Auger spectroscopy revealed that the carbon content of the thin films was as low as 6 +/- 1.7% and AFM analysis showed that smooth coatings (R(a) similar to 2 nm) were obtained even at high dynamic growth rates (similar to 1 000 nm.m.min(-1)). A tentative macroscopic scaling law was also formulated to correlate our results with the available literature data.
Silicone rubber is suitable for the thermal insulator of the rocket motors owing to its heat resisting properties as well as its excellent elasticity and restoring force. However, the adhesion properties of the silicone rubber should be improved greatly to be used as the thermal insulator because of its poor adhesiveness coming from the low surface tension. Functional groups were incorporated through copolymerization to the silicone rubber to induce chemical reaction with the functional groups in the propellant/liner components to enhance the adhesion properties. Peeling tests results disclosed that the incorporation of amine groups was the most efficient for the adhesiveness enhancement and that addition of carbon black improved the adhesiveness still more. Stability against thermal degradation of the silicone rubber was examined by measuring the activation energy through the thermogravimetric analysis. The results revealed that the compounding of the Cloisite® clays boosted up the thermal stability of the silicone rubber much more greatly than that of carbon black. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2782–2787, 2007
The role of the active species involved in the superficial modification of natural and manmade fibers is discussed for the example of wool and PA6 fabrics treated by means of post‐discharge plasmas (N 2 , N 2 + 23% O 2 , O 2 ) to avoid UV radiation, ions, electrons and other species present in direct plasma discharges. The active species present in the N 2 post‐discharge have been quantitatively and qualitatively evaluated by means of optical emission spectroscopy. Their action on the surface of the fibers has been analyzed by dynamic contact angle, revealing an improved wettability that has been attributed to the generation of new chemical groups and the reduction/elimination of the fatty layer on the surface of wool.
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Plasma treatments are widely used to activate polymer surfaces prior to adhesive bonding.
This study investigates the influence of plasma treatment conditions on the surface activation
of a range of polymers using the PlasmaTreat (Open Air) system. In this study the effect of dc pulse plasma cycle time, compressed air flow rate and the plasma jet nozzle to substrate
distance on the plasma discharge was examined. The influence that the dc pulse plasma cycle time parameter has on the activation of polypropylene, polystyrene and polycarbonate was also investigated. The level of polymer surface activation was evaluated based on the change in water contact angle after plasma treatment. The polymer surface properties were also monitored using AFMand XPS measurements. The heating effect of the plasma was monitored using both infrared thermographic camera and thermocouple measurement s. Plasma diagnostics measurements were obtained using the photodiode and optical emission spectroscopy techniques. From this study it was concluded that for the Plasma-
Treat system the level of plasma activation was closely correlated with the dc pulsed plasma cycle time, which is a measure of the plasma intensity. For example, the more intense plasma obtained with shorter cycle times gave higher levels of polymer activation. The optimized pulsed plasma cycle times were found to be specific for a given polymer type and related to their thermal properties. The pulsed cycle times were also found to correlate with both the substrate and plasma gas temperatures.
Silicon rubber, PDMS, was irradiated by Ar, Ar/H2 and Ar/O2 plasmas to increase the surface wettability to water which was found to increase with the irradiation time for every application of plasma irradiation. The use of Ar/O2 plasma was found to be particularly effective in enhancing the surface wettability. The aging behavior due to exposure to air, ethanol or water was also measured. In the case of continuous exposure to water after plasma treatment, the wettability could be maintained for more than several months with the water immersion.
This paper reviews methods of modifying polydimethylsiloxane (PDMS) polymers to improve their properties for biomedical applications. The modification methods are discussed under three different categories: bulk, surface and other modification techniques. Surface modification techniques include physical and chemical techniques to modify polymer surfaces. Bulk modification techniques include blending, copolymerization, interpenetrating polymer networks (IPNs) and functionalization. The third category includes less common modification techniques.
© 2001 Society of Chemical Industry
In this paper, a remote DC glow discharge at atmospheric pressure is employed for surface modification of PDMS aimed at improvement of its adhesive properties. The effects of the discharge on the surface properties of PDMS are probed using contact angle measurements, XPS and T-peel tests. Results show that the DC glow discharge transforms the initially hydrophobic PDMS surface into a hydrophilic one due to the incorporation of silanol groups at the expense of methyl groups. Moreover, T-peel tests confirm that the remote DC glow plasma is able to remarkably enhance the adhesion between two PDMS layers, but only when both layers are plasma-treated.
