Fabrication of superhydrophobic polymer films with hierarchical silver microbowl array structures

Flexible superhydrophobic polyvinyl alcohol (PVA) films with silver bowl-like array structure are fabricated based on the thermal evaporation with sphere monolayer as templates and the modification of 1H, 1H, 2H, 2H-perfluorodecanethiol on silver surface. The silver microbowl arrays were composed of silver nanoparticles with an average diameter size of ca. 10 nm. The polymer films exhibit excellent stability and remarkable superhydrophobicity with a high water contact angle (CA) of about 163° and a low sliding angle (SA) of less than 3°.     

Directed electrodeposition of polymer films using spatially controllable electric field gradients

We report a method for the directed electrodeposition of polymer films in various patterns using spatially controllable electric field gradients. One- and two- dimensional surface electric field gradients were produced by applying different potential values at spatially distinct locations on an electrode surface. Variations in the resulting local electrochemical potentials were used to spatially manipulate the rate of electrodeposition of several polymers. By controlling the electric field gradient in the presence of sequentially varying deposition solutions, complex polymer patterns could be produced. One-dimensional structures consisting of alternating bands of polyaniline and either poly(phenylene) oxide or poly(aminophenylene) oxide were produced, as well as more complex two-dimensional structures. Film characterization was achieved through optical imaging, UV-vis spectroscopy, and ellipsometry. Results indicate that this directed deposition technique is a simple strategy to create complex, millimeter-sized surface patterns of electrodeposited materials.     

Preparation of functionally gradient fluorocarbon polymer films by plasma polymerization of NF3 and propylene

Fluorocarbon polymer films were prepared by plasma polymerization using nitrogen trifluoride (NF₃) and propylene as starting materials. To improve their adhesiveness to substrates, a novel functionally gradient film in which the content of fluorine decreased continuously from the surface to the interior was prepared by changing source gas composition during deposition. This film had a smooth and pinhole-free surface, and had a high contact angle (110°) for water drop. In addition, it showed good adhesion to a glass substrate. © 1996 John Wiley & Sons, Inc.     

FTIR-microscopy versus FTIR-ATR-spectroscopy for the analysis of multilayer polymer films

Transmission FTIR-microscopy can be applied successfully for routine analysis of the different areas of a multilayer polymer film as used in packaging industry or for new flame resistant airplane wall covers and for other high tech applications. Using a microtome cut of approx. 10m thickness one can get a lateral resolution of the same size and spectra with excellent S/N-ratio. The method is superior as compared to the standard ATR-technique both in information delivered (micro-domains rather than areas of 1 cm², better S/N-ratio) and ease of sample preparation. A practical comparison is described.     

Combining layer-by-layer assembly with electrodeposition of silver aggregates for fabricating superhydrophobic surfaces

Taking advantage of the stability and penetrability of layer-by-layer (LbL) films, we develop a novel method to fabricate a branchlike structure of Ag aggregates on the matrix of a LbL polyelectrolyte multilayer by an electrodeposition technique. The morphology of Ag aggregates can be adjusted by electrodeposition time and potential. Moreover, after further chemisorption of a self-assembled monolayer of n-dodecanethiol, the as-prepared surface becomes superhydrophobic with a contact angle as high as 154 degrees and a tilt angle lower than 3 degrees.     

Factors in liquid crystal photoalignment on polymer films: photoorientation versus self-assembly

We demonstrate that photostimulated self-assembly, running in parallel with molecular photoorientation in the top layer of the aligning polymer film, breaks the bulk molecular order mainly determined by the symmetry of irradiation. This may substantially modify liquid crystal (LC) alignment. Depending on the chemical composition of the liquid crystal, the self-assembled layers may influence either homeotropic or planar LC alignment with extremely weak azimuthal anchoring. Effective self-assembly occurs in polymers having side chain chromophores with flexible spacers and polar terminal groups.     

Role of polymer synthesis conditions for the copper electrodeposition in polyaniline

Polyaniline (PAN) layers are electrochemically synthesised by three different procedures – potentiostatic (PS), potentiodynamic (PD) and pulse potentiostatic (PP). Galvanostatic copper deposition and subsequent oxidation of copper species are studied on the three types of PAN layers. A marked difference in the deposition/dissolution behaviour is found depending on the type and redox state of PAN. Copper reduction is easily initiated at low overpotentials at oxidised PS and PP PAN specimens, whereas for oxidised PD layers copper deposition needs higher overpotentials. This difference is discussed in terms of various reduction behaviours of the three types of PAN. In general reduced PANs strongly inhibit copper nucleation and growth. Still a marked difference in the metal deposition on reduced PD and PP PANs on the one hand and reduced PS PAN on the other exists. This difference is related to the varying amount of defects in the three polymer structures, evidenced by SEM observation of Cu/PAN-coated electrodes.     

Wetting properties of the multiscaled nanostructured polymer and metallic superhydrophobic surfaces

A superhydrophobic surface is produced from industrial grade polymer materials. The surface comprises partly disordered triple-scaled arrays of polyvinylidene fluoride (PVDF) globules. An inherently superhydrophobic metallic surface is produced with polymer template. The mathematical model based on the Cassie-Baxter hypothesis of air trapping under a water drop is built, which gives the apparent contact angle on the manifold-scaled interface. The presence of several scales itself is not a sufficient condition of hydrophobicity of inherently wettable surfaces. The geometrical features favoring the increase of the vapor-water interface fraction are necessary for this phenomenon.     

