Dr. Apala Majumdar: Multistability in planar liquid crystal wells

Datum objave: 20. 2. 2015
Seminar fizike mehkih snovi
Ponedeljek, 23. 2. 2015, ob 14:15 v predavalnici F2, FMF, Jadranska 19, Ljubljana
 
Multistability in planar liquid crystal wells

Dr. Apala Majumdar
University of Bath, United Kingdom


We numerically model a multistable liquid crystal device reported by Tsakonas et. al in 2007. This device comprises a periodic array of micron-scale square or rectangular shallow wells filled with nematic liquid crystal material and the well surfaces are treated to induce planar boundary conditions. We model the nematic well configurations within the celebrated Landau-de Gennes theory. We work with two key parameters in the problem: the well cross-sectional length and the surface anchoring strength. For small nano-scale wells, we find a new biaxial order reconstruction pattern. This two-dimensional order reconstruction pattern has not been previously reported in the literature and can be interpreted as a novel defect structure in nano-scale systems. For large micron-scale wells and relatively strong anchoring, we find six distinct stable states, two diagonal states and four rotated states and study the multiplicity of solutions as a function of the anchoring strength. We compute the transition pathways between distinct stable equilibria, the optimal transition pathways and the energy landscape of these micron-scale wells. There are multiple transition pathways between stable equilibria, mediated by multiple defects in some examples, and the transition pathways are sensitive to the anchoring strength in the weak anchoring regime. This is joint work with Chong Luo, Radek Erban, Samo Kralj and Halim Kusumaatmaja.