Directional Gas Diffusion in Liquid Crystal-Doped Cellulose Triacetate Membranes: Insights from Molecular Dynamics and Time-Lag Measurements

Cellulose triacetate membranes incorporating liquid-crystal additives have experimentally demonstrated enhanced gas transport, yet the molecular origins of diffusion anisotropy remain unclear. In this work, molecular dynamics simulations are combined with experimental diffusivity measurements to elucidate the role of mesogenic ordering on gas diffusion in CTA/5CT hybrid membranes. Directional diffusion coefficients parallel and perpendicular to the nematic director, together with nematic order parameters obtained from Q-tensor analysis, were evaluated for CO2 and H2 over LC loadings of 1 to 10 wt % and temperatures of 25, 35, and 50 °C. The simulations reveal strong, anisotropic diffusion for CO2 at 25 °C, which collapses near the nematic–isotropic transition, while H2 diffusion remains weakly anisotropic. Comparison with experimental diffusivities shows consistent trends in magnitude, LC-loading, and temperature dependence. These results establish a direct structure–diffusivity relationship in CTA/LC membranes and demonstrate how mesogenic phase behavior can be exploited to modulate gas transport mechanisms.