Wetting behavior of oleophobic polymer coatings synthesized from fluorosurfactant-macromers

Facile Fabrication of a Robust Superhydrophilic/Underwater Superoleophobic Material for Oil-Fouling Expulsion

The reduction of oil fouling in pipes and tanks is essential for the oil storage and transportation industry. In this study, a superhydrophilic/underwater superoleophobic surface (SUSS) with high wearability, weatherability, and durability was developed using a facile two-step synthesis method and used to expel fouled oil from the surface using water without a surfactant. Some typical oils, including kerosene and white oil, can be spontaneously expelled by static water; however, rapeseed oil requires motive water for expulsion because of its high affinity for the SUSS. Different occurrences can be estimated based on a correlated parameter, φ(Pe), which is calculated using an introduced dimensionless number, P e = σ L V u μ . A positive value of φ indicates the occurrence of fouled-oil expulsion by water replacement, whereas a negative value indicates no occurrence of this phenomenon. This study provides a facile strategy for the rapid cleansing of oil-fouled pipes and tanks without using a detergent, thereby lowering costs and environmental risks.

How to Make Plastic Surfaces Simultaneously Hydrophilic/Oleophobic?

Hydrophilic/oleophobic surfaces are desirable in many applications including self-cleaning, antifogging, oil-water separation, etc. However, making plastic surfaces hydrophilic/oleophobic is challenging due to the intrinsic hydrophobicity/oleophilicity of plastics. Here, we report a simple and effective method of making plastics hydrophilic/oleophobic. Plastics, including poly (methyl methacrylate) (PMMA), polystyrene (PS), and polycarbonate (PC), have been coated with a perfluoropolyether (PFPE) (i.e., commercially known as Zdol) via dip coating and then irradiated with UV/Ozone. The contact angle measurements indicate that the treated plastics have a lower water contact angle (WCA) and higher hexadecane contact angle (HCA), i.e., they are simultaneously hydrophilic/oleophobic. The Fourier transform infrared (FTIR) results suggest that UV/Ozone treatment introduces oxygen-containing polar groups on the plastic surfaces, which renders the plastic surfaces hydrophilic. Meanwhile, more orderly packed PFPE Zdol molecules, which is due to the UV-induced bonding between PFPE Zdol and the plastic surface, result in the oleophobicity. Moreover, the simultaneous hydrophilicity/oleophobicity of functionalized plastics does not degrade in aging tests, and they have superior antifogging performance and detergent-free cleaning capability. This simple method developed here potentially can be applied to other plastics and has important implications in the functionalization of plastic surfaces.

Janus Distillation Membrane via Mussel-Inspired Inkjet Printing Modification for Anti-Oil Fouling Membrane Distillation

In this work, inkjet printing technology was used to print a thin layer of a hydrophilic solution containing polydopamine as a binder and polyethyleneimine as a strong hydrophilic agent on a commercial hydrophobic membrane to produce a Janus membrane for membrane distillation. The pristine and modified membranes were tested in a direct-contact membrane distillation system with mineral oil-containing feedwater. The results revealed that an integrated and homogenous hydrophilic layer was printed on the membrane with small intrusions in the pores. The membrane, which contained three layers of inkjet-printed hydrophilic layers, showed a high underwater oil contact angle and a low in-air water contact angle. One-layer inkjet printing was not robust enough, but the triple-layer coated modified membrane maintained its anti-oil fouling performance even for a feed solution containing 70 g/L NaCl and 0.01 v/v% mineral oil concentration with a flux of around 20 L/m²h. This study implies the high potential of the inkjet printing technique as a facile surface modification strategy to improve membrane performance.

Polyimide based super-wettable membranes/materials for high performance oil/water mixture and emulsion separation: A review

