Surface structuration (micro and/or nano) governed by the fluorinated tail lengths toward superoleophobic surfaces

As compared to superhydrophobic surfaces, the challenge to obtain superoleophobic properties, surfaces against low-surface-tension probe liquids such as hexadecane, is very important because of their high tendency to wet. From the molecular design of the monomer, it is possible to obtain in one step superoleophobic surfaces by electrodeposition. Hence, we report the synthesis and the characterization of an original series of fluorinated 3,4-ethylenedioxypyrrole (EDOP) derivatives. The electrodeposited polymer films are characterized by contact angle measurements (static and dynamic with various probe liquids), optical profilometry, and scanning electron microscopy. In the view toward reaching superoleophobic properties, a common approach is to increase the number of fluoromethylene units of the surface post-treatment agent. Here, surprisingly, it is possible, in one step, to reach more efficient antioil surface properties by decreasing the length of the fluorinated tail (F-octyl to F-hexyl). This fact can be explained by a double scale of structuration (micro and nano) induced using only F-hexyl tails.     

Self-assembly of amino-functionalized monolayers on silicon surfaces and preparation of superhydrophobic surfaces based on alkanoic acid dual layers and surface roughening

Reproducibly smooth amino-functionalized surfaces were obtained by deposition of aminopropyltrimethoxysilane (APTMS) at the vapor/solid interface. Characteristics of these amino-functionalized surfaces were evaluated based on atomic force microscopy, water contact angle measurement and X-ray photoelectron spectroscopy. The results showed that APTMS modified surfaces are very homogeneous and the chemical reactivity of modified surfaces can be ensured with high free amino content. Furthermore, for the purpose of tailoring the wettability of silicon surface, dual self-assembled films were achieved by performing reaction between amino-functionalized surface and n-alkanoic acids with different chain length. The wettability of the self-assembled films can be adjusted with altering the hydrocarbon chain length of alkanoic acids. Moreover, cooperation of dual self-assembled films with surface roughening, superhydrophobic surfaces with CA larger than 153 degrees were obtained. Thus, the wettability of modified surfaces can be altered greatly with changing hydrocarbon chain length of self-assembled films.     

Hydrocarbon versus fluorocarbon in the electrodeposition of superhydrophobic polymer films

To elaborate on superhydrophobic surfaces, we report the electrochemical synthesis, surface morphology, and wettability of hydrocarbon conductive polymer films obtained by the electrodeposition of polythiophene, poly(3,4-ethylenedioxythiophene) (i.e., PEDOT), and poly(3,4-ethylenedioxypyrrole) (i.e., PEDOP) derivatives. Highly hydrophobic films were obtained from n-C(14)H(29) and n-C(8)H(17) chains in the cases of polythiophenes and PEDOP, respectively. By contrast, superhydrophobic films were formed by the deposition of PEDOT substituted with n-C(10)H(21) chains (PEDOT-methyl undecanoate): static contact angle ≈ 160.6°, hysteresis ≈ 2°, and sliding angle ≈ 3°. Their surface properties were compared to those of previously reported fluorinated analogues. The water-repellent properties of PEDOT-methyl undecanoate were similar to the best surface properties obtained with fluorinated monomers. Even if the main approach for the chemical factor to build up superhydrophobic surfaces is via a coating of a fluorinated compound, this work confirms that the formation of fractal surfaces is able to achieve super-anti-wetting properties within a hydrocarbon series (less expensive with a favorable ecotoxic approach), and it opens a new path to bioinspired surfaces.     

Superhydrophobic and lipophobic properties of self-organized honeycomb and pincushion structures

This report describes the simple preparation of superhydrophobic and lipophobic surfaces by self-organization. Microporous polymer films of a fluorinated polymer with hexagonally arranged pores were prepared by casting from solution under humid conditions. Hexagonally packed water microdroplets were formed by evaporative cooling on the surface of the casting solution. After solvent evaporation, a honeycomb-patterned polymer film was formed with the water droplet array acting as a template; the water droplets themselves evaporated soon after the solvent. Two porous polymer layers were stacked vertically, separated by pillars at the hexagon vertexes. After peeling off the top layer using adhesive tape, a pincushion-like structure was obtained. Here, we show that superhydrophobic behavior was achieved, with the maximum contact angle, 170 degrees, observed using these pincushion structures. Theoretical calculations fit the experimental results well. The lipophobic properties of the films are also discussed.     

Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer

The pulsed plasma polymerization of low molecular weight molecules containing only one (ethylene oxide vinyl ether) and two (diethylene oxide vinyl ether) ethylene oxide units were investigated. The surface density of EO units retained in the polymer films increases sharply with decreasing average power input during deposition, particularly at very low plasma duty cycles. The protein adsorption properties of these plasma synthesized polymer were investigated using ¹²⁵I-labeled albumin and fibrinogen. Surprisingly effective, non-fouling surfaces were observed with films synthesized from the monomer containing two ethylene oxide units; however, the monomer containing only one EO unit gave surfaces that were not particularly effective in preventing protein adsorptions. The results obtained show that ultra short chain length PEO modified surfaces can be biologically non-fouling. This, in turn, has interesting consequences in terms of trying to identify the basic reason for the effectiveness of EO units in preventing biomolecule adsorptions on surfaces.     

Direct catalytic route to superhydrophobic polyethylene films

Polyethylene films grow on a flat silica surface modified by the bis(imino)pyridyl iron(II) catalyst during ethylene polymerization in toluene solvent. The resulting films show superhydrophobic properties. Advancing water contact angle as high as 169 degrees and sliding angles as low as 2 degrees are obtained on these films. SEM images reveal special surface structures of these films containing micrometer-sized islands, submicrometer particles on the islands, and stress nanofibers between the islands, which render superhydrophobicity to the polyethylene surfaces. After the submicrometer particles and stress nanofibers are removed by annealing, the superhydrophobic properties of the polymer films disappear.     

Fabrication and characterization of superhydrophobic silica nanotrees

Superhydrophobic silica nanotrees were obtained by sol–gel method with hybrid silica sol and jelly-like resorcinol formaldehyde resin. Rough surfaces were obtained by removing the organic polymer at high temperature. After the films with rough surface were modified by trimethylchlorosilane (TMCS), the wettability of the film changed from superhydrophilic to superhydrophobic. The surface roughness of the silica nanotrees film is about 20 nm, and it is transparent and superhydrophobic with a water contact angle higher than 150°.     

Fabricating superhydrophobic surfaces by molecular accumulation of polysiloxane on the wool textile finishing

In the present study, a novel and simple method of obtaining superhydrophobic surface through the migration of organic siloxane segments in the acrylate side chains to the outmost layer and forming the nano-protuberance on the micro-roughness wool fabrics was described. The chemical compositions and morphologies of the untreated/treated fabrics were characterized by the scanning electron microscopy and X-ray photoelectric energy spectroscopy. Meanwhile, the surface hydrophobicity was evaluated by the static contact angle measurement. The scanning electron microscopy photographs showed that the fiber surfaces of the treated fabrics were obviously granulated, and a wax film covered on the fibers could be observed. X-ray photoelectron spectroscopy analyses and static contact angle measurement further testified that the component of the wax was almost siloxane and that the surfaces of the treated fabrics had superhydrophobic property. The above results indicated that this method could be extended to prepare superhydrophobic surfaces by migrating the low-surface-energy matter and fabricating the nanoscale roughness on the micro-roughness material surfaces.     

Poly[bis(2,2,2-trifluoroethoxy)phosphazene] superhydrophobic nanofibers

Nanofibers of poly[bis(2,2,2-trifluoroethoxy)phosphazene] were produced by electrospinning from solutions in tetrahydrofuran, methylethyl ketone, and acetone. The fiber diameter varied from 80 nm to 1.4 microm by changes in the concentration of the polymer solution. The electrospun nonwoven mats showed enhanced surface hydrophobicity compared to spun cast films with up to a 55 degrees increase in water contact angle. The hydrophobicity varied with fiber diameter and surface morphology, with contact angles to water being in the range of 135 degrees -159 degrees. A low value of hysteresis (<4 degrees) was recorded for the superhydrophobic surfaces. The extremely high hydrophobicity of these mats is a combined result of a fluorinated surface and the inherent surface roughness of an electrospun mat.     

Biomimetic superhydrophobic and highly oleophobic cotton textiles

We report a biomimetic procedure to prepare superhydrophobic cotton textiles. By in situ introducing silica particles to cotton fibers to generate a dual-size surface roughness, followed by hydrophobization with polydimethylsiloxane (PDMS), normally hydrophilic cotton has been easily turned superhydrophobic, which exhibits a static water contact angle of 155 degrees for a 10 microL droplet. The roll-off angle of water droplets depends on the droplet volume, ranging from 7 degrees for a droplet of 50 microL to 20 degrees for a 7 microL droplet. When a perfluoroalkyl chain is introduced to the silica particle surface, the superhydrophobic textile also becomes highly oleophobic, as demonstrated by a static contact angle of 140 degrees and a roll-off angle of 24 degrees for a 15 microL sunflower oil droplet.     

