Molecular-level insight of gas transport in composite poly (4-methyl-2-pentyne) and nanoparticles of titanium dioxide

Composites are employed to treat gas mixtures and brilliant performance is observed, but few researchers have performed in-depth exploration of both bulk and interface behavior of penetrants in composites or given equations to correlate cavity size distribution, chain oscillation flexibility and transport properties. In the work, molecular dynamics (MD) method was employed to study the bulk and interface behavior of gas molecules in composite poly (4-methyl-2-pentyne) (PMP) and TiO₂ nanoparticles (PMPT). The amplitude of the chain oscillation and the cavity size distribution of PMPT and PMP were determined. Simulation results show that in PMPT penetrants have shorter residence time and jump length, than they do in PMP. Penetrants have higher diffusivity in PMPT than they do in PMP, because of higher amplitudes of chain oscillation and accessible cavity fraction for penetrans. In both PMPT and PMP, n-butane has larger permeability than methane, though the selectivity of n-butane over methane in PMPT is higher than that in PMP. Nonequilibrium MD simulation was performed to explore the interface property and gas molecules behavior in the interface region. The equations to predict diffusivity and permeability according to accessible cavity fraction and average amplitude of chain oscillation were developed successfully.