Molecular organization in freely suspended nano-thick 8CB smectic films. An atomistic simulation.

We present an atomistic molecular dynamics simulation of freely suspended films of the smectic liquid crystal 8CB formed by nl = 2, 3,…,10, 20 theoretical monolayers, determining their orientational and positional order as a function of the film thickness. We find that films are always composed by bilayers of antiparallel molecules, and that in the case of odd nl, the system prefers to self-assemble in (nl + 1)/2 bilayers, with an increase of surface tension with respect to even nl samples. We also show that external layers have higher positional and orientational order, and that upon heating the disordering of the system proceeds from the inside, with the central layers progressively losing their smectic character, while the external ones are more resistant to temperature changes and keep the film from breaking.

An atomistic description of the nematic and smectic phases of 4-n-octyl-4' cyanobiphenyl (8CB).

We report the results of atomistic molecular dynamics simulations of 4-n-octyl-4' cyanobiphenyl (8CB) on samples of 750 and 3000 molecules showing the spontaneous formation of the nematic phase and then of smectic layers by gradually cooling down from the isotropic phase. Orientational, positional, and mixed order parameters, layer spacing, translational diffusion tensor components and their temperature dependence are reported. A detailed comparison with available experimental data validates the model and force field employed and clarifies the molecular organization of this important liquid crystal often used as reference smectic material.