This article reviews the application of highly heat and pressure resistant polyimide material for the development of membranes/materials that exhibit unique super-wettability, the characteristics pivotal for the efficient separation of oil-water mixture and emulsion. The polymerization of imide monomer in polyimide brings about the required porosity in the material, which in turn renders the crucial surface roughness, which is instrumental for establishing the desired super-wettability on the polyimide based membrane materials, in addition to the mechanical and thermal robustness. The membrane as the oil-water filtering medium can be either oil passing or water passing depends on the individual wettability of the membrane surface for oil and water, which in turn depend on the respective solid-liquid interfacial energy and the hierarchical surface roughness. Superhydrophobic/superoleophobic wetting characteristic of the surface repels water and allows oil to pass through the membrane medium, and the major disadvantage of this kind of oil/water separation is the rapid oil fouling of the membrane pores and the consequent less efficiency for oil water separation. On the other hand, the membrane surface engineered to have the Superhydrophilic/underwater superoleophobic wetting characteristics can be water passing, and the easy fouling of the membrane surface can be minimized. In the case of polyimide materials, there are lot of scopes to engineer the physical properties like surface energy and surface roughness of the membrane surface in order to obtain the required wettability. There have been many works focused on the application of different variants of polyimide materials for developing membrane for oil water separation. In this review, we present an itemized review of various works on polyimide materials based oil/water separation in terms of chemical, physical, structural and surface characteristics of the material.

Properties of some nonionic fluorocarbon surfactants and their mixtures with hydrocarbon ones

The adsorption of Zonyl FSN-100 (FSN100, having an average 14 oxyethylene units and 6 -CF₂ groups) and Zonyl FSO-100 (FSO100, having an average 10 oxyethylene units and 5 -CF₂ groups) as well as of their mixtures with p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10, 16 and 8 oxyethylene groups in molecule (TX100, TX165, TX114) and cetyltrimethylammonium bromide (CTAB) at the solution-air and polytetrafluoroethylene (PTFE)-solution and polymethyl methacrylate (PMMA)-solution interfaces as well as the composition of the surface mixed layer was discussed based on the literature data. The adsorption properties of nonionic fluorocarbon surfactants were compared to those of the classical ones on the basis of the Gibbs standard free energy of adsorption determined by different ways and the intermolecular interactions of the surfactant molecules through the water phase. The synergetic effect in the reduction of the water surface tension by the mixture of fluorocarbon and classical nonionic surfactant was shown and explained by the comparison of the composition of the mixed surface layer to those in the bulk phase. The composition of the mixed fluorocarbon and classical surfactant layer at the solution-air interface was compared to that formed at the PTFE-solution and PMMA-solution interfaces. The changes of the surface tension of the aqueous solution of the fluorocarbon surfactants and their mixtures with classical hydrocarbon ones and their adsorption were analyzed taking into account the PTFE and PMMA surface wettability. This analysis was also based on the components and parameters of the head and tail of the surfactants surface tension as well as those of PTFE and PMMA. Apart from adsorption and wetting properties the aggregation of the fluorocarbon surfactants and their mixtures was discussed. A specific attention was paid to the possibility of two CMC values in the case of nonionic fluorocarbon surfactants as well as the synergism in CMC of mixtures of nonionic fluorocarbon and hydrocarbon surfactants.

Applying an Oleophobic/Hydrophobic Fluorinated Polymer Monolayer Coating from Aqueous Solutions

Despite major advancements in the fabrication of low-surface-energy surfaces, the environmental consequences of their fabrication can be a serious issue, particularly in an industrial context. This is especially the case for fluorine-based coatings, which often require fluorinated solvents for their processing and applications. These solvents are not only detrimental to the ozone layer but also represent a potential workplace hazard because they tend to bioaccumulate. We describe the design, synthesis, and characterization of a new fluorinated-polymer coating that can be simply applied to surfaces from an aqueous environment using a dip-coating technique. This was made possible by copolymerizing three different methacrylate monomers, each serving a specific function. Namely, fluorinated methacrylate providing oleo/hydrophobicity, photocleavable polyethylene glycol (PEG) methacrylate promoting water solubility of the copolymer, and thioether-based methacrylate serving as an anchoring unit to a number of different substrates. This copolymer is initially grafted to the surface as a monolayer from an aqueous solvent, after which the system is treated with ultraviolet (UV) light, cleaving away the protecting PEG moieties to yield an oleo/hydrophobic surface.

