Diffusion behavior of benzene/cyclohexane molecules in poly(vinyl alcohol)-graphite hybrid membranes by molecular dynamics simulation

Understanding the effects of incorporated inorganic particles in organic–inorganic hybrid membranes at molecular level is crucial to design hybrid membranes with tailored structure and desired properties. In this study, molecular dynamics simulation has been employed to investigate the effects of graphite particle on the diffusion behavior of benzene and cyclohexane in poly(vinyl alcohol)-graphite hybrid membranes. Firstly, the non-bonding interaction energies between PVA polymer and graphite particle with different amount of hydroxyl and carboxyl groups were calculated by DREIDING force field. Next, polymer chain mobility was analyzed by mean-square displacement (MSD) and glass transition temperature (Tg)Tg), and found that incorporation of graphite particle into PVA increased the polymer chain mobility. Free volume characteristics of membranes were investigated by Connolly surface, and found that free volumes in PVA-graphite hybrid membranes were larger than those in PVA control membranes. This simulation result showed the same tendency with the PALS measurement. Finally, the diffusion coefficients of benzene and cyclohexane in the membranes were calculated by Einstein relation, and found that the diffusion coefficients in hybrid membranes were larger than those in the control membrane. Furthermore, it was found that the diffusion coefficients of benzene and cyclohexane in the membranes exhibited exponential relation with the inverse fractional free volumes and agreed well with the free volume theory.