Y. Martinez et al., METASTABILITY OF FREELY SUSPENDED LIQUID-CRYSTAL FILMS, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 53(3), 1996, pp. 2466-2472
We investigate the conditions required for the existence of smectic-A
liquid-crystal films freely suspended in vapor. This work is based on
a molecular density-functional theory developed in earlier studies of
wetting and layering transitions of smectic-A films at Liquid-solid an
d liquid-vapor interfaces. It is emphasized that all freely-suspended
films are metastable with respect to either the absence of the film or
the formation of the bulk smectic phase, depending on the relative st
ability of the bulk vapor and smectic phases. Films containing differe
nt numbers of layers correspond to local minima of the grand canonical
potential, and are ''stabilized'' relative to each other by the prese
nce of sufficiently large metastability barriers. The disappearance of
these barriers corresponds physically to the ''rupturing'' of the fil
ms. It is demonstrated that surface enhancement of smectic ordering do
es not play an essential role in the existence of freely suspended fil
ms, but may influence the order of disappearance of the layer-layer me
tastability barriers on changing temperature. We relate these findings
to the results of recent experimental studies of ''layer thinning tra
nsitions'' in freely suspended films.