Multifunctional membranes with super-wetting characteristics for oil-water separation and removal of hazardous environmental pollutants from water: A review

Over the past few years, oil-water separation techniques have been widely researched due to influences of oil pollution. The oil pollution is significantly increasing day-by-day because of ever-increasing usage of oil in daily routine of humans and industrial activities. The separation of water from oil-water emulsions/mixtures through membrane technology has provided absolute necessary qualities such as low cost, eco-friendly, easy-operation and energy efficient. To build up the filter membranes with special super-wettability properties and bearing excellent multifunctional applications is highly attractive research area in current decade. However, evolution of membrane technology suffered many deficiencies including severe fouling, short-standing against high flow speed, surface wettability disorders, non-reusable and limited application. In this review article, we outline the recent advances in membrane technology with respect to special super-wettability properties, enhanced characteristics for purpose to serve oil-water separation, and more specifically its multifunctional applications. Therefore, this study is made for membranes having other than applications, in addition to oil-water separation. Further, the wetting phenomenon of these multifunctional membranes is addressed and highlighted the brief overview of surface wetting types including Superhydrophobic-Superoleophilic membranes, Superhydrophilic-Superoleophobic membranes, and Superhydrophilic-underwater Superoleophobic membranes. Moreover, relative fabrication procedures and multifunctional applications of developed multifunctional super-wetting membranes are also discussed along with wetting behavior. Finally, the current developments and achievements for oil-water separation multifunctional super-wetting membranes are concluded. Besides, it also explores the future challenges and obstacles associated to these membranes. Hence, this article provides brief overview of advancement of oil-water separation based multifunctional super-wetting membranes and ended with new thoughts of further modification/enhancement.

A Review on Current Development of Membranes for Oil Removal from Wastewaters

The current situation with the problems associated with the removal of oil from wastewaters by membranes is being explored. Many types of membranes have been investigated—organic polymers, inorganic or ceramic species and hybrids of the two. Polymeric membranes can be designed to facilitate the passage of oil, but the more successful approach is with hydrophilic types that encourage the passage of water. Ceramic membranes have an advantage here as they are less often irreversibly fouled and give a higher recovery of oil, with a lower flux decline. Furthermore, they can be cleaned up by a simple heating procedure. More attention should be given to understanding the mechanism of fouling so that operating conditions can be optimised to further reduce fouling and further decrease the flux decline, as well as assisting in the design of antifouling membranes. Another obstacle to ceramic membrane use is the high cost of manufacture. Cheaper starting materials such as clays have been surveyed.

Creation of Superhydrophobic Coatings Based on MWCNTs Xerogel

The creation of hydrophobic anti-icing and self-cleaning coatings is a relevant task for many industrial sectors. The potential field of application includes production of liquid and gas separators and filters, the field of textiles and clothing, construction and new materials, optical and microelectronic devices, the field of automobile construction and maritime shipping as well as energy and agriculture. The article suggests a new approach to the creation of superhydrophobic anti-icing coatings, by drawing peeled multi-walled carbon nanotubes (MWCNTs) to the sample surface. This method allows you to combine the necessary factors: Low surface energy, micro-nano-roughness and hierarchical multi-scale. The authors investigated the dependence of the wetting angle of such a surface on the model of MWCNT, fractional composition and the polarity of the dissolvent. The suggested approach can be used to create superhydrophobic coatings with the additional function of removing static charge and heating the surface, which can be used in the field of energetics for protection against freezing of wind turbine blades and aircraft surfaces.

Separation Mechanism and Construction of Surfaces with Special Wettability for Oil/Water Separation

Oil leakage and the discharge of oil/water mixtures by domestic and industrial consumers have caused not only severe environmental pollution and a threat to all species in the ecosystem but also a huge waste of precious resources. Therefore, the separation of oil/water mixtures, especially stable emulsion, has become an urgent global issue. Recently, materials containing a special wettability feature for oil and water have drawn immense attention because of their potential applications for oil/water separation application. In this paper, we systematically summarize the fundamental theories, separation mechanism, design strategies, and recent developments in materials with special wettability for separating stratified and emulsified oil/water mixtures. The related wetting theories that unveil the physical underlying mechanism of the oil/water separation mechanism are proposed, and the practical design criteria for oil/water separation materials are provided. Guided by the fundamental design criteria, various porous materials with special wettability characteristics, including those which are superhydrophilic/underwater superoleophobic, superhydrophobic/superoleophilic, and superhydrophilic/in-air superoleophobic, are systemically analyzed. These superwetting materials are widely employed to separate oil/water mixtures: from stratified oil/water to emulsified ones. In addition, the materials that implement the demulsification of emulsified oil/water mixtures via the ingenious design of the multiscale surface morphology and construction of special wettability are also discussed. In each section, we introduce the design ideas, base materials, preparation methods, and representative works in detail. Finally, the conclusions and challenges for the oil/water separation research field are discussed in depth.