Nanomechanical properties in ultrathin polymer films: Measurement on rectangular versus circular bubbles

Prior studies of inflation of circular membranes of ultrathin polystyrene (PS) films have evidenced a reduced glass transition temperature (T_g) and rubbery stiffening, whose origins remain unclear. Here, we describe results from inflation of rectangular, ultrathin films of the same PS material. The bubble shapes obtained from the experiment are consistent with finite element (FE) simulations. The accuracy of three approximate solutions for modulus obtained from the inflation of the thin, rectangular films was evaluated by comparison with FE analysis. The best among the three solutions was used to determine the creep compliance and rubbery stiffness of the thin films. It is found that the reduction of T_g and the rubbery stiffening for rectangular bubbles are consistent with results obtained using circular bubbles, although there is some indication that the rectangular bubbles give somewhat greater rubbery stiffening. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Influence of electrodeposition conditions on the properties of CdTe films

The results of the influence of electrodeposition conditions on the structural, compositional, optical, and photoelectrochemical properties of CdTe thin films deposited in one-step electrochemical method are presented. The CdTe films were prepared electrochemically from aqueous acidic solution with low ratios of Cd²⁺ ions to Te(IV) ions concentration. Instead of commonly used TeO₂, water-soluble Na₂TeO₃ was used as a source of tellurium ions. The cathodic deposition of CdTe was performed at different constant potentials from solutions containing different cadmium and tellurium ions concentration. As-deposited CdTe thin films were studied by different analytical techniques. The X-ray photoelectron spectroscopy spectra exhibited CdTe formation on the electrode with some amount of tellurium oxides and cadmium oxides. The best quality CdTe deposits, free of TeO₂, were formed in bath containing excess of Cd²⁺ ions and at the potential of ?0.65 V vs. saturated calomel electrode, slightly more positive than E _eq of Cd/Cd²⁺ system. Structural X-ray diffraction studies revealed polycrystallinity of deposits with the highest content of the (111)-oriented cubic (111) form. Optical band gap energy values were found in the range from 1.36 to 1.6 eV for CdTe films prepared at various synthesis conditions. The preliminary photoelectrochemical studies have shown that the variation of the deposition potential as well as bath composition leads to the formation of p- or n-type CdTe films. As-deposited CdTe films were not stable in polysulfide solution under illumination.     

Interfacial stability of electrodeposition of cuprous oxide films

Experiments on deposition of Cu(2)O films from basic copper sulfate solution show that copper also deposits. At low, but basic values of pH only copper deposits and at high pH only cuprous oxide deposits. In the intermediate range where both compete the system shows oscillations at "constant current." Linear stability analysis has been conducted for such an electrochemical cell to show that oscillations can take place in the parameter space identified in the experiments. The results are keeping with most of the experimental observations, which are many, but not with all. The physical mechanisms behind the oscillations are explained in terms of competing reactions.     

Synthesis of nanostructured films from template electrodeposition technique

In this report, the use of a simple and versatile technique of templated electrodeposition through colloidal templates to produce nanostructured films of Pt and Au with regular submicron spherical holes arranged in a hexagonal close-packed structure is described. The templates were produced by self assembly of a monodispersed suspension of polystyrene spheres on gold substrates using capillary forces. The self assembly process was modified through the chemical modification of the gold substrate with cysteamine thiol. Films of Pt and Au were prepared by electrochemical deposition through the template. The electrochemical deposition charge and the current time curve were used to control the film height with a precision of approximately 10 nm. The colour of the nanostructured films changed as the film thickness was changed. On the other hand, high surface area of the nanostructured Pt film on top of the gold substrate was calculated using electrochemical cyclic voltammogram. About 55 roughness factor was obtained. SAXS measurements showed strong scattering at low angles indicating the presence of a well-ordered mesostructure.     

Solvothermal synthesis of nanoporous polymer chalk for painting superhydrophobic surfaces

Reported here is a facile synthesis of nanoporous polymer chalk for painting superhydrophobic surfaces. Taking this nanoporous polymer as a media, superhydrophobicity is rapidly imparted onto three typical kinds of substrates, including paper, transparent polydimethylsiloxane (PDMS), and finger skin. Quantitative characterization showed that the adhesion between the water droplet and polymer-coated substrates decreased significantly compared to that on the original surface, further indicating the effective wetting mode transformation. The nanoporous polymer coating would open a new door for facile, rapid, safe, and larger scale fabrication of superhydrophobic surfaces on general substrates.     

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.     

Markedly controllable adhesion of superhydrophobic spongelike nanostructure TiO2 films

A simple electrochemical and self-assembly method was adopted for the fabrication of superhydrophobic spongelike nanostructured TiO2 surfaces with markedly controllable adhesion. Water adhesion ranging from ultralow (5.0 microN) to very high (76.6 microN) can be tuned through adjusting the nitro cellulose dosage concentrations. The detailed experiments and analyses have indicated that the significant increase of adhesion by introducing nitrocellulose is ascribed to the combination of hydrogen bonding between the nitro groups and the hydroxyl groups at the solid/liquid interfaces and the disruption of the densely packed hydrophobic 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PTES) molecule. A mechanism has been proposed to explain the formation of superhydrophobic TiO2 films with distinct adhesion.     

Direct electrodeposition of PbTe thin films on n-type silicon

High quality lead telluride thin films were directly deposited onto n-type silicon (1 0 0) substrates by electrodeposition at room temperature. The deposition mechanism was studied using cyclic voltammetry. The films were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, and Fourier transform infrared spectroscopy. The results indicated that the deposited PbTe films exhibited a polycrystalline rock salt structure and good optical properties with a direct band gap of 0.31 eV.