Controlling the wettability of hierarchically structured thermoplastics

Surfaces play an important role in defining the properties of materials, controlling wetting, adsorption, or desorption of biomolecules, and sealing/bonding of different materials. We have combined microscale features with plasma-etched nanoscale roughness and chemical modification to tailor the wettability of the substrates. Cyclic olefin polymers and copolymers (COPs/COCs) were processed to make a range of surfaces with controlled superhydrophobic or -hydrophilic properties. The hydrophobic properties of the polymers were increased by the introduction of microstructures of varying geometry and spacing through hot embossing. The COC/COP substrates were functionalized by plasma activation in O(2), CF(4), and a mixture of both gases. The plasma etching introduces nanoscale roughness and also chemically modifies the surface, creating either highly hydrophilic or highly hydrophobic (contact angle >150°) surfaces depending on the gas mixture. The influence of geometry and chemistries was characterized by atomic force microscopy, contact angle measurements, and X-ray photoelectron spectroscopy. Measurements of the contact angle and contact angle hysteresis demonstrated long-term stability of the superhydrophobic/superhydrophilic characteristics (>6 months).     

pH-responsive copolymer films by surface-catalyzed growth

We have engineered a new class of pH-responsive polymer films on gold surfaces by first developing a controlled, surface-catalyzed polymerization to prepare a copolymer film consistent with poly(methylene-co-ethyl acetate) and subsequently hydrolyzing the ester side chains to varying extents to yield carboxylic acids (denoted as PM-CO2H). When pH is increased, the acid groups become deprotonated or charged, dramatically increasing their water solubility and greatly altering the film properties. The carboxylic acid content within the copolymer film can be adjusted by changing the monomer concentration ratio used in the polymerization process or the length of time for the hydrolysis. We have designed PM-CO2H films to consist predominately (>95%) of polymethylene (PM) so that the film is hydrophobic in the uncharged state and, thereby, exhibits an extremely large pH-induced response in barrier properties once ionized. The effect of polymer composition on pH response was investigated by electrochemical impedance spectroscopy (EIS), reflectance-absorption infrared spectroscopy (RAIRS), and contact angle measurements. At a 1%-4% molar acid content, the copolymer film exhibits a 5 orders of magnitude change in its resistance to ion transport over 2-3 pH units. The pH at which this response begins can be tailored from pH 5 to pH 10 by decreasing the acid content in the film from 4% to 1%.     

PNIPAM chain collapse depends on the molecular weight and grafting density

This study demonstrates that the thermally induced collapse of end-grafted poly(N-isopropylacrylamide) (PNIPAM) above the lower critical solution temperature (LCST) of 32 degrees C depends on the chain grafting density and molecular weight. The polymer was grafted from the surface of a self-assembled monolayer containing the initiator (BrC(CH3)2COO(CH2)11S)2, using surface-initiated atom transfer radical polymerization. Varying the reaction time and monomer concentration controlled the molecular weight, and diluting the initiator in the monolayer altered the grafting density. Surface force measurements of the polymer films showed that the chain collapse above the LCST decreases with decreasing grafting density and molecular weight. At T > LCST, the advancing water contact angle increases sharply on PNIPAM films of high molecular weight and grafting density, but the change is less pronounced with films of low-molecular-weight chains at lower densities. Below the LCST, the force-distance profiles exhibit nonideal polymer behavior and suggest that the brush architecture comprises dilute outer chains and much denser chains adjacent to the surface.     

CaCO_3颗粒模板法制备聚合物超亲水/超疏水表面

以碳酸钙(CaCO3)颗粒层为模板,运用简单的热压和酸蚀刻相结合的方法制备聚合物超亲水/超疏水表面.首先在玻璃基底上均匀铺撒一层CaCO3颗粒,以此作为模板,通过热压线性低密度聚乙烯(LLDPE)使CaCO3颗粒均匀镶嵌在聚合物表面,获得了超亲水性质;进一步经酸蚀得到了具有微米和亚微米多孔结构的表面,其水滴静态接触角(WCA)可达(152.7±0.8)°,滚动角小于3°,具备超疏水性质.表面浸润性能和耐水压冲击性能研究表明该超疏水表面具有良好的稳定性和持久性.用同样工艺微模塑/酸蚀刻其它疏水性聚合物,得到类似结果.     

Large-area unmodified superhydrophobic copper substrate can be prepared by an electroless replacement deposition

Using an electroless replacement deposition method, large-area superhydrophobic metal substrate could be obtained. The superhydrophobic surfaces were prepared via a replacement reaction between copper substrate and HAuCl(4) solution. The roughness of the copper substrate increased much after the replacement reaction. X-ray powder diffraction (XRD) pattern and energy dispersive X-ray (EDX) spectroscopy have proved that gold, CuCl and Cu(2)O formed on the surface of copper substrate after the replacement reaction. The surface showed remarkable superhydrophobic properties with a contact angle higher than 150 degrees without any modification with a self-assembled monolayer (SAM) of long chain thiol or perfluoro molecules.     

