Binary separation in very thin nematic films: Thickness and phase coexistence - art. no. 125701

The behavior as a function of temperature of very thin films (10 to 200 nm) of pentylcyanobiphenyl on silicon substrates is reported. In the vicinity of the nematic-isotropic. transition we observe a coexistence of two region s of different thicknesses: thick regions are in the nematic state while th in ones are in the isotropic state. Moreover, the transition temperature is shifted downward following a 1/h(2) law (h is the film thickness). Microsc ope observations and small-angle x-ray scattering allowed us to draw a phas e diagram which is explained in terms of a binary first-order phase transit ion where thickness plays the role of an order parameter.