The polymers PET, PA6, PVDF, HD-PE, and PP are activated by a commercially available plasma jet system at atmospheric pressure to improve adhesive bondability. The adhesion properties of the activated surfaces are evaluated by lap shear tests. The results are correlated with the surface properties that are investigated by XPS, AFM, and contact angle measurements. In addition the influence of operational parameters of the plasma treatment is studied. The activated samples exhibit a substantially increased bonding strength. The improvement can be related to an increase of oxygen concentration, and to changes of the topology of the substrate surface induced by the thermal component of the plasma. The most influential parameters in the plasma treatment are the distance between substrate and nozzle exit and the treatment time.
The cellular adhesion and motility have direct implications in the tumoral-metastatic cells development or in the tissue engineering mechanisms for instance. Our work aims at knowing the impact of substrate mechanical properties on those adhesion and motility mechanisms by modifying bulk rigidity, surface energy and composition of a bio-compatible poly-di-methyl-siloxane (PDMS) substrate. We show how a wide range of PDMS rigidity can be obtained and how Ar/O2-based plasmas turn PDMS surface to hydrophilic. A correlation between surface energy, bulk rigidity, cells adhesion and growth is finally shown.
Spin-coated specimens of crosslinked polydimethylsiloxane (PDMS) exposed to radio-frequency (RF) and microwave (MW) oxygen plasma were studied by specular neutron reflectometry, X-ray photoelectron spectroscopy (XPS), Wilhelmy balance, contact angle measurements, scanning electron microscopy and atomic force microscopy. Neutron reflectometry and XPS showed that the oxygen plasma led to the formation of a smooth (<10 nm), oxidised surface layer with a thickness of 130–160 nm. The oxidised layer contained a mixture of the original polymer and silicon bonded to three or four oxygen atoms (SiOx). The oxidised layer was thinner after longer plasma exposure, indicating a decrease in specific volume due to a conversion of the polymer structure to an inorganic SiOx-rich structure. The formation of the SiOx-containing layer with low segmental mobility was further confirmed by the small hysteresis in the Wilhelmy balance measurements. The similarity in the hydrophobicity recovery kinetics of specimens aged in dry air, dry argon and vacuum and XPS data showed that the hydrophobicity recovery is not due to contamination through adsorption from the atmosphere but due to migration of low molar mass PDMS species to the surface. Scanning electron microscopy also showed the presence of surface cracks in heavily oxidised specimens.
The influence of temperature, water activity and pH on the time necessary for germination of 90% of Penicillium chrysogenum conidia inoculated (T90) was determined.
A new experimental device was developed for easy monitoring of the germination process. Experiments were carried out according to a Doehlert matrix at 11-31 degrees C, 0.86-0.98 water activity (a(w)) and pH 3.5-6.5. In these conditions, a second order polynomial relationship between T90 and the environmental factors was established for the different humectants used throughout this study (e.g. glycerol and sorbitol) with regression coefficients close to 0.97.
For both humectants, the major effect of temperature and water activity on T90 was highlighted, whereas the effect of pH on T90 in these experimental conditions was not significant. The combined effect of temperature and water activity on T90 was also demonstrated.
Both the experimental set-up and the Doehlert matrix were well suited to determine the influence of environmental factors on mould germination.
Medical-grade polydimethylsiloxane elastomer was subjected to low-powered plasma treatment in the presence of four different gases: O(2), Ar, N(2) and NH(3). Changes to the surface chemistry immediately after processing and the stability of the treatments following ageing in phosphate buffered saline or air for up to 1 month were investigated using X-ray photoelectron spectroscopy and dynamic contact angle analysis. Changes in surface morphology were assessed using optical microscopy and atomic force microscopy. All treatments resulted in an increase in wettability, attributed to major changes in chemistry combined with modest etching. Furthermore, the primary site of attack of the plasma species appeared to be dependent upon the feed gas implemented. The two main chemical changes observed after ageing were due to reactions with the storage media and relaxation processes resulting in further changes in wettability. The influence of the surface modifications on the blood compatibility of the materials was investigated by assessing contact phase activation using a partial thromboplastin time assay. It was demonstrated that the O(2) and Ar plasma treatments reduced the performance of the silicone but the N(2) and NH(3) treatments had a significantly beneficial effect on the activation of the coagulation cascade.
We describe a method based on plasma polymerization for the modification and control of the surface properties of poly(dimethylsiloxane) (PDMS) surfaces. By depositing plasma polymerized acrylic acid coatings on PDMS, we succeeded to fabricate stable (several days) hydrophilic and patterned hydrophobic/hydrophilic surfaces. We used this approach to generate direct and (for the first time in this material) double emulsions in PDMS microchannels.
Water repellency, high surface resistivity, vandalism resistance,
low density and good processability have made silicone rubbers based on
polydimethylsiloxane (PDMS) very attractive materials in housings for
outdoor insulation. Their ability to recover hydrophobicity after
oxidation or contamination is of paramount importance and this is the
topic of this review. A critical evaluation of the chemical and physical
mechanisms responsible for hydrophobicity loss and recovery is presented
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