Mechanically durable biomimetic fibrous membrane with superhydrophobicity and superoleophilicity for aqueous oil separation

Developing an effective and mechanically durable biomimetic membrane for the separation of highly emulsified aqueous oil is significant but challenging owing to its low water flux and serious membrane fouling. In this work, a biomimetic membrane with superhydrophobicity and superoleophilicity was rationally developed via co-electrospinning of polysulfonamide/polyacrylonitrile (PSA/PAN) emulsion solution, followed by decorating of α-Fe₂O₃ nanowire onto the membrane surface to create membrane roughness, and grafting of 1H,1H,2H,2H-perfluorododecyltrichlorosilane (FTCS) to lower membrane surface free energy. Benefiting from the nanowire-wrapped rough membrane structure and the low surface free energy FTCS, the resultant membrane showed superhydrophobicity with a high water contact angle (WCA) of 156°, superoleophilicity with a low oil contact angle (OCA) of 0°, which can separate the highly emulsified aqueous oil with an ultrahigh permeation flux over 7000 L m⁻² h^-1 and high separation efficiency of about 99%. Significantly, the biomimetic membrane also displayed robust stability for long-term separation owing to its advantage of antifouling property, showing great potential applications in large-scale aqueous oil treatment.     

The superhydrophobicity of polymer surfaces: Recent developments

Superhydrophobicity is the extreme water repellence of highly textured surfaces. The field of superhydrophobicity research has reached a stage where huge numbers of candidate treatments have been proposed and jumps have been made in theoretically describing them. There now seems to be a move to more practical concerns and to considering the demands of individual applications instead of more general cases. With these developments, polymeric surfaces with their huge variety of properties have come to the fore and are fast becoming the material of choice for designing, developing, and producing superhydrophobic surfaces. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1203–1217, 2011     

Fabrication of CdS films with superhydrophobicity by the microwave assisted chemical bath deposition

A simple method of microwave assisted chemical bath deposition (MA-CBD) was adopted to fabricate cadmium sulfide (CdS) thin films. The superhydrophobic surface with a water contact angle (CA) of 151 degrees was obtained. Via a scanning electron microscopy (SEM) observation, the film was proved having a porous micro/nano-binary structure which can change the property of the surface and highly enhance the hydrophobicity of the film. A possible mechanism was suggested to describe the growth of the porous structure, in which the microwave heating takes an important role in the formation of two distinct characteristic dimensions of CdS precipitates, the growth of CdS sheets in micro-scale and sphere particles in nano-scale. The superhydrophobic films may provide novel platforms for photovoltaic, sensor, microfluidic and other device applications.     

Spontaneous wrinkling of layer-by-layer assembled polyelectrolyte films for humidity-responsive superhydrophobicity

The fabrication of smart films with reversible wettability enabled by the stimulus-induced morphology changes has attracted growing interest but remains a challenge. Here we report a smart film that can reversibly changes its wettability between transparent hydrophobicity to translucent superhydrophobicity through the humidity-induced wrinkling/de-wrinkling process. The film was fabricated by depositing hydrophobic SiO₂ nanoparticles (NPs) on poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) films, followed by partially exfoliating the films from the underlying substrates. The partially exfoliated PAA/PAH film can reversibly wrinkle and de-wrinkle when being alternately subjected to humid and dry environments. The deposition of hydrophobic SiO₂ NPs on the wrinkling PAA/PAH film does not hinder the humidity-enabled wrin-kling/de-wrinkling ability of the composite film. The hydrophobic SiO₂ NPs and the underlying humidity-wrinkling PAA/PAH film enable the composite film to spontaneously change from hydrophobic and transparent to superhydrophobic and translucent with the rise of environmental humidity.     

Exceptional superhydrophobicity and low velocity impact icephobicity of acetone-functionalized carbon nanotube films

We present a simple method to produce carbon nanotube-based films with exceptional superhydrophobicity and impact icephobicity by depositing acetone-treated single-walled carbon nanotubes on glass substrates. This method is scalable and can be adopted for any substrate, both flexible and rigid. These films have indicated a high contact angle, in the vicinity of 170°, proved both by static and dynamic analysis processes. The dynamic evaporation studies indicated that a droplet deposited on the treated films evaporated in the constant contact angle mode for more than 80% of the total evaporation time, which is definitely a characteristic of superhydrophobic surfaces. Furthermore, the acetone-functionalized films showed a strong ability to mitigate ice accretion from supercooled water droplets (-8 °C), when the droplets were found to bounce off the films tilted at 30°. The untreated nanotube films did not indicate similar behavior, and the supercooled water droplets remained attached to the films' surfaces. Such studies could be the foundation of highly versatile technologies for both water and ice mitigation.     

