Computer simulations play an important role in designing new polymers as well as in predicting properties of existing polymers. In this paper, the blend compatibility of poly(vinyl alcohol) (PVA) with poly(methyl methacrylate) (PMMA) was studied over the wide range of compositions allowed by the atomistic and mesoscopic simulation methods. The Flory-Huggins interaction parameter, chi, of the blends computed using the atomistic simulation confirmed the blend compatibility for compositions containing >60 wt % of PVA. This observation was further supported by differential scanning calorimetric experiments. Solubility parameters of the polymers obtained from the simulation procedure were in good agreement with those of the literature data. Simulation results were further supported by the spectral and solution property measurements. From the atomistic simulations, chi versus concentration plots were constructed, which showed trends similar to those experimentally measured melting temperature versus concentration. The chi values for the blends, which satisfied the criteria of miscibility of two polymers by the atomistic simulation, agreed quite well with the solubility criteria related to order parameters calculated from the mesoscopic simulation. Kinetics of phase separation was examined via density profiles calculated using the MesoDyn approach for incompatible blends. The length and time scales spanned by these simulations were found to be relevant to the real application scales. The free energy computed in the mesoscopic simulation for blends reached equilibrium, particularly when the simulation was performed at a higher time step, indicating the stability of the blend system at certain compositions.

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ABSTRACT:The blend miscibility of poly(vinyl alcohol) and poly(methyl methacrylate) in N,NЈ-dimethylformamide solution was investigated by viscosity, density, ultrasonic velocity, refractive index, and UV and fluorescence spectra studies. Differential scanning calorimetry and scanning electron microscopy were used to confirm the blend miscibility in the solid state. Blends were compatible when the concentration of poly(vinyl alcohol) was greater than 60 wt %.

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Composite membranes of sulfonatedpoly(ether ether ketone) (sPEEK) containing nascent and modified silicotungstic acid (STA) nanoparticles were tested for pervaporation (PV) separation of waterisopropanol mixtures. The performance of filler loaded composite membranes was better than that of nascent polymer membranes. The chemically modified STA containing membranes showed improved PV performance compared to those of nascent STA loaded membranes. This effect is attributed to leaching of STA during the PV cycles. The leaching effect was reduced after modification of STA with cesium carbonate. Among all the composite membranes prepared by the solution casting method, the membrane containing 7 wt% modified STA gave the highest PV separation performance compared to those containing 3, 5 and 10 wt% STA. The PV performance of the 7 wt% STA loaded membrane was further tested as a function of feed water composition from 10 to 25 wt% and a temperature range of 30-60 C. Characterization of the membranes was done by universal testing machine (UTM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The PV results have been explained in terms of sorption-diffusion principles and Arrhenius activation parameters.