Non-affine structural evolution of soft colloidal crystalline latex films under stretching as observed via synchrotron X-ray scattering

A polymer dispersion consisting of soft latex spheres with a diameter of 135 nm was used to produce a crystalline film with face-centered cubic (fcc) packing of the spheres. Different from conventional small-molecule and hardsphere colloidal crystals, the crystalline latex film in the present case is soft (i.e., easily deformable). The structural evolution of this soft colloidal latex film under stretching was investigated by in-situ synchrotron ultra-small-angle X-ray scattering. The film exhibits polycrystalline scattering behavior corresponding to fcc structure. Stretching results not only in a large deformation of the crystallographic structure but also in considerable nonaffine deformation at high draw ratios. The unexpected nonaffine deformation was attributed to slippage between rows of particles and crystalline grain boundaries. The crystalline structure remains intact even at high deformation, suggesting that directional anisotropic colloidal crystallites can be easily produced.

Surface morphology evolution of a thin polymeric supramolecular film by tuning interactions

A polymeric supramolecule consisting of symmetric polystyrene-block-poly(4-vinylpytidine) (PS-b-P4VP), dodecylbenzenesulfonic acid (DBSA), and 3-pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology,of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)(1.0)(PDP)(1.0) matrix are observed for the as-cast film because the weight fraction, f(comb), of the P4VP(DBSA) (1.0)(PDP)(1.0) blocks is much higher than that of PS as a result of the non-covalent interactions of P4VP and DBSA and DBSA and PDR Upon annealing the PS-b-P4VP(1:1)(DBSA)(1.0)(PDP)(1.0) film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.

Solvent and polymer concentration effects on the surface morphology evolution of immiscible polystyrene/poly(methyl methacrylate) blends

The effects of solvent nature on the surface topographies of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend films spin-coated onto the silicon wafer were investigated. Four different solvents, such as ethylbenzene, toluene, tetrahydrofuran and dichloromethane, were chosen. They are better solvents for PS than that for PMMA. When dichloromethane, tetrahydrofuran and toluene were used, PMMA-rich phase domains protruded from the background of PS. When ethylbenzene was used, PS-rich phase domains elevated on the average height of PMMA-rich phase domains. In addition, continuous pits, networks and isolated droplets consisted of PS formed on the blend film surfaces with the decrease of polymer concentrations. The mechanism of the surface morphology evolution was discussed in detail.

Stress transfer and damage evolution simulations of fiber-reinforced polymer-matrix composites

The stress transfer from broken fibers to unbroken fibers in fiber-reinforced thermosetting polymer-matrix composites and thermoplastic polymer-matrix composites was studied using a detailed finite element model. In order to check the validity of this approach, an epoxy-matrix monolayer composite was used as thermosetting polymer-matrix composite and a polypropylene (PP)-matrix monolayer composite was used as thermoplastic polymer-matrix composite, respectively. It is found that the stress concentrations near the broken fiber element cause damage to the neighboring epoxy matrix prior to the breakage of other fibers, whereas in the case of PP-matrix composites the fibers nearest to the broken fiber break prior to the PP matrix damage, because the PP matrix around the broken fiber element yields. In order to simulate composite damage evolution, a Monte Carlo technique based on a finite element method has been developed in the paper. The finite element code coupled with statistical model of fiber strength specifically written for this problem was used to determine the stress redistribution. Five hundred samples of numerical simulation were carried out to obtain statistical deformation and failure process of composites with fixed fiber volume fraction.

Polymer concentration, shear and stretch field effects on the surface morphology evolution during the spin-coating

Polymer concentration and shear and stretch field effects on the surface morphology evolution of three different kinds of polymers (polystyrene (PS), polybutadiene (PB) and polystyrene-b-polybutadiene-b-polystyrene (SBS)) during the spin-coating were investigated by means of atomic force microscopy (AFM). For PS and SBS, continuous film, net-like structure and particle structure were observed at different concentrations. For PB, net-like structures were not observed and continuous films and radial array of droplets emerged. Moreover, we compared surface morphology transitions on different substrate locations from the center to the edge. For PS, net-like structure, broken net-like structure and irregular array of particles were observed. For SBS, net-like structure, periodically orientated string-like structure and broken-line structure appeared. But for PB, flower-like holes in the continuous film, distorted stream-like structure and irregular distributions of droplets emerged. These different transitions of surface morphologies were discussed in terms of individual material property.

Fabrication of a metalloporphyrin - Polyoxometalate hybrid film by a layer-by-layer method and its catalysis for hydrogen evolution and dioxygen reduction

Tetrakis (N-methylpyridyl) porphyrinato] cobalt (CoTMPyP) and 1:12 silicotungstic acid (SiW12) were alternately deposited on a 4-aminobenzoic acid (4-ABA)-modified glassy carbon electrode through a layer-by-layer method. The resulting organic-inorganic hybrid films were characterized by cyclic voltammetry (CV) and UV/vis absorption spectroscopy. We proved that the prepared multilayer films are uniform and stable. SiW12-containing multilayer films (SiW12 as the outermost layer) exhibit remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). The kinetic constants for HER were comparatively investigated at different layers Of SiW12/CoTMPyP multilayer film-modified electrodes by hydrogen evolution voltammetry. In addition, rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) voltammetric methods confirm that SiW12/CoTMPyP (CoTMPyP as the outermost layer) multilayer films catalyze almost a two-electron reduction of O-2 to H2O2 in pH 1-6 buffer solutions. Furthermore, P2W18/CoTMPyP films were also assembled, and their catalytic activity for HER is very different from that Of SiW12/CoTMPyP multilayer films.