Electrochemical catalysis with redox polymer and polyion-protein films

Supramolecular redox-active assemblies on electrodes are of fundamental interest and can be used to create functioning devices such as sensors, biosensors, and bioreactors. The ability of redox-active films to mediate electron transfer reactions in 3-D dramatically increases the sensitivity with which target molecules can be determined. Metallopolyion hydrogel films immobilized on electrode surfaces exhibit many properties that are reminiscent of those shown by redox-active proteins. This review discusses the electrochemical properties and applications of such films, including mediating electron transfer between electrodes and oxidase enzymes. In addition, polyion-protein films grown layer by layer have certain advantages in device fabrication, including facilitating direct electron transfer for many proteins, mechanical stability, use of tiny amounts of protein, and control of film architecture. This review presents examples of iron heme proteins in films grown layer by layer by alternate electrostatic adsorption for catalytic reduction of hydrogen peroxide and trichloroacetic acid and for oxidation of styrene.     

Approach to excellent superhydrophobicity and corrosion resistance of carbon-based films by graphene and cobalt synergism

A new series of carbon-based films doped with graphene oxide and cobalt (G-Co/a-C:H films) were successfully prepared on Si substrate via one-step electrochemical deposition of methanol as the carbon source and graphene oxide/cobalt as the dopant. G-Co/a-C:H films were fabricated at various graphene oxide concentration for comparative experiments. It can be found that the graphene oxide and cobalt were well embedded in amorphous carbon matrix to form superhydrophobic G-Co/a-C:H film at the doping GO concentration of 0.007 mg/mL, which was confirmed by transmission electron microscopy (TEM). It was noted that the superhydrophobicity of the resulting surface derives from its rough surface with hierarchical micro-nanostructures and the presence of the low-surface-energy GO components on it. The hierarchical micro-nanostructures are attributed to the corporate joint of GO and cobalt to form the multilevel nanoscale composite interface. Specially, the as-fabricated superhydrophobic G-Co/a-C:H film could exhibit excellent self-cleaning ability and corrosion resistance, revealed by the self-cleaning and corrosion tests.     

Microscale golden Candock leaves self-aggregated on a polymer surface: Raman scattering enhancement and superhydrophobicity

Gold nanoparticles (AuNP's) prepared through a controllable synthesis and aggregation process are attractive for their unique properties that arise from their surface plasmon resonances (SPRs). However, aggregation-controlled AuNP's on amorphous surfaces have not been well explored. In this study, we present a simple in situ synthesis method for preparing AuNP's in which the AuNP's self-aggregate into microscale Candock-leaf-like structures on a polyelectrolyte film (PEF) surface. In this approach, the PEF plays an important role in adsorbing and storing AuCl(4)(-) as well as in controlling the release speed of AuCl(4)(-) in the preparation process. The mechanism for forming these Candock-leaf-like structures has been illustrated by both the growth process of gold nanoparticles and the Ostwald ripenning of the aggregations. AuNP's with a unique structure exhibited significantly enhanced surface Raman scattering and strong superhydrophobicity.     

Plasma-deposited metal-containing polymer films

The plasma treatment of vapors containing organometallic compounds (of Pd, Ni, Co, Sn, Au) and various alkenes has been used to prepare thin films, the composition and electrical resistivity of which could be varied over a wide range.     

Superconducting organic polymer films

A concept of producing superconducting composites by means of reticulate doping of polymers with low molecular weight organic superconductors is presented. The obtained polycarbonate films contain around 2 wt.% of BEDT-TTF polyiodides in a form of continuous crystalline network. D.c. and microwave conductivity measurements demonstrate, that the as-obtained reticulate composites show semiconducting-type properties. After annealing at optimized conditions a dramatic change occurs and the composites become metallic in the entire temperature range due to a conversion of various phases of the BEDT-TTF polyiodides into the metallic and superconducting β₁-phase. The composites show the superconducting transition below 5 K₁ as evidenced by magnetoresistance measurements, indicating that the content of the β₁-phase microcrystals in the conducting network exceeds the percolation threshold.     

Fabrication of highly antireflective silicon surfaces with superhydrophobicity

Highly antireflective porous silicon surfaces with superhydrophobicity were obtained by means of chemical etching and fluoroalkylsilane self-assembly. The results show that wettability and reflectivity of these surfaces strongly depend on the etching method and the resultant surface morphology. All of the four resultant porous silicon surfaces by alkaline etching, acidic etching, thick Pt-assisted acidic etching, and thin Pt-assisted acidic etching can reduce reflectance, but the efficiency differs greatly. Except for the alkaline etching, the porous silicon surfaces produced by the other three etching methods can reach superhydrophobicity after fluoroalkylsilane modification. These differences are due to the different surface morphology and roughness. Moreover, the porous silicon surface produced by thin Pt-assisted acidic etching presents abundant holes and particles with diameters ranging from nanometers to submicrometers. This morphology enables the porous silicon surface to own a very low reflectance value that is averaged to be about 3% over the whole experimental photon wavelength spanning 300-800 nm.     