Simulation of Sessile Water-Droplet Evaporation on Superhydrophobic Polymer Surfaces

Evaporation of sessile water-droplets on superhydrophobic polymer surfaces has been simulated in recent research. Models based on the ellipsoidal cap geometry and spherical cap geometry, which were originally put forward to describe the profile of a droplet during its evaporation process on a solid surface with a contact angle <90±, are developed to reveal the issue with an initial contact angles larger than 150±. To verify the validity of the model, experiments on superhydrophobic polycarbonate, and °uorinated polyurethane and poly (methyl methacrylate) blend surfaces were carried out. It was observed that the change trends of contact angle and height of the droplet against evaporation time on the superhydrophobic surfaces experimentally are consistent with the simulated results by ellipsoidal and spherical cap models. The ellipsoidal cap model shows the better fits due to the shape distortions of droplets.     

Superhydrophilic and superhydrophobic nanostructured surfaces via plasma treatment

Polyethylene terephthalate (PET) films have been structured with isolated nanofibrils and fibril bundles using oxidative plasma treatments with increasing etching ratios. The transition from fibrils to bundles was smooth and it was associated with a significant reduction in the overall top area fraction and with the development of a second organisation level at a larger length scale. This increased complexity was reflected in the surface properties. The surfaces with two-level substructures showed superhydrophilic and superhydrophobic properties depending on the surface chemistry. These properties were preserved during prolonged storage and resisted moderate mechanical stress. By combining different contact angle and drop impact measurements, the optimum surface design and plasma processing parameters for maximizing stability of the superhydrophobic or superhydrophilic properties of the PET films were identified.     

Influence of n-hexanol and n-octanol on wetting properties and air entrapment at superhydrophobic surfaces

Superhydrophobic surfaces have recently attracted a lot of attention due to their self-cleaning properties. The superhydrophobic surfaces used in our studies were prepared using a mixed inorganic-organic coating. In order to check how short chain surface active agents affect the surface energy of such surfaces, their wettability (sessile drop technique) and the kinetics of the three phase contact formation were studied. It was found that with increasing concentrations of n-hexanol and n-octanol the surface energy of these surfaces was only slightly changed, i.e. a small decrease in contact angle values with increasing solution concentration was detected. Even for the most concentrated n-hexanol and n-octanol solutions, the contact angles were in the range 145-155° and the drop rolled off, indicating that the studied surfaces stayed superhydrophobic. Air bubbles, upon collision with such superhydrophobic surfaces, spread over the superhydrophobic surface within milliseconds in the studied solutions.     

Fabrication of superhydrophobic surfaces by self-assembly and their water-adhesion properties

The self-assembled films of methyloctyldimethoxysilane (MODMS) and fluorooctylmethyldimethoxysilane (FODMS) were prepared on silicon surfaces and evaluated with AFM, water contact angle measurement, and X-ray photoelectron spectroscopy. Superhydrophobic surfaces were obtained by cooperation of MODMS and FODMS self-assembly with surface roughening. The results showed that preparing closely packed self-assembled films and fabricating surface nanometer-scale and micrometer-scale binary roughness can achieve superhydrophobic films with a water contact angle larger than 156 degrees. The difference between solution deposition and chemical vapor deposition is also investigated. Moreover, superhydrophobic surfaces created with MODMS and FODMS show the different water-adhesion effects, which could have great significance on liquid microtransport in microfluid devices.     

Reversible superhydrophobic to superhydrophilic conversion of Ag@TiO2 composite nanofiber surfaces

A new type of superhydrophobic material consisting of a surface with supported Ag@TiO(2) core-shell nanofibers has been prepared at low temperature by plasma-enhanced chemical vapor deposition (PECVD). The fibers are formed by an inner nanocrystalline silver thread which is covered by a TiO(2) overlayer. Water contact angles depend on the width of the fibers and on their surface concentration, reaching a maximum wetting angle close to 180 degrees for a surface concentration of approximately 15 fibers microm(-2) and a thickness of 200 nm. When irradiated with UV light, these surfaces become superhydrophilic (i.e., 0 degrees contact angle). The decrease rate of the contact angle depends on both the crystalline state of the titania and on the size of the individual TiO(2) domains covering the fibers. To the best of our knowledge, this is one of the few examples existing in the literature where a superhydrophobic surface transforms reversibly into a superhydrophilic one as an effect of light irradiation.