Surface viscosity and reorientation process in an asymmetric nematic cell

Abstract

2010) Surface viscosity and reorientation process in an asymmetric nematic cell, Liquid Crystals, 37:12, 1559-1568,The influence of surface viscosity and anchoring energy on the reorientation process of a nematic liquid crystal cell is theoretically investigated. The cell is a slab of thickness, d, whose limiting surfaces are characterised by different anchoring strengths and present easy directions parallel to the bounding surfaces, changing with time due to some external action. The exact space-time profile of the director angle is obtained by means of integral transform techniques and a Green function approach. From this formalism, the time dependence of the optical path difference is exactly determined and its behaviour is analysed in connection with the presence of surface viscosity and different anchoring energies. The problem is also exactly solved in the presence of a constant electric field. It is shown that the compatibility problem between the time derivative of the director field on the surface and in the bulk can be avoided.

Transient flow-driven distortion of a nematic liquid crystal in channel flow with dissipative weak planar anchoring

“…A dissipative weak anchoring condition has been used to study problems related to device switching, such as relaxation of director profiles and back flow (see, for example, [26,[29][30][31][32][33][34][35]), while Kléman and Pikin [36] formulated a dissipative weak anchoring condition in the context of Couette flow but only considered steady solutions. However, to the best of the authors' knowledge, surprisingly little research has thus far been carried out on the influence of dissipative weak anchoring on the problem treated in the present work, namely channel flow.…”

“…As described in Section I C, we take the boundary conditions for the director angle to be the so-called dissipative weak anchoring conditions (see, for example, [26,[29][30][31][32][33][34][35][36]) given by…”

“…The director-flow coupling timescale τ 3 also appears in the linear momentum equation 32and is the timescale on which changes in the velocity affect the director orientation and vice versa. The boundary director rotation timescale τ 4 appears in the dissipative weak anchoring conditions (33) and (34) and is the timescale of rotation of the director at the boundaries of the channel driven by splay elastic effects. In contrast to the bulk rotation timescale τ 1 , the boundary director rotation timescale τ 4 depends on the surface rotational viscosity γ S rather than the bulk rotational viscosity γ 1 .…”