Independent control of polar and azimuthal anchoring

Abstract

Monte Carlo simulation, experiment, and continuum theory are used to examine the anchoring exhibited by a nematic liquid crystal at a patterned substrate comprising a periodic array of rectangles that, respectively, promote vertical and planar alignment. It is shown that the easy axis and effective anchoring energy promoted by such surfaces can be readily controlled by adjusting the design of the pattern. The calculations reveal rich behavior: for strong anchoring, as exhibited by the simulated system, for rectangle ratios 2 the nematic aligns in the direction of the long edge of the rectangles, the azimuthal anchoring coefficