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The miscibility and mechanical properties of poly vinyl alcohol (PVA) and poly acrylic acid (PAA)-composited membranes were studied with molecular simulation. The Flory–Huggins parameters (δ) were calculated to prove the good miscibility of PVA and PAA. The radial distribution functions of hydroxyl and carboxyl atoms and the average number of H-bonds were observed to indicate the degree of physical cross-linking between PVA and PAA. The influences of intermolecular physical cross-linking on the glass transition temperature and mechanical properties were estimated. The results revealed that the PVA/PAA membrane with a composition of 2:3 has the best plastic properties, which exhibits a good application value. All of the simulated results showed good agreement with the experimental data. It indicates that the method presented in this work has a promising application prospect.

A rigorous approach is proposed to model the mean ion activity coefficient for strong electrolyte systems using the Poisson–Boltzmann equation. An effective screening radius similar to the Debye decay length is introduced to define the local composition and new boundary conditions for the central ion. The crystallographic ion size is also considered in the activity coefficient expressions derived and non-electrostatic contributions are neglected. The model is presented for aqueous strong electrolytes and compared with the classical Debye–Huckel (DH) limiting law for dilute solutions. The radial distribution function is compared with the DH and Monte Carlo studies. The mean ion activity coefficients are calculated for 1:1 aqueous solutions containing strong electrolytes composed of alkali halides. The individual ion activity coefficients and mean ion activity coefficients in mixed solvents are predicted with the new equations.

It is well known that 4,4'hexafluoro isopropylidene-phthalic anhydride(FDA) has higher permeability and selectivity. It is contributed to –CF group contained in polyimide structure material. In this study, the diffusion properties of a,w-bis(3-aminopropyldimethyl) oligodimethylsiloxane (ODMS) fragment impact on 6FDA were studied. Molecular simulation techniques and Grand canonical Monte Carlo(GCMC)calculations were adopted for predicting the permeability of C2H5OH and H2O in the three new polymers membranes. The membranes considered in this work were synthesized from 6FDA and ODMS. The sorption and diffusion properties of C2H5OH and H2O were calculated. The results show that the 6FDA/6ODMS presents higher permeability than 6FDA/2ODMS and 6FDA/4ODMS. With the longer of ODMS segments in the repeat units, the permeability and selectivity of C2H5OH/H2O increase in the order of 6FDA/2ODMS< 6FDA/4ODMS< 6FDA/6ODMS. The length of molecular chains becomes longer with the ODMS fragments increased, which leads to the gap between the molecular chains becoming larger. Due to the free volume in the system increases, it is more conducive to the larger molecular volume through the membrane. Hence, it can be predicted that the 6FDA/6ODMS is the best for the separation of C2H5OH/H2O.