Water drop-surface interactions as the basis for the design of anti-fogging surfaces: Theory, practice, and applications trends

Glass- and polymer-based materials have become essential in the fabrication of a multitude of elements, including eyeglasses, automobile windshields, bathroom mirrors, greenhouses, and food packages, which unfortunately mist up under typical operating conditions. Far from being an innocuous phenomenon, the formation of minute water drops on the surface is detrimental to their optical properties (e.g., light-transmitting capability) and, in many cases, results in esthetical, hygienic, and safety concerns. In this context, it is therefore not surprising that research in the field of fog-resistant surfaces is gaining in popularity, particularly in recent years, in view of the growing number of studies focusing on this topic. This review addresses the most relevant advances released thus far on anti-fogging surfaces, with a particular focus on coating deposition, surface micro/nanostructuring, and surface functionalization. A brief explanation of how surfaces fog up and the main issues of interest linked to fogging phenomenon, including common problems, anti-fogging strategies, and wetting states are first presented. Anti-fogging mechanisms are then discussed in terms of the morphology of water drops, continuing with a description of the main fabrication techniques toward anti-fogging property. This review concludes with the current and the future perspectives on the utility of anti-fogging surfaces for several applications and some remaining challenges in this field.

Flourishing Bioinspired Antifogging Materials with Superwettability: Progresses and Challenges

Antifogging (AF) structure materials found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies, attracting enormous research interests owing to their potential applications in display devices, traffics, agricultural greenhouse, food packaging, solar products, and other fields. The outstanding performance of biological AF surfaces encourages the rapid development and wide application of new AF materials. In fact, AF properties are inextricably associated with their surface superwettability. Generally, the superwettability of AF materials depends on a combination of their surface geometrical structures and surface chemical compositions. To explore their general design principles, recent progresses in the investigation of bioinspired AF materials are summarized herein. Recent developments of the mechanism, fabrication, and applications of bioinspired AF materials with superwettability are also a focus. This includes information on constructing superwetting AF materials based on designing the topographical structure and regulating the surface chemical composition. Finally, the remaining challenges and promising breakthroughs in this field are also briefly discussed.

Tuning bandgap and surface wettability of NiFe2O4 driven by phase transition

Stress variation induced bandgap tuning and surface wettability switching of spinel nickel ferrite (NiFe2O4, NFO) films were demonstrated and directly driven by phase transition via a post-annealing process. Firstly, the as-deposited NFO films showed hydrophilic surface with water contact angle (CA) value of 80 ± 1°. After post-annealing with designed temperatures ranged from 400 to 700 °C in air ambience for 1 hour, we observed that the crystal structure was clearly improved from amorphous-like/ nanocrystalline to polycrystalline with increasing post-annealing temperature and this phenomenon is attributed to the improved crystallinity combined with relaxation of internal stress. Moreover, super-hydrophilic surface (CA = 14 ± 1°) was occurred due to the remarkable grain structure transition. The surface wettability could be adjusted from hydrophilicity to super-hydrophilicity by controlling grain morphology of NFO films. Simultaneously, the saturation magnetization (Ms) values of NFO films at room temperature increased up to 273 emu/cm3 accompanied with transitions of the phase and grain structure. We also observed an exceptionally tunable bandgap of NFO in the range between 1.78 and 2.72 eV under phase transition driving. Meanwhile, our work demonstrates that direct grain morphology combined with the stress tuning can strongly modulate the optical, surface and magnetic characteristics in multifunctional NFO films.

