Anomalous melting of overheated smectic films

Abstract

ABSTRACTThe formation of droplets of a nematic phase in free-standing smectic films (FSSFs) overheated above the temperature of the bulk smectic–nematic transition is studied theoretically. Contrary to the bulk systems the film melting is strongly influenced by its confinement between two free surfaces. By using the general thermodynamic approach to the stability of FSSF, we determined the gain in the free energy related with the formation of the nematic droplets, the value of the critical work and the critical size of the drops. The necessary material for initial drops growth is provided by the thermally exited dislocation loops. The further drops growth occurs through merging of the droplets of different size under influence of the capillary forces. These forces arise due to gradients of the surface energy of the film around the drops. At smaller distances an additional interaction of the fluctuation origin appears (pseudo-Casimir), which also favour the drops coalescence. The scenarios of the drop size evolution and of the dynamics of the process are in good agreement with experiments.