Coupling between the nematic/isotropic transition and a thickness transition: A theoretical approach

• Published in: Europhysics letters Vol. 62; no. 4; pp. 526 - 532
• Main Authors: Effenterre, D. van, Valignat, M. P, Roux, D
• Format: Journal Article
• Language: English
• Published: Les Ulis IOP Publishing 01.05.2003; EDP Sciences; EDP sciences
• Subjects: 61.30.Pq; 64.70.Md; 68.60.-p; Condensed matter: structure, mechanical and thermal properties; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Physics; Specific phase transitions; Transitions in liquid crystals; Thickness; Mean-field theory; Confinement; Phase diagrams; Phase transformations; Pinning; Theoretical study; Free surface; Liquid crystals; Liquid nematic transformation
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/epl/i2003-00375-2

In this letter, we develop a theoretical model of the effect of a free surface on the nematic-to-isotropic phase transition in a confined geometry. Simply by coupling a bulk first-order phase transition with a thickness-dependent elastic distortion field in a Landau-like description, the model predicts a coexistence at equilibrium between the isotropic and the nematic phases at two different thicknesses. A phase diagram is constructed in the temperature-thickness plane and a comparison is given with experimental results obtained on thin films (van Effenterre D., Ober R., Valignat M. P. and Cazabat A. M., Phys. Rev. Lett. 87(2001) 125701).