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Heterogeneous Silicone Nanorods with Region-Specific Functionality
Abstract
Region-selective chemical modification of nano- and microstructures can unlock a world of novel functional surfaces. However, this small scale makes region selectivity challenging, especially on homogeneous and chemically inert synthetic structures. Here, we report the one-step in situ dynamic synthesis of heterogeneous multicomponent hybrid silicone nanorods (MCH-SNRs). These nanorods bear specific modifiable regions that can be assigned to different positions on-demand and selectively functionalized via a photoinitiated, radical-based thiolene click reaction. The distribution of different constituent components with desired properties hinges on the independent growth of the individual segment of the bamboo-shaped structure, which can be tailored by using different precursors under specific reaction conditions. Region selectivity of the functionalization is validated by exploiting wetting transitions along bamboo segments, visualized by confocal microscopy.
... Low surface energy superhydrophobic materials with an excellent water-repellent surface have the potential to enable a wide range of functions [1], including self-cleaning [2], anti-fogging [3], antibacterial [4], oil-water separation [5], water harvesting [6], and anticorrosion [7]. Surface coating techniques are a common method to achieve superhydrophobicity, creating micro/nanostructures using materials of low surface tension [8]. Most engineering materials, including pure metals, alloys, ceramics, and semiconductors, are inherently hydrophilic. ...
... The last term in equation (8) represents the enthalpy contribution in the original Flory-Huggins theory and can be positive or negative, depending on the value of χ. The first two terms of equation represent the combinatorial entropy contribution and are always negative. ...
A droplet deposited on a solid substrate leads to the wetting phenomenon. A natural observation is the lotus effect known for its superhydrophobicity. This special feature is engendered by the structured microstructure of the lotus leaf, namely, surface heterogeneity, as explained by the quintessential Cassie-Wenzel theory. In this work, recent designs of functional substrates are overviewed based on the Cassie-Wenzel theory via manipulating the contact area between the liquid and the solid substrate as well as the intrinsic Young's contact angle. Moreover, the limitation of the Cassie-Wenzel theory is discussed. When the droplet size is comparable to the surface heterogeneity, anisotropic wetting morphology often appears, which is beyond the scope of the Cassie-Wenzel work. In this case, several recent studies addressing the anisotropic wetting effect on chemically and mechanically patterned substrates are elucidated. Surface designs for anisotropic wetting morphologies are summarized with respect to the shape and the arrangement of the surface heterogeneity, the droplet volume, the deposition position of the droplet, as well as the mean curvature of the surface heterogeneity. A thermodynamic interpretation for the wetting effect and the corresponding open questions are presented at the end. This article is protected by copyright. All rights reserved.
Recently, the demand and studies related with Multi-Material Additive Manufacturing (MMAM) is continuously increasing. To uncover the essential knowledge hidden in the current mess of research works, this study, based on a simple review methodology, helps to identify and discuss the current knowledge about: limitations of software and hardware, the interface bonding strength of dissimilar materials, polymer reinforcement with continuous fiber, polymer-based multi-materials, and future and challenges. The review method starts with a list of topics to check: MMAM of polymers, the bonding strength between materials, knowledge gaps, and new development lines in polymer applications. Then, it continues with the search procedure on electronic databases and the inclusion and exclusion criteria definition. Finally, to help the discussion and assessment, the information is collected in tables.
The functional surface features of living creatures are driven by the complex morphology of periodically arranged micro/nanoscale structures. Various fabrication processes have been devised mimic the performance of natural features; these methods morph hierarchical and multi‐leveled pillar arrays, such as top‐down, bottom‐up, and a hybrid of top‐down and bottom‐up processes. Different methodologies are employed depending on the materials, such as polymeric composites, metal oxides, metals, and carbon nanotubes. In this review, we discuss the shape‐reconfiguration of stimuli‐responsive micro/nanopillar arrays achieved by capillary force, light, magnetic field, and heat. In particular, photo‐ and magnetic actuation of pillar arrays revealed programmability according to the arrangement of the liquid crystal molecules or magnetic particles by remote control. Furthermore, applications of micro/nanopillar arrays, such as adhesives, omniphobicity, optics, and biomedical technologies, are also discussed.
