Molecular organization in freely suspended nano-thick 8CB smectic films. An atomistic simulation
Résumé
We present an atomistic molecular dynamics simulation of freely suspended films of the smectic liquid crystal 8CB formed by n(l) = 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 n(l), the system prefers to self-assemble in (n(l) + 1)/2 bilayers, with an increase of surface tension with respect to even n(l) 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.