Fabricating Nanometer-Thick Simultaneously Oleophobic/Hydrophilic Polymer Coatings via a Photochemical Approach

The simultaneously oleophobic/hydrophilic coatings are highly desirable in antifogging, oil-water separation, and detergent-free cleaning. However, such coatings require special chemical structure, i.e., perfluorinated backbone and polar end-groups, and are too expensive for real-life application. Here, we have developed an UV-based photochemical approach to make nanometer-thick perfluoropolyethers without polar end-groups, which are not intrinsically simultaneously oleophobic/hydrophilic but cost-effective, become simultaneously oleophobic/hydrophilic. The contact angle, ellipsometry, and X-ray photoelectron spectroscopy (XPS) results indicated that the UV irradiation results in the covalent bonding between the polymer and the substrate, which renders more ordered packing of polymer chains and thus the appropriately small interchain distance. As a result, the small water molecules penetrate the polymer network while large oil molecules do not. As a result, the oil contact angle is larger than the water contact angle and the coating shows the simultaneous oleophobicity/hydrophilicity. Moreover, we also demonstrated that this nanometer-thick simultaneously oleophobic/hydrophilic coating has improved long-term antifogging performance and detergent-free cleaning capability and is mechanically robust. The photochemical approach established here potentially can be applied on many other polymers and greatly accelerate the development and application of simultaneously oleophobic/hydrophilic coatings.

Interfacial and Wetting Behavior of Cationic, Anionic and Nonionic Surfactants in the Absence and Presence of Lysozyme

Herein, we discuss various physicochemical properties of cationic (CTAB), anionic (SDBS) and nonionic (TX-100) surfactants in the presence and absence of lysozyme, at different temperatures by using tensiometery. The surface excess (Γmax) decreases with the increase in temperature for all three kinds of surfactants in the presence and absence of lysozyme, but the most prominent decrease is to be observed for SDBS as compared to CTAB and TX-100 in the presence of lysozyme. The minimum area per molecule (Amin) follows the opposite trend as expected. In addition, contact angle analysis was also done to observe the wettability of poly(methyl methacrylate) (PMMA) surface by these surfactants in the presence and absence of lysozyme.

Composite Membrane with Underwater-Oleophobic Surface for Anti-Oil-Fouling Membrane Distillation

In this study, we fabricated a composite membrane for membrane distillation (MD) by modifying a commercial hydrophobic polyvinylidene fluoride (PVDF) membrane with a nanocomposite coating comprising silica nanoparticles, chitosan hydrogel and fluoro-polymer. The composite membrane exhibits asymmetric wettability, with the modified surface being in-air hydrophilic and underwater oleophobic, and the unmodified surface remaining hydrophobic. By comparing the performance of the composite membrane and the pristine PVDF membrane in direct contact MD experiments using a saline emulsion with 1000 ppm crude oil (in water), we showed that the fabricated composite membrane was significantly more resistant to oil fouling compared to the pristine hydrophobic PVDF membrane. Force spectroscopy was conducted for the interaction between an oil droplet and the membrane surface using a force tensiometer. The difference between the composite membrane and the pristine PVDF membrane in their interaction with an oil droplet served to explain the difference in the fouling propensities between these two membranes observed in MD experiments. The results from this study suggest that underwater oleophobic coating can effectively mitigate oil fouling in MD operations, and that the fabricated composite membrane with asymmetric wettability can enable MD to desalinate hypersaline wastewater with high concentrations of hydrophobic contaminants.

A UV-driven superhydrophilic/superoleophobic polyelectrolyte multilayer film on fabric and its application in oil/water separation

A novel superhydrophilic/superoleophobic surface for oil/water separation was prepared through UV irradiation of a polyelectrolyte multilayer film with perfluorooctanoate as the counterions on a commercially available cotton fabric.

Mechanically durable, superoleophobic coatings prepared by layer-by-layer technique for anti-smudge and oil-water separation

Superoleophobic surfaces are of interest for anti-fouling, self-cleaning, anti-smudge, low-drag, anti-fog, and oil-water separation applications. Current bioinspired surfaces are of limited use due to a lack of mechanical durability. A so-called layer-by-layer approach, involving charged species with electrostatic interactions between layers, can provide the flexibility needed to improve adhesion to the substrate while providing a low surface tension coating at the air interface. In this work, a polyelectrolyte binder, SiO₂ nanoparticles, and a fluorosurfactant are spray deposited separately to create a durable, superoleophobic coating. Polydiallyldimethylammonium chloride (PDDA) polyelectrolyte was complexed with a fluorosurfactant layer (FL), which provides oil repellency while being hydrophilic. This oleophobic/superhydrophilic behavior was enhanced through the use of roughening with SiO₂ particles resulting in a superoleophobic coating with hexadecane contact angles exceeding 155° and tilt angles of less than 4°. The coating is also superhydrophilic, which is desirable for oil-water separation applications. The durability of these coatings was examined through the use of micro- and macrowear experiments. These coatings currently display characteristics of transparency. Fabrication of these coatings via the layer-by-layer technique results in superoleophobic surfaces displaying improved durability compared to existing work where either the durability or the oil-repellency is compromised.