Controlling the arrangement and interface of nanoparticles is essential to achieve good transfer of charge, heat, or mechanical load. This is particularly challenging in systems requiring hybrid nanoparticle mixtures such as combinations of organic and inorganic materials. This work presents a process to coat vertically aligned carbon nanotube (CNT) forests with metal oxide nanoparticles using microwave‐assisted hydrothermal synthesis. Hydrothermal processes normally damage delicate CNT forests, which is addressed here by a combination of lithographic patterning, transfer printing, and reduction of the synthesis time. This process is applied for the fabrication of structured Li‐ion battery (LIB) electrodes where the aligned CNTs provide a straight electron transport path through the electrode and the hydrothermal coating process is used to coat the CNTs with conversion anode materials for LIBs. These nanoparticles are anchored on the surface of the CNTs and batteries fabricated following this process show a fourfold longer cyclability. Finally, this process is used to create thick electrodes (350 µm) with a gravimetric capacity of over 900 mAh g⁻¹.
Superhydrophobic surfaces are usually assumed to be rigid so that liquids do not deform them. Here we analyze how the relation between microstructure and wetting changes when the surface is flexible. Therefore we deposited liquid drops on arrays of flexible micropillars. We imaged the drop's surface and the bending of micropillars with confocal microscopy and analyzed the deflection of micropillars while the contact line advanced and receded. The deflection is directly proportional to the horizontal component of the capillary force acting on that particular micropillar. In the Cassie or “fakir” state, drops advance by touching down on the next top faces of micropillars, much like on rigid arrays. In contrast, on the receding side the micropillars deform. The main force hindering the slide of a drop is due to pinning at the receding side, while the force on the advancing side is negligible. In the Wenzel state, micropillars were deflected in both receding and advancing states.
Mesoscale heterogeneous material systems are efficient and adaptive to real world environments, owing to the non-uniform stress fields that result from the convolution of component geometries, loading conditions, and environmental changes. With the advent of multi-material additive manufacturing, the production of heterogeneous material systems with a pre-defined mesoscale material distribution becomes feasible. This unlocks the design freedom at a characteristic length scale between the macroscale geometry and microstructures, but also calls for a new design framework to optimize the mesoscale material distribution in multi-material additive manufacturing. Here, we propose and demonstrate such a design framework by incorporating digital image correlation-based deformation mapping with 3D finite element modeling-based computational optimization. The constitutive behavior of each constituent material or their mixtures is calibrated by matching the local deformation data. The optimal mesoscale material distribution can then be determined using global optimization algorithms and validated experimentally.
Intelligent application of materials with site-specific properties will undoubtedly allow more efficient components and use of resources. Despite such materials being ubiquitous in nature, human engineering structures typically rely upon monolithic alloys with discrete properties. Additive manufacturing, where material is introduced and bonded to components sequentially, is by its very nature a good match for the manufacture of components with changes in property built-in. Here, some of the recent progress in additive manufacturing of material with spatially varied properties is reviewed alongside some of the challenges facing and opportunities arising from the technology.
Superliquid repellency can be achieved by nano- and microstructuring surfaces in such a way that protrusions entrap air underneath the liquid. It is still not known how the three-phase contact line advances on such structured surfaces. In contrast to a smooth surface, where the contact line can advance continuously, on a superliquid-repellent surface, the contact line has to overcome an air gap between protrusions. Here, we apply laser scanning confocal microscopy to get the first microscopic videos of water drops advancing on a superhydrophobic array of micropillars. In contrast to common belief, the liquid surface gradually bends down until it touches the top face of the next micropillars. The apparent advancing contact angle is 180°. On the receding side, pinning to the top faces of the micropillars determines the apparent receding contact angle. Based on these observations, we propose that the apparent receding contact angle should be used for characterizing superliquid-repellent surfaces rather than the apparent advancing contact angle and hysteresis.
Interest in multifunctional structures made automatically from multiple materials poses a challenge for today's additive manufacturing (AM) technologies; however the ability to process multiple materials is a fundamental advantage to some AM technologies. The capability to fabricate multiple material parts can improve AM technologies by either optimising the mechanical properties of the parts or providing additional functions to the final parts. The objective of this paper is to give an overview on the current state of the art of multiple material AM technologies and their practical applications. In this paper, multiple material AM processes have been classified and the principles of the key processes have been reviewed comprehensively. The advantages and disadvantages of each process, recent progress, challenging technological obstacles, the possible strategies to overcome these barriers, and future trends are also discussed.
A facile and versatile method for creating superhydrophilic patterns in superhydrophobic porous polymer films by UV-initiated photografting is presented. The extreme difference in wettability between superhydrophilic and superhydrophobic areas allows the use of the superhydrophilic patterns as virtual microfluidic channels. The method allows for precise control of the size and geometry of photografted superhydrophilic features, and the thickness, morphology, and transparency of the superhydrophobic and hydrophobic porous polymer films.
