Effect of polymer-filler surface interactions on the phase separation in polymer blends

For the blends of chlorinated polyethylene and copolymer of ethylene with vinyl acetate, the effect of the introducing filler (fumed silica) on the phase behavior of the blends was investigated. It was found that introducing filler in polymer blends depending on its amount lead either to the increase or to the decrease in the temperature of phase separation. At the filler concentration where both components transit into the state of a border layers, the phase separation temperature increases. This effect was explained by the change of the total thermodynamic interaction parameter in the ternary system polymer-polymer-filler. At lower concentration of a filler, the possible effect is the redistribution of the blend components according to their molecular masses between filler surface (in the border layer) and in the bulk that may diminish the phase separation temperature.Effect of the filler on the phase behavior was explained by the simultaneous action of two mechanisms: by changing the thermodynamics of interaction near the surface due to selective adsorption of one of the components and by the redistribution of components according to their molecular masses between the boundary region (near the surface) and in the matrix.The measurements of the kinetics of phase separation and calculation of the parameters of the activation energy are in agreement with proposed mechanisms.     

Phase separation kinetics and morphology in a polymer blend with diblock copolymer additive

The phase diagram for a low molecular weight blend of deuterated polystyrene (PSD) and polybutadiene (PB) was determined by temperature jump light scattering (TJLS) measurements and phase contrast optical microscopy (PCOM). The PSD/PB blend exhibited upper critical solution temperature behavior, and the critical temperatures measured by these two techniques were consistent. Upon addition of 0 to 0.12 mass fraction of a comparable molecular weight PSD-PB symmetric diblock copolymer, a linear decrease in the phase transition temperature was observed with increasing diblock copolymer content. At a constant, shallow quench depth, the kinetics of phase separation via spinodal decomposition as measured by TJLS were greatly retarded by the presence of the copolymer. Additionally, the time dependence of the concentration fluctuation growth did not seem to follow a universal functional form anywhere in the accessible q range when the diblock was present. The results of morphology study of the blends in the late stage of phase separation by PCOM also indicated that the phase separated domain sizes did not grow to the same size for a given annealing time as diblock content increased.     

Phase diagram of different epoxy-amine precursors modified with a thermoplastic: Effect of structure of epoxy-amine system on miscibility

The miscibility of a thermoplastic with the precursors of different epoxy-amine systems was analyzed thermodynamically in which the dependence of interaction parameter on temperature and composition χ (T, ?) and the polydispersity of components were considered. The epoxy-amine precursors were different only in the nature of amino groups, which were provided by a monoamine and a diamine in different proportions. Cloud-point curves were measured for five unreacted modified systems resulting that miscibility of the system increased with the proportion of monoamine. The thermodynamic analysis was realized in two steps: first, the model was applied to each system individually and secondly, a general equation for χ (T, ?) depending on the monoamine-diamine proportion was searched and used to analyze all systems together. Theoretical calculations of cloud-point curves, shadow curves, spinodal curves, critical points, vitrification curves and species distributions were realized and discussed for those systems.     

Compatibilization mechanisms of nanoclays with different surface modifiers in UCST blends: Opposing effects on phase miscibility

The effects of organically modified and pristine nanoclays on the kinetics of thermodynamic equilibrium state attainment for semicrystalline binary blends of polyethylene (PE)/ethylene-vinyl acetate copolymer (EVA) have been investigated. Due to the non-equilibrium compatibilization mechanism, intercalated organoclay results in a slower rate of phase miscibility change at lower annealing temperatures, thereby worsening the PE/EVA compatibility state. In contrast to poorly dispersed pristine nanoclay, the homogeneous state is obtained at higher or equal rates by adding organoclay at higher annealing temperatures because of the dominant role of nanofiller equilibrium compatibilization mechanism. Phase diagrams of these UCST blends determined by a dynamic method shifts to higher temperatures by the incorporation of nanofillers and the unexpected reduction in miscibility window area is much more noticeable for nanocomposites having highly restricted molecular movements. This can verify that dynamic methods lose their efficiency for measuring the equilibrium phase diagram of polymer blends containing nanoparticles.     

