The investigation of some liquid crystal-liquid interfaces by molecular dynamics simulation method

Adsorptions of two members of 4-n-alkyl-4'-cyanobiphenyls (nCB) with n=5 and 8 at the air-water interface were studied by detailed atomistic molecular dynamics (MD) simulations. For each mesogen, four systems containing different surface coverages were selected. The mass and number density profiles of the water and liquid crystal molecules and of several different atom types along the interface normal axis were presented. At the interface, the cyano groups tend to point toward the waterside of the interface, with the methyl groups pointing farther away from water. The thicknesses of the interface and the adsorbed layer were estimated by fitting the density profiles into a hyperbolic tangential and Gaussian functional form, respectively. The calculated orientational order parameters P2, P4 and P6 were generally much greater than the experimental data previously reported for the bulk phase, because of more organized structure of mesogens at the interface. The radial distribution function among different atoms, self-diffusion coefficients, tilt angles with respect to the monolayer normal and the histograms of the various quantities were calculated.