Molecular dynamics simulation study of gas transport through chiral liquid crystalline monolayer

Molecular dynamics simulations were done for a chiral liquid crystalline (LC) monolayer with and without transmonolayer H₂ gas flow. The rotational dynamics of the monolayer LC molecule (MHPOBC) along its long-molecular axis was analyzed by tracing the orientations of the C = O bond close to the chiral part. We found that the reorientational motion along the molecular long-axis within the simulated time scale (10ns) was mostly not rotation but libration. We also found that the transmonolayer H₂ gas flow renders no apparent effects on the rotational motions of the MHPOBC molecules. Dependency of the MHPOBC rotational directions under the gas flow on the molecular chirality was not seen either. In contrast, marked chirality dependency was found in the asymmetry of the C = O orientational distributions that are oppositely biased each other between (S)- and (R)-MHPOBC. Resultant net polarization directions from these biased C = O distributions correspond to the experimentally reported spontaneous polarization (P_s) directions. It suggests that in our simulations, P_s and its direction were determineded as the biased distribution within much shorter time scale than that for the hindered rotation.