The wetting of rough surfaces remains a subject of active investigation by scientists. The contact angle (CA) is a traditional parameter used to characterize the hydrophobicity/philicity of a solid surface. However, it was found recently that high CAs can coexist with strong adhesion between water and a solid surface in the case of the so-called 'rose petal effect'. Several additional parameters have been proposed to characterize the interaction of water with a rough solid surface, including the CA hysteresis, the ability of water droplets to bounce off a solid surface, the tilt angle needed to initiate the flow of a droplet, and the normal and shear adhesion. It is clear now that wetting is not characterized by a single parameter, since several modes or regimes of wetting of a rough surface can exist, including the Wenzel, Cassie, lotus and petal. Understanding the wetting of rough surfaces is important in order to design non-adhesive surfaces for various applications.
Mesoscale hierarchical helical structures with diverse functions are abundant in nature. Here we show how spontaneous helicity
can be induced in a synthetic polymeric nanobristle assembling in an evaporating liquid. We use a simple theoretical model
to characterize the geometry, stiffness, and surface properties of the pillars that favor the adhesive self-organization of
bundles with pillars wound around each other. The process can be controlled to yield highly ordered helical clusters with
a unique structural hierarchy that arises from the sequential assembly of self-similar coiled building blocks over multiple
length scales. We demonstrate their function in the context of self-assembly into previously unseen structures with uniform,
periodic patterns and controlled handedness and as an efficient particle-trapping and adhesive system.
Superhydrophobic surfaces have drawn a lot of interest both in academia and in industry because of the self-cleaning properties. This critical review focuses on the recent progress (within the last three years) in the preparation, theoretical modeling, and applications of superhydrophobic surfaces. The preparation approaches are reviewed according to categorized approaches such as bottom-up, top-down, and combination approaches. The advantages and limitations of each strategy are summarized and compared. Progress in theoretical modeling of surface design and wettability behavior focuses on the transition state of superhydrophobic surfaces and the role of the roughness factor. Finally, the problems/obstacles related to applicability of superhydrophobic surfaces in real life are addressed. This review should be of interest to students and scientists interested specifically in superhydrophobic surfaces but also to scientists and industries focused in material chemistry in general.
While partial wetting at nano-/microstructured surfaces can be described using the intermediate wetting state between the Cassie-Baxter and Wenzel states, the limitations of the partial wetting model remain unclear. In this study, we performed surface free energy analysis at a microstructured Si-water interface from both theoretical and experimental viewpoints. We experimentally measured the water contact angle on microstructured Si surfaces with square holes and compared the measured values with theoretical predictions. Furthermore, the surface free energy was analyzed using the effective wetting area estimated from the measured contact angle and electrochemical impedance spectroscopy results. We verified the validity of the partial wetting model for fabricated Si surfaces with a hole aperture a less than 230 μm and a hole height h of 12 μm, and for a < 400 μm, h = 40 μm. The model was found to be applicable to microstructured Si surfaces with a/h < 10.
Dynamically Shaped Stiff Nanorods In article number 2203820, Stefan Seeger and co‐workers propose a dynamic droplet assisted growth and shaping (d‐DAGS) synthesis strategy for the one‐step synthesis and in‐situ control of the shape of nanostructures. The obtained bamboo‐shaped silicone nanorods exhibit highly‐regular and tunable structure with ultra‐high aspect ratio, present robust mechanical stiffness and chemical durability, and can be used for various practical applications.
Micro/nano functional devices featuring deep integration, intelligence, and miniaturization have attracted considerable attention in frontier areas of research, such as micro/nano optics, micro/nano sensors, micro-electromechanical systems, and biomedicine. However, traditional micro/nano fabrication techniques, such as lithography, electrodeposition, etching, and laser microfabrication show inferior capability for manufacturing micro/nano structures with sophisticated geometries and multi-materials. Additive manufacturing (AM) is an advanced manufacturing process that offers great freedom in fabricating highly sophisticated structures over a wide length scale—from nanometers to millimeters. AM technology provides multi-scale, multi-material, and multi-dimensional manufacturing abilities for micro/nano functional devices, greatly advancing their development and applications. In this paper, a comprehensive review of recent advances in the AM of micro/nano functional devices is provided. Functional materials for micro/nano AM are also summarized. Micro/nano AM techniques, as well as fabricated micro/nano functional devices, are highlighted. Finally, limitations of the current investigations are discussed, and a future envision of multiple micro/nano functional devices is proposed. We hope that this review will provide a formwork of micro/nano functional devices fabricated by AM, which could offer a destination board to researchers interested in this area.
