Binary separation in very thin nematic films: thickness and phase coexistence.
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 regions of different thicknesses: thick regions are in the nematic state while thin ones are in the isotropic state. Moreover, the transition temperature is shifted downward following a 1/h(2) law ( h is the film thickness). Microscope observations and small-angle x-ray scattering allowed us to draw a phase diagram which is explained in terms of a binary first-order phase transition where thickness plays the role of an order parameter.
van Effenterre
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Physique de la Matière Condensée, Collège de France, URA 792 du CNRS, 11 place Marcelin Berthelot, 75005 Paris, France.
Ober
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Valignat
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MP
Cazabat
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