Spinodal decomposition as a probe to measure the effects on molecular motion in poly(styrene-co-acrylonitrile) and poly(methyl methacrylate) blends after mixing with a low molar mass liquid crystal or commercial lubricant

The effects on molecular motion observed through early stage phase separation via spinodal decomposition, in melt mixed poly(styrene-co-acrylonitrile) (SAN) containing 25% by weight of acrylonitrile (AN) and poly(methyl methacrylate) (PMMA) (20/80 wt%) blends after adding two low molar mass liquid crystals (CBC33 and CBC53) and two lubricants (GMS and zinc stearate) were investigated using light scattering techniques. The samples were assessed in terms of the apparent diffusion coefficient (D_app) obtained from observation of phase separation in the blends. The early stages of phase separation as observed by light scattering were dominated by diffusion processes and approximately conformed to the Cahn-Hilliard linearised theory. The major effect of liquid crystal (LC) was to increase the molecular mobility of the blends. The LC generally increased the Cahn-Hilliard apparent diffusion coefficient, D_app, of the blend when added with concentrations as low as 0.2 wt%. GMS and zinc stearate can also improve the mobility of the blend but to a lesser extent and the effect does not increase at higher concentration. On the other hand, the more LC added, the higher the mobility. In all systems the second derivative of the Gibbs free energy becomes zero at the same temperature. The improved mobilities therefore seem to arise from changes in dynamics rather than thermodynamic effects.     

Diffusion in a mesoporous silica membrane: Validity of the Knudsen diffusion model

Experimental permeance data for several light gases in a mesoporous silica membrane are analyzed in detail and shown to conform closely to the Knudsen diffusion model. The results of this study do not support the conclusions drawn from recent molecular simulations concerning the inadequacy of the Knudsen model.     

Reduction of metal ions in dilute solutions using a GBC-reactor Part II: Theoretical model for the hydrogen oxidation in a gas diffusion electrode at relatively low current densities

The GBC-reactor is based on the combination of a gas diffusion anode and a porous cathode. A theoretical model for gas diffusion electrode, valid at relatively low current densities, is derived. This is based on the pseudohomogeneous film model including an approximation of the Volmer–Tafel mechanism for the hydrogen oxidation kinetics. Results show a severe mass transfer limitation of the hydrogen oxidation reaction inside the active layer of the gas diffusion electrode, even at low current densities. Empirical formulae are given to estimate whether leakage of dissolved hydrogen gas into the bulk electrolyte occurs at specific process conditions. A simplified version of the model, the reactive plane approximation, is presented.     

Water diffusion and permeability in unsaturated polyester resin films characterized by measurements performed with a water‐specific permeameter: Analysis of the transient permeation

A water‐specific permeameter was developed to study water diffusion in an unsaturated polyester; these polyesters are often used as high‐barrier materials. Low water enrichment of a dry sweeping gas is measured via the dew point temperature, with two hygrometers, one of which is used because of its fast response and the other because of its accuracy. This high‐performance device is just as suited to pervaporation as to permeation tests and allows the transient and stationary fluxes to be characterized. At first sight, the experimental data seem in good agreement with D = D₀e^γC. However, a more thorough study has shown a time‐dependence of D. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3380–3395, 1999     

Confined crystallization phenomena in immiscible polymer blends with dispersed micro-and nanometer sized PA6 droplets part 4: polymorphous structure and (meta)-stability of PA6 crystals formed in different temperature regions

The genesis and stability of different PA6 crystalline polymorphs, dispersed as micro- and submicrometer sized droplets inside an amorphous polymer matrix, are discussed over a very broad temperature range. Different PA6 droplet sizes lead to different PA6 crystallization events in a 100 °C wide temperature window that extends down to 85 °C. Static WAXD and DSC experiments on micrometer sized PA6 droplets indicate the formation of a stable γ-crystal phase in the region between 175 and 130 °C. Sub-micrometer sized PA6 droplets only crystallize at 85 °C in the β-phase. Upon heating above the PA6 glass transition, these crystals progressively increase their perfection and ultimately transform into the α-phase around 170 °C.