Polymeric composites with multi-functionality offer significant advantages over metals, including lightweight, high strength and stiffness, corrosion and fatigue resistance, etc. Additively manufactured composites draw intensive attention over the past decade due to that they exhibit the large potential to extend their applications from rapid prototyping to functional end-use components. Moreover, advances in additive manufacturing (AM) open new perspectives for the next generation of design and manufacturing of composites, which possess spatially digitalized and materialized arrangement of material/structure in a voxel-by-voxel manner. This review examines the work performed in this fast-growing field and elaborates its future perspectives and potentials. Specifically, the polymer AM processes incorporating different types of reinforcements are discussed in terms of mechanism, feedstocks, their advantages, and constraints. Then, the AM-driven designs for polymeric composites on multiscale and for multi-functional applications are emphasized. Further, emerging research topics including digital composites, intelligence/data-driven design approaches, and four-dimensional printing are further addressed with the careful analysis of existing gaps and future research trends. Finally, this review is concluded with an outlook on future research opportunities on AM-fabricated composites from design to fabrication. This review aims to provide a comprehensive guide to the stakeholders who want to utilize or develop an AM process for polymeric composites.
The divergences in superwettability between lotus leaves and rose petals result from minute differences in their morphological features. The fabrication of these hierarchical structures with unique wetting behaviors is fascinating but challenging. In this paper, a simple and cost-effective approach for controllable fabrication of hierarchical surfaces is presented. Two kinds of hierarchical polymethyl methacrylate (PMMA) structures, including microhemispherical and micropillar arrays covered with nanowires, were obtained by directly molding from anodic aluminum oxide (AAO) templates using UV lithography and two anodization steps. Multiscale structural features and surface chemical compositions influenced the adhesiveness of water droplets to the surfaces. The surface morphologies were precisely controlled by regulating the anodization condition of the AAO templates. The hierarchical surface with either a microhemispherical or micropillar array exhibits excellent hydrophobicity. Surfaces bearing micropillar arrays with –COOH modification show a rose petal effect but switch to a lotus effect after fluorination of the surface. In contrast, surfaces bearing microhemisphere arrayed hierarchical structures always show a rose petal effect, independent of the chemical composition of the surfaces. The controllable fabrication of surfaces with different wettability behaviors and switching between the lotus and rose petal effect is important for the design and fabrication of surfaces with desired properties.
The preparation of superhydrophobic coatings has been extensively researched, but their practical applications are limited by complicated preparation processes and poor mechanical durability. This study proposed a simple, low-cost method of preparing superhydrophobic coatings. A nano-silica dispersion was sprayed onto a semi-cured silicone-modified polyurethane resin through a two-step spraying method. Subsequently, these materials solidified together to successfully prepare a superhydrophobic coating with 159° contact angle and 2° sliding angle. The prepared silica/silicone-modified polyurethane (SiO2/SiPU) superhydrophobic coating showed superhydrophobic property after being cyclically rubbed for 30 cycles on 1000-mesh sandpaper under a load of 200 g. The coating further exhibited good corrosion resistance when placed in strong acid and alkali environments and excellent self-cleaning properties in air. This simple and environmentally friendly approach may have enormous application potential in many fields.
A general partial wetting model to describe an intermediate wetting state is proposed in this study to explain the deviations between the experimental results and classical theoretical wetting models for hydrophobic surfaces. We derived the theoretical partial wetting model for the static intermediate wetting state based on the thermodynamic energy minimization method. The contact angle based on the partial wetting model is a function of structural parameters and effective wetting ratio f, which agrees with the classical Wenzel and Cassie–Baxter models at f=1 and 0, respectively. Si samples including porous surfaces, patterned surfaces and hierarchical nano/microstructured surfaces were prepared experimentally, having same chemical composition but different physical morphology. We found that the experimental water contact angles deviate significantly from the classical Wenzel and Cassie–Baxter models but show good agreement with the proposed partial wetting model.
Nanostructured materials have shown extraordinary promise for high surface area applications. Here we report the design of polystyrene (PS)‐silicone nanofilaments (SNFs) composites, which can be flexibly grown on various substrates. The high surface area achieved by the SNFs is further extended by grafting with polystyrene. By changing the polymerization conditions and post treatment methods, the morphology of grafted PS is easily tuned into three types: leaf‐shaped, bead‐shaped and well‐wrapped. The tuneable morphology of PS is optimized for oil‐water separation and photocatalytic reactions and exhibited improved performances.
Additive Manufacturing (AM) has the potential to facilitate the limitless design and fast fabrication of silicone structures with controllable internal features and heterogeneous properties. The challenging task of developing AM systems able to handle viscous thermosetting silicones is reviewed in this work, with a focus on their use for biomedical applications. Moreover, the development of silicone tailored for AM is reviewed by examining three areas of curing mechanisms, rheological properties, and mechanical performance.
