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Anchoring

Anchoring is the preferred alignment of a liquid crystal near to a surface, for example the container walls. We investigate this by sandwiching the liquid crystal in a cell between two flat, planar, surfaces, and applying a strong orienting field near to (say) the left wall, as illustrated in the sketch below. The preferred molecular orientation will rotate across the cell, in a manner which depends on the bulk elastic constant K and on the surface anchoring coefficient W at the right wall. The anchoring strength is a crucial parameter in liquid crystal device design, and it may be dramatically altered by modifying the cell wall.

Typical results are shown in the graphs on the right. In the upper plot, we compare simulation results (blue) with a simple elastic theory (red). The key measurable quantity is the extrapolation length λ = K/W. In the lower plot, we compare with a simple density functional theory, which is a significant improvement over elastic theory in the wall region.

M P Allen, Mol Phys, 96, 1391 (1999)
D Andrienko, G Germano, M P Allen, Phys Rev E, 62, 6688 (2000)
D Andrienko, M P Allen, Phys Rev E, 65, 021704 (2002)
M T Downton, M P Allen, Europhys Lett, 65, 48 (2004)


Director profiles with orienting field on left of cell.