Nucleation of focal conic domains in smectic A liquid crystals
| Autor: | V. M. Pergamenshchik, Oleg D. Lavrentovich, M. Kléman |
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| Rok vydání: | 1994 |
| Předmět: | |
| Zdroj: | Journal de Physique II. 4:377-404 |
| ISSN: | 1286-4870 1155-4312 |
| DOI: | 10.1051/jp2:1994135 |
| Popis: | The first-order structural transitions caused by an external magnetic field or by a surface anchoring are considered for a smectic A liquid crystal in the restricted geometry of a flat cell. The transition occurs by nucleation of focal conic domains. The free energy of the system is calculated as a function of the order parameter ρ= domain radius/cell thickness for finite value of the splay (K) and a saddle-splay ($\bar{K}$) elastic constants and the anchoring coefficient. For small ρ the behavior of the system is defined by the balance of the stabilising elastic term and destabilising field (or anchoring) term. Homogeneous nucleation from ideal uniform state is hindered by high energetic barrier unless $\bar{K}$ is positive and comparable (or larger) than K. A few possible scenarios of heterogeneous nucleation have been considered, among them the nucleation at local layer undulations and the nucleation at field-induced dislocations. The most effective and general scenario is the nucleation at distortions (dislocations) caused by bulk or surface irregularities. The expansion of the domain (ρ≫1) is governed by the balance between the field and surface anchoring and does not depend directly on the elastic constants. The saturation field that provides the domain expansion can be smaller than the threshold field for other known mechanisms of the SmA instabilities. |
| Databáze: | OpenAIRE |
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