Additive manufacturing (AM) or 3D printing has revolutionized the manufacturing world through its rapid and geometrically-intricate capabilities as well as economic benefits. Countless businesses in automotive, aerospace, medical, and even food industries have adopted this approach over the past decade. Though this revolution has sparked widespread innovation with single material usage, the manufacturing world is constantly evolving. 3D printers now have the capability to create multi-material systems with performance improvements in user-definable locations. This means throughout a single component, properties like hardness, corrosion resistance, and environmental adaptation can be defined in areas that require it the most. These new processes allow for exciting multifunctional parts to be built that were never possible through traditional, single material AM processes. AM of metals, ceramics, and polymers is currently being evaluated to combine multiple materials in one operation and has already produced never-before-produced parts. While multi-material AM is still in its infancy, researchers are shifting their mindset toward this unique approach showing that the technology is beginning to advance past a research and development stage into real-world applications. This review is intended to highlight the range of 3D printed polymer-based, metal-metal, and metal-ceramic applications while discussing advantages and challenges with additively manufactured multi-material structures.
The current lifestyles, increasing population and limited resources result in energy research being at the forefront of worldwide grand challenges, increasing the demand for sustainable and more efficient energy devices. In this context, Additive Manufacturing brings the possibility of making electrodes and electrical energy storage (EES) devices in any desired 3D shape and dimensions, while preserving the multifunctional properties of the active materials in terms of surface area and conductivity. This paves the way to optimized and more efficient designs for energy devices. Here we describe how three-dimensional (3D) printing will allow the fabrication of bespoke devices - with complex geometries, tailored to fit specific requirements and applications - by designing water-based thermo-responsive inks to 3D-print different materials in one step. For example, printing the active material precursor (Chemically Modified Graphene, rCMG) and the current collector (copper) for supercapacitors or anodes for Lithium-ion batteries (LIBs). The formulation of thermo responsive inks using Pluronic F127 provides an aqueous-based, robust, flexible and easy scalable-up approach. The devices are designed to provide low resistance interface, enhanced electrical properties, mechanical performance, packing of rCMG and low active material density while facilitating the post-processing of the multicomponent 3D printed structures. The electrode materials are selected to match post-processing conditions. The reduction of the active material (rCMG) and sintering of the current collector (Cu) take place simultaneously. The electrochemical performance of the rCMG-based self-standing binder-free electrode and the two-materials rCMG/Cu printed prove the potential of multi-material printing in energy applications.
Sessile droplets are non-movable droplets spanning volumes in the nL-to-µL range. The sessile-droplet-based platform provides a paradigm shift from the conventional, flow-based lab-on-a-chip philosophy, yet offering similar benefits: low reagent/sample consumption, high throughput, automation, and most importantly flexibility and versatility. Moreover, the platform relies less heavily on sophisticated fabrication techniques, often sufficient with a hydrophobic substrate, and no pump is required for operation. In addition, exploiting the physical phenomena that naturally arise when a droplet evaporates, such as the coffee-ring effect or Marangoni flow, can lead to fascinating applications. In this review, we introduce the physics of droplets, and then focus on the different types of chemical and biological assays that have been implemented in sessile droplets, including analyte concentration, particle separation and sorting, cell-based assays, and nucleic acid amplification. Finally, we provide our perspectives on this unique micro-scale platform.
Superhydrophobic surface simultaneously possessing exceptional stretchability, robustness, and non-fluorination is highly desirable in applications ranging from wearable devices to artificial skins. While conventional superhydrophobic surfaces typically feature stretchability, robustness, or non-fluorination individually, co-existence of all these features still remains a great challenge. Here we report a multi-performance superhydrophobic surface achieved through incorporating hydrophilic micro-sized particles with pre-stretched silicone elastomer. The commercial silicone elastomer (Ecoflex) endowed the resulting surface with high stretchability; the densely packed micro-sized particles in multi-layers contributed to the preservation of the large surface roughness even under large strains; and the physical encapsulation of the microparticles by silicone elastomer due to the capillary dragging effect and the chemical interaction between the hydrophilic silica and the elastomer gave rise to the robust and non-fluorinated superhydrophobicity. It was demonstrated that the as-prepared fluorine-free surface could preserve the superhydrophobicity under repeated stretching-relaxing cycles. Most importantly, the surface’s superhydrophobicity can be well maintained after severe rubbing process, indicating wear-resistance. Our novel superhydrophobic surface integrating multiple key properties, i.e. stretchability, robustness, and non-fluorination, is expected to provide unique advantages for a wide range of applications in biomedicine, energy, and electronics.