Electrochemical sensing with electrodes modified with molecularly imprinted polymer films

This article summarises our work on the development of voltammetric sensors based on molecularly imprinted polymers. Several recognition elements and integration strategies were used:1.membranes electropolymerised at the electrode surface; 2.casting of polymeric membranes by drop-coating a solution of pre-formed polymer (polyphosphazene) and template in a low-boiling-point solvent on to the electrode surface; 3.preparation of composite membranes containing conductive material (graphite or carbon black), acrylic-type molecularly imprinted polymers (small particle size), and PVC as binder; and 4.in-situ polymerisation of a thin layer of acrylic imprinted polymer deposited on the electrode surface by spin coating.All the options evaluated offer the possibility of controlling electrode characteristics such as hydrophobic/hydrophilic character, permeability, or film thickness, which are essential for obtaining good sensor performance.     

Aligned silicon carbide nanowire crossed nets with high superhydrophobicity

Aligned silicon carbide nanowire crossed nets (a-SiCNWNs) were directly synthesized by using a vapor-solid reaction at 1100 degrees C. Zinc sulfide was used as catalyst to assist the growth of a-SiCNWNs with small size and crystal structure. After functionalization with perfluoroalkysilane, a-SiCNWNs showed excellent superhydrophobic property with a high water contact angle more than 156 +/- 2 degrees , compared to random nanowires (147 +/- 2 degrees ) and pure silicon wafers (101 +/- 2 degrees ). The topographic roughness and chemical modification with CF 2/CF 3 groups contributed the better superhydrophobicity. Furthermore, the as-grown SiCNWNs can be scraped off and coated on other substrates such as pure silicon wafers. The novel nanowire coating with good superhydrophobicity displays extensive applications in silicon-related fields such as solar cells, radar, etc.     

Patterning phase separation in polymer films with dip-pen nanolithography

We report a rapid-prototyping method for controlling nanoscale phase separation and pattern formation in conjugated polymer blend films using Dip-Pen Nanolithography (DPN). We use DPN to generate patterned alkylthiol monolayers with feature sizes down to 50 nm on gold surfaces and show how such patterns can nucleate the formation of lateral domains in blends of poly-3-hexylthiophene (P3HT) and polystyrene (PS) cast from solution. We show that this process can be used to probe phase nucleation at heterogeneous surface sites ranging in size from 50 to 750 nm, and that polymer features smaller than 150 nm in diameter can be achieved. We anticipate this method will be useful for studying polymer film responses to nanoscale surface fluctuations as well as for correlating nanoscale phase separation with optoelectronic processes in organic films used in light-emitting diode and photovoltaic devices.     

Photoactive additives for cross-linking polymer films: Inhibition of dewetting in thin polymer films

In this report, we describe a versatile photochemical method for cross-linking polymer films and demonstrate that this method can be used to inhibit thin polymer films from dewetting. A bifunctional photoactive molecule featuring two benzophenone chromophores capable of abstracting hydrogen atoms from various donors, including C-H groups, is mixed into PS films. Upon exposure to UV light, the bis-benzophenone molecule cross-links the chains presumably by hydrogen abstraction followed by radical recombination. Photoinduced cross-linking is characterized by infrared spectroscopy and gel permeation chromatography. Optical and atomic force microscopy images show that photocrosslinked polystyrene (PS) thin films resist dewetting when heated above the glass transition temperature or exposed to solvent vapor. PS films are inhibited from dewetting on both solid and liquid substrates. The effectiveness of the method to inhibit dewetting is studied as a function of the ratio of cross-linker to macromolecule, duration of exposure to UV light, film thickness, the driving force for dewetting, and the thermodynamic nature of the substrate.     

Electric conductivity of polymer films filled with magnetic nanoparticles

The conductivity of polymer composites with magnetic nanoparticles (MNP) containing magnetite and other MNP (Ni, Cu–Ni) in the layers and planar cells with Al electrodes is studied. For soluble polymers (polyvinylpyrrolidone and polyvinyl alcohol) containing 1–10 wt % of magnetite MNP, a substantial effect of MNP on surface conductivity is detected over a wide range (from 10^–10 to 10^–3 Ω^–1). It is shown that the addition of magnetite MNP not only results in a considerable change in cell conductivity, but also leads to its partially irreversible variation (by an order of magnitude or more) via minor modifications of the experimental conditions (temperature, electric field). For high-resistance samples with low probabilities of conducting chain formation, temperature current peaks are observed upon moderate heating (up to 350 K). These peaks are similar to the maxima observed upon polymer electret thermodischarges when the charges are captured by the deep centers associated with separate MNP or MNP aggregates. The type and position of the maxima are determined by the characteristics of the polymer matrix. For polyvinylpyrrolidone composites, the maxima are observed some time after heating (the echo effect). With composites based on solventborne polymers (polyalkanesterimides, soluble polyimide) and Ni, Cu–Ni MNP, no change in film conductivity measured electrophotographically is observed, due to the formation of a dielectric coating formed by polymer macromolecules adsorbed on the MNP surface. An explanation based on the possible formation of magnetic aggregates of magnetite MNP and conducting chains is proposed. Magnetic aggregation IPM is proposed as one way of controlling cell conductivity.