Films minces de cristaux liquides

Abstract : This thesis is dedicated to the wetting properties of silicon wafers covered by liquid crystals. We first present the study of a wetting transition taking place around the nematic-isotropic transition. We show that the evolution of the spreading parameter of isotropic drops in function of the temperature obeys a scaling law which is characteristic of second order phase transitions. In the close vicinity of the transition, it is shown that the specific organisation of the first molecular layers affects the wetting properties at a macroscopic scale. On the other side of the transition, ellipsometric measurements of the nematic drop's thickness steps allow us to emphasize the importance of the elastic properties of the liquid crystal in the wetting transition as suggested by the "elastic pancakes" model. Then we discuss the stability of spun cast nematic films in function of both their thickness and temperature. We show the existence of a marginal stability thickness, under which nematic films appear to be unstable. The temperature dependence of this stability thickness is identical to the one of the nematic order parameter. We also present a study of the dynamics of the surface instability that occurs for unstable films. It appears to be akin to spinodal decomposition in binary mixtures. Finally, experimental results about the spreading dynamics of smectic drops are confronted with success to the de Gennes-Cazabat model of the layered drops spreading.
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Theses
Fluid Dynamics [physics.flu-dyn]. Université Pierre et Marie Curie - Paris VI, 2001. French


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Contributor : François Vandenbrouck <>
Submitted on : Saturday, August 17, 2002 - 7:57:40 PM
Last modification on : Saturday, August 17, 2002 - 7:57:40 PM

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François Vandenbrouck. Films minces de cristaux liquides. Fluid Dynamics [physics.flu-dyn]. Université Pierre et Marie Curie - Paris VI, 2001. French. <tel-00001559>

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