Chemical composition and shape determine the basic properties of any object. Commonly, chemical synthesis and shaping follow each other in a sequence, although their combination into a single process would be an elegant simplification. Here, a pathway of simultaneous synthesis and shaping as applied to polysiloxanes on the micro- and nanoscale is presented. Complex structures such as stars, chalices, helices, volcanoes, rods, or combinations thereof are obtained. Varying the shape-controlling reaction parameters including temperature, water saturation, and the type of substrate allows to direct the reaction toward specific structures. A general mechanism of growth is suggested and analytical evidence and thermodynamic calculations to support it are provided. An aqueous droplet in either gaseous atmosphere or in a liquid organic solvent serves as a spatially confined polymerization volume. By substituting the starting materials, germanium-based nanostructures are also obtained. This transferability marks this approach as a major step toward a generally applicable method of chemical synthesis including in situ shaping.
Although known for more than 40 years in the polymer chemistry field, the photochemical radical thiol–ene addition (PRTEA) has been recently recognized as a chemical reaction with click characteristics. Photoinitiation enables spatial and temporal control of this highly efficient reaction, bridging simple organic chemistry with high-end materials synthesis and surfaces functionalization. In this minireview, we focus on the latest contributions based on the PRTEA for the synthesis of chemical precursors for silica and transition metal oxides (TMO) based materials. We summarize the mechanism of the PRTEA, the development of new families of photoinitiators and how this extremely simple approach has spilled over into the materials science arena with clear success. In particular, PRTEA adds to the collective efforts for building a reliable and straightforward chemical toolbox for surface modification and the production of sol–gel precursors, nanoparticles and thin films. The excellent perspectives for simple molecular and supramolecular building block synthesis opens up a rational synthetic route for the design and integration of these components in multipurpose platforms.
Omniphobic surfaces are created by designing an array of overhanging microdisks on a polymer film through two steps of photolithography. Two distinct edges and the large height of the microdisks relative to their separation ensure the formation of an air mat under the microdisks, providing an omniphobic property. Moreover, the freestanding omniphobic films are transparent and flexible, potentially serving as liquid-repellent surfaces in various applications.
Reactive superhydrophobic surfaces are highly promising for biotechnological, analytical, sensor or diagnostic applications but are difficult to realize due to the chemical inertness of most superhydrophobic surfaces. In this communication, we report on a photoactive, inscribable, non-wettable and transparent surface (PAINTS), prepared by polycondensation of trichlorovinylsilane to form thin transparent reactive porous nanofilament on a solid substrate. The PAINTS shows excellent superhydrophobicity and can be conveniently functionalized with the photo click thiol-ene reaction. In addition, we show for the first time that the PAINTS bearing vinyl groups can be easily modified with disulfides under UV irradiation. The effect of superhydrophobicity of PAINTS on the formation of high-resolution surface patterns has been investigated. The developed reactive superhydrophobic coating can find applications for surface bio-functionalization using abundant disulfide bearing biomolecules, such as peptides, proteins, or antibodies.
Nepenthes pitcher inspired anti-wetting coatings, fluoro-SNs/Krytox, are successfully fabricated by the combination of fluoro-silicone nanofilaments (fluoro-SNs) and Krytox liquids, perfluoropolyethers. Fluoro-SNs with different microstructure are grown onto glass slides using trichloromethylsilane by simply repeating the coating step, and then modified with 1H,1H,2H,2H-perfluorodecyltrichlorosilane. Subsequently, the Krytox liquid is spread on the fluoro-SNs coatings via capillary effect. The fluoro-SNs/Krytox coatings feature ultra-low sliding angle for various liquids, excellent stability, and transparency. The sliding speed of liquid drops on the fluoro-SNs/Krytox coating is obviously slower than on the lotus inspired superhydrophobic and superoleophobic coatings, and is controlled by composition of the coating (e.g., morphology of the fluoro-SNs, type of Krytox and its thickness) and properties of the liquid drops (e.g., density and surface tension). In addition, the self-cleaning property of the fluoro-SNs/Krytox coating is closely related to properties of liquid drops and dirt.
