Liquid crystal alignment at macroscopically isotropic polymer surfaces: Effect of an isotropic-nematic phase transition
Autor: | Yuri Reznikov, Natalie Aryasova |
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Rok vydání: | 2015 |
Předmět: |
Phase transition
Materials science Condensed matter physics Isotropy 02 engineering and technology 021001 nanoscience & nanotechnology 01 natural sciences Thermotropic crystal Rubbing Condensed Matter::Soft Condensed Matter Temperature gradient Liquid crystal 0103 physical sciences Heat transfer Elasticity (economics) 010306 general physics 0210 nano-technology |
Zdroj: | Physical review. E. 94(3-1) |
ISSN: | 2470-0053 |
Popis: | We study the effect of an isotropic-nematic (I-N) phase transition on the liquid crystal alignment at untreated polymer surfaces. We demonstrate that the pattern at the untreated substrate in the planar cell where the other substrate is uniformly rubbed strongly depends on the temperature gradient across the cell during the I-N phase transition, being macroscopically isotropic if the untreated substrate is cooled faster, but becoming almost homogeneous along the rubbing direction in the opposite temperature gradient. We interpret the observed effect using complementary models of heat transfer and nematic elasticity. Based on the heat transfer model we show that the asymmetric temperature conditions in our experiments provide unidirectional propagation of the I-N interface during the phase transition and determine the initial director orientation pattern at the test's untreated surface. Using the Frank-Oseen model of nematic elasticity, we represent the three-dimensional director field in the nematic cell as a two-dimensional (2D) pattern at the untreated surface and perform 2D numeric simulations. The simulations explain the experimental results: Different initial director orientations at the untreated surface evolve into different stationary patterns. |
Databáze: | OpenAIRE |
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