Synthesis and Properties of Photoswitchable Carbohydrate Fluorosurfactants

We describe the parallel synthesis, photocontrollable surface tension, and antibacterial performance of a new class of carbohydrate fluorosurfactant. Novel fluorosurfactants comprised a mono- or disaccharide head group linked to an azobenzene unit that was variably substituted with a trifluoromethyl group. Fluorosurfactants were rapidly assembled using the venerable CuI-catalysed azide–alkyne cycloaddition reaction and exhibited light-addressable surface activity, excellent water solubility, and selective antibacterial activity against Gram-positive Staphylococcus aureus. Notably, the physicochemical and biological activity of these novel materials was heavily dependent on the nature of the head group and the position of the trifluoromethyl substituent on the azobenzene ring. The UV-adapted cis-isomer of fluorosurfactants displayed good thermal stability at ambient temperature, with little reversion to the stable trans isomer after 16 h. These novel, light-responsive materials should find broad interest in a range of biomedical and technological fields, including drug and gene delivery, self-cleaning oleophobic surfaces, and antibacterial coatings for medical devices.

Biomimetic super-lyophobic and super-lyophilic materials applied for oil/water separation: a new strategy beyond nature

Investigations in the field of oil/water separation materials with special wettability may accelerate the settlement of industrial oily wastewater and ocean oil spill accidents.

Fluoro- vs hydrocarbon surfactants: why do they differ in wetting performance?

Fluorosurfactants are the most effective compounds to lower the surface tension of aqueous solutions, but their wetting properties as related to low energy hydrocarbon solids are inferior to hydrocarbon trisiloxane surfactants, although the latter demonstrate higher surface tension in aqueous solutions. To explain this inconsistency available data on the adsorption of fluorosurfactants on liquid/vapour, solid/liquid and solid/vapour interfaces are discussed in comparison to those of hydrocarbon surfactants. The low free energy of adsorption of fluorosurfactants on hydrocarbon solid/water interface should be of a substantial importance for their wetting properties.

Separating oil-water nanoemulsions using flux-enhanced hierarchical membranes

Membranes that separate oil-water mixtures based on contrasting wetting properties have recently received significant attention. Separation of nanoemulsions, i.e. oil-water mixtures containing sub-micron droplets, still remains a key challenge. Tradeoffs between geometric constraints, high breakthrough pressure for selectivity, high flux, and mechanical durability make it challenging to design effective membranes. In this paper, we fabricate a hierarchical membrane by the phase inversion process that consists of a nanoporous separation skin layer supported by an integrated microporous layer. We demonstrate the separation of water-in-oil emulsions well below 1 μm in size. In addition, we tune the parameters of the hierarchical membrane fabrication to control the skin layer thickness and increase the total flux by a factor of four. These simple yet robust hierarchical membranes with engineered wetting characteristics show promise for large-scale, efficient separation systems.

Superhydrophilic and underwater superoleophobic poly(sulfobetaine methacrylate)-grafted glass fiber filters for oil-water separation

Oil-water separation is a major problem in industries such as oil production and wastewater treatment, where millions of gallons of oil-contaminated water are produced. Zwitterionic poly(sulfobetaine methacrylate) (pSBMA) is a superhydrophilic polymer due to its strong interaction with water via electrostatic interactions. By coating surfaces of filter media with such a superhydrophilic polymer, it is expected that one can effectively separate oil and water. In this work, pSBMA was grafted onto glass fiber surfaces using surface-initiated atom transfer radical polymerization (SI-ATRP). The in-air water contact angle of the pSBMA-treated glass was 8-15°, as compared to 31° for the control untreated glass, whereas the underwater-oil contact angle of the pSBMA-grafted glass was 162-169°, as compared to 142° for the control pristine glass, suggesting that the pSBMA-grafted glass slides are superhydrophilic and underwater superoleophobic. Such superhydrophilicity and underwater superoleophobicity were realized by modifying surface chemistry only, with no need to create rough surfaces. The pSBMA-grafted glass fiber filters demonstrated exceptional results at separating oil from water without even allowing miniscule amounts of visible oil to permeate through.