A decade ago one-dimensional silicone nanofilaments (1D-SNF) such as fibres and wires were described for the first time. Since then, the exploration of 1D-SNF has led to remarkable advancements with respect to material science and surface science: one-, two- and three-dimensional nanostructures of silicone were unknown before. The discovery of silicone nanostructures marks a turning point in the research on the silicone material at the nanoscale. Coatings made of 1D-SNF are among the most superhydrophobic surfaces known today. They are free of fluorine, can be applied to a large range of technologically important materials and their properties can be modified chemically. This opens the way to many interesting applications such as water harvesting, superoleophobicity, separation of oil and water, patterned wettability and storage and manipulation of data on a surface. Because of their high surface area, coatings consisting of 1D-SNF are used for protein adsorption experiments and as carrier systems for catalytically active nanoparticles. This paper reviews the current knowledge relating to the broad development of 1D-SNF technologies. Common preparation and coating techniques are presented along with a comparison and discussion of the published coating parameters to provide an insight on how these affect the topography of the 1D-SNF or coating. The proposed mechanisms of growth are presented, and their potentials and shortcomings are discussed. We introduce all explored applications and finally identify future prospects and potentials of 1D-SNF with respect to applications in material science and surface science.
In the present work, we have successfully fabricated a polyelectrolyte tethered transparent surface, on which superhydrophobicity and superhydrophilicity can be reversibly switched via counterion exchange between chloride ion (Cl-) and perfluorooctanate ion (PFO-). The stable superhydrophobic state can be obtained only when a certain extent of fluorine is chemically incorporated into the grafted polyelectrolyte. The counterion exchange does not have any influence on the transmittance of the transparent surface. The superhydrophobicity and superhydrophilicity can be reversibly switched on the surface for many cycles without any apparent damage to the wetting properties. Additionally, the transparent surface can be applied to prepare smart glass displays to hide and convey information by patterning the counterion distribution on the surface based on the different antifogging properties between superphydrophobic and superhydrophilic surfaces.
Two kinds of novel POSS cross-linkers were firstly prepared via hydrosilylation of Vinyl-POSS and trimethoxysilane. And two types of novel polydimethylsiloxane (PDMS) polymer composites as RTV silicone rubbers were prepared using Vinyl-POSS derivatives as cross-linkers in the presence of organotin catalyst. To completely exhibit superiorities of two kinds of novel cross-linkers, RTV silicone rubbers prepared with two proportions of different cross-linkers were assessed. The chemical inclusion of novel POSS into PDMS networks by hydrolytic condensation reaction was verified by attenuated total reflection (ATR) infrared spectroscopy. Morphologies, thermal properties, mechanical properties and hardness of these novel RTV silicone rubbers were studied. The results exhibited significantly enhanced effects of POSS on thermal stabilities, mechanical properties and hardness as compared to the PDMS polymers prepared with the traditional tetra-functional TMOS and TEOS cross-linkers. The striking improvements in thermal properties, mechanical properties and hardness could be attributed to the synergistic effect of the increase of dimensionality of cross-linked networks in novel RTV silicone rubbers resulting from special three-dimensional structure of novel POSS cross-linkers, plasticization of self-cross-linked POSS cross-linkers and uniform distribution of POSS cross-linkers.
A multi-material stereolithography (MMSL) machine was developed by retrofitting components from a commercial 3D Systems 250/50 stereolithography (SL) machine on a separate stand-alone system and adapting the components to function with additional components required for MMSL operation. The MMSL machine required construction of a new frame and the development of a new rotating vat carousel system, platform assembly, and automatic leveling system. The overall operation of the MMSL system was managed using a custom LabVIEW® program, which included controlling a new vat leveling system and new linear and rotational stages, while the commercial SL control software (3D Systems Buildstation 4.0) was retained for controlling the laser scanning process. During MMSL construction, the sweeping process can be inhibited by previously cured layers, and thus, a deep-dip coating process without sweeping was used with low viscosity resins. Low viscosity resins were created by diluting commercial resins, including DSM Somos® WaterShed™ 11120, ProtoTherm™ 12120, and 14120 White, with propoxylated (2) neopentyl glycol diacrylate (PNGD). Several multi-material complex parts were produced providing compelling evidence that MMSL can produce unique parts that are functional, visually illustrative, and constructed with multi-materials.
The surface of silicone rubber swelled and was modified by 157-nm F2 laser irradiation at a laser fluence less than the ablation threshold. The irradiated surface swelled to a height of approximately 3m. Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy showed that the irradiated surface was modified to SiO2. 193-nm ArF laser irradiation of the silicone rubber induced the surface to swell, but not to modify to SiO2. The IR peaks of end groups of silicone were observed in the FT-IR spectra of the surface. From these results, it is concluded that the main chains (Si-O) of silicone were photodissociated and generation of low molecular weight silicones caused the swelling. In addition, it was observed that methane and carbon dioxide were released from silicone rubber when each laser beam irradiated it. These gases were generated by photodissociation of the side chains (Si-CH3) of silicone. An F2 laser beam can photodissociate the Si-CH3 bonds and the Si-O bonds of silicone and O2 effectively even at a laser fluence less than the ablation threshold, resulting in the modification to SiO2 and the swelling.
