Experimental study of hybrid nematic wetting films

• Published in: Advances in colloid and interface science 2011-10, Vol.168 (1), p.29-39
• Main Authors: Cazabat, A.M., Delabre, U., Richard, C., Yip Cheung Sang, Y.
• Format: Article
• Language: English
• Subjects: Deposition; Distortion; Elastic anisotropy; Film coexistence; Film thickness; Glycerols; Instability patterns; Liquid crystals; Liquids; Nematic; Nematic elasticity; Nematic order parameter; Physics; Thin wetting films
• ISSN: 0001-8686; 1873-3727
• DOI: 10.1016/j.cis.2011.01.001

Liquid crystal layers, with thickness less than 1 μm, are deposited on isotropic – solid or liquid – substrates and investigated in the bulk nematic range of temperatures. The boundary conditions at interfaces are antagonist ones, therefore the layers are distorted due to nematic elasticity. These films are referred to as “hybrid nematics”. The consequences are complex. First, a forbidden range of film thickness is observed, depending only on temperature. Second, the anisotropy of the elastic response gives rise to striking stripe patterns in the thicker films. This behavior is common to several members of the series of n-cyanobiphenyls deposited on oxidized silicon wafers, water and glycerol. The aim of the study is to collect data, and determine which ones find a place within a common theoretical framework. [Display omitted] ► Nematics deposited on substrates with hybrid anchoring may show film coexistence. ► Thicker films may be striped due to the anisotropy of nematic elasticity. ► Available theoretical models account partly on the thicker films properties. ► Coexistence of molecular and mesoscopic thinner films occurs close to NI transition. ► The structure of mesoscopic thinner films is still largely unknown.