Elaboration of voltage and ion exchange stimuli-responsive conducting polymers with selective switchable liquid-repellency

In this work, we report the possibility to selectively switch by voltage and anion exchange the water-repellent properties, in comparison with the oil-repellent properties, of copolymers containing both fluorinated chain (EDOT-F8) and pyridinium (EDOT-Py(+)) moieties. Here, the fluorinated chains are necessary to reach superhydrophobic properties while the pyridinium moieties allow the switching in the wettability by counterion exchange. Because, conducting polymers can exist in their oxidized and reduced state, here, we report also the switching of their wettability by voltage. The best properties (superhydrophobic properties with low hysteresis and sliding and good oleophobic properties) are obtained for a % of EDOT-Py(+) of 25 %. Surprisingly, by reducing the polymer by changing the voltage, a selective decrease in the contact angle of water is observed, whereas that of oils (diiodomethane and hexadecane) remain unchanged, making it possible to have higher contact angles with diiodomethane than with water. Here, the switching in the wettability is due to the change of the water droplet from the Cassie-Baxter state to the Wenzel state by changing the voltage. Because of the presence of highly polar pyridinium groups and their perchlorate counterions, the wettability of oil droplets (diiodomethane and hexadecane) is not significantly affected. This effect is confirmed by changing the counterions with highly hydrophobic ones (C8F17SO3(-), Tf2N(-), or BF4(-)). Such materials are excellent candidates for oil/water separation membranes.

Ultrafast oleophobic-hydrophilic switching surfaces for antifogging, self-cleaning, and oil-water separation

Smooth copolymer-fluorosurfactant complex film surfaces are found to exhibit fast oleophobic-hydrophilic switching behavior. Equilibration of the high oil contact angle (hexadecane = 80°) and low water contact angle (<10°) values occurs within 10 s of droplet impact. These optically transparent surfaces display excellent antifogging and self-cleaning properties. The magnitude of oleophobic-hydrophilic switching can be further enhanced by the incorporation of surface roughness to an extent that it reaches a sufficiently high level (water contact angle <10° and hexadecane contact angle >110°), which, when combined with the inherent ultrafast switching speed, yields oil-water mixture separation efficiencies exceeding 98%.

Zwitter-wettability and antifogging coatings with frost-resisting capabilities

Antifogging coatings with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, under aggressive fogging conditions, these surfaces may exhibit frost formation or excess and nonuniform water condensation, which results in poor optical performance of the coating. In this paper, we show that a zwitter-wettable surface, a surface that has the ability to rapidly absorb molecular water from the environment while simultaneously appearing hydrophobic when probed with water droplets, can be prepared by using hydrogen-bonding-assisted layer-by-layer (LbL) assembly of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). An additional step of functionalizing the nano-blended PVA/PAA multilayer with poly(ethylene glycol methyl ether) (PEG) segments produced a significantly enhanced antifog and frost-resistant behavior. The addition of the PEG segments was needed to further increase the nonfreezing water capacity of the multilayer film. The desirable high-optical quality of these thin films arises from the nanoscale control of the macromolecular complexation process that is afforded by the LbL processing scheme. An experimental protocol that not only allows for the exploration of a variety of aggressive antifogging challenges but also enables quantitative analysis of the antifogging performance via real-time monitoring of transmission levels as well as image distortion is also described.

Superoleophobic surfaces through control of sprayed-on stochastic topography

The liquid repellency and surface topography characteristics of coatings comprising a sprayed-on mixture of fluoroalkyl-functional precipitated silica and a fluoropolymer binder were examined using contact and sliding angle analysis, electron microscopy, and image analysis for determination of fractal dimensionality. The coatings proved to be an especially useful class of liquid repellent materials due to their combination of simple and scalable deposition process, low surface energy, and the roughness characteristics of the aggregates. These characteristics interact in a unique way to prevent the buildup of binder in interstitial regions, preserving re-entrant curvature across multiple length scales, thereby enabling a wide range of liquid repellency, including superoleophobicity. In addition, rather than accumulating in the interstices, the binder becomes widely distributed across the surface of the aggregates, enabling a mechanism in which a simple shortage or excess of binder controls the extent of coating roughness at very small length scales, thereby controlling the extent of liquid repellence.