A superhydrophobic fabric coating made of a crosslinked polydimethylsiloxane elastomer, containing well-dispersed hydrophobic silica nanoparticles and fluorinated alkyl silane, shows remarkable durability against repeated machine washes, severe abrasion, strong acid or base, boiling water or beverages and excellent stain resistance.
The effect of surface modification with 3-aminopropyltriethoxysilane (APTES) and n-propyltriethoxysilane (PTES) on photo-catalytic activity and UV-shielding ability of fine TiO2 particles were investigated. The number of surface groups (NR) [nm−2] which shows the density of modifier on TiO2 surface was calculated from the results of elemental analysis and BET measurement. The modified samples of which NR are different were obtained by changing the concentration of modifier. When the photo-catalytic activity and UV-shielding ability of modified samples were evaluated, it was found that APTES was more effective modifier than PTES to obtained samples with low photo-catalytic activity and high UV-shielding ability. This is probably because the adsorption mechanisms on TiO2 surface between modifiers were different and NR is a key factor to control the performances of fine TiO2 particles. The result of zeta potential showed that surface character of modified samples was varied by changing NR. It suggested from these results that NR affected the photo-catalytic activity and UV-shielding ability because NR changed surface character of modified samples.
Functionalized trialkoxysilanes are widely used to modify the surface properties of materials and devices. It will be shown that the photoinitiated radical-based thiol-ene "click" reaction provides a simple and efficient route to diverse trialkoxysilanes. A total of 15 trialkoxysilanes were synthesized by reacting either alkenes with 3-mercaptopropyltrialkoxysilane or thiols with allyltrialkoxysilanes in the presence of a photoinitiator. The functionalized trialkoxysilanes were obtained in quantitative to near-quantitative yields with high purity. The photochemical reactions can be run neat in standard borosilicate glassware using a low power 15-W blacklight. A wide range of functional groups is tolerated in this approach, and even complex alkenes click with the silane precursors. To demonstrate that these silanes can be used as surface coating agents, several were reacted with iron oxide superparamagnetic nanoparticles and the loadings quantified. The photoinitiated thiol-ene reaction thus offers a facile and efficient method for preparing surface-active functional trialkoxysilanes.
A micropatterned superhydrophobic/superhydrophilic surface was successfully fabricated by plasma CVD and VUV irradiation. Physicochemical properties of the superhydrophobic, superhydrophilic, and superhydrophobic/superhydrophilic surfaces were investigated. The roughness structures on the superhydrophilic surface remained intact compared to those of the superhydrophobic surface. The micropatterned superhydrophobic/superhydrophilic surface was used as a scaffold of cell culture. On the micropatterned surface, the cells attached to the superhydrophilic regions in a highly selective manner, forming circular microarrays of the cells corresponding to the pattern. On the micropatterned surface with pattern distances of 200 microm between superhydrophilic regions, the cells adhered on the superhydrophilic regions and partly extended to the neighboring cells. In contrast, when the pattern distances between the superhydrophilic regions were more than 400 microm, the cells did not extend to the neighboring cells. Cell adhesion behaviors on superhydrophobic and superhydrophilic surfaces were also examined. The cells adhered and proliferated on both superhydrophobic and superhydrophilic surfaces. However, on the superhydrophobic surface, constant contact to facilitate cell division and proliferation was required. On the other hand, the cells easily adhered and proliferated on the superhydrophilic surface immediately after seeding. These differences in cell adhesion behavior induced site-selective cell adhesion on the superhydrophilic regions. Furthermore, protein adsorption behavior that plays an important role in cell adhesion on flat hydrophobic and hydrophilic surface was also examined. The amounts of the protein adsorption on the flat hydrophilic surface were much greater than those on the flat hydrophobic surface.
A strategy to create a superhydrophobic surface by employing microlens and microbowl arrays without a thin fluorinated carbon film coating was described. The wettability and switching of adhesive force was checked by fabricating PDMS microbowl arrays with imprinted inverse microlens structure following the lock-and-key domains. No distortion is observed on the array surface, suggesting that this approach eliminates significant drawbacks encountered with conventional bottom-up techniques. The variation of the contact angles measured at different sites imply that the PDMS microlens-arrayed surface has hydrophobity with a high adhesive force. The results also show that the 10×6 PDMS microbowl-arrayed surface exhibits perfect superhydrophobicity with a contact angle of approximately 164.6°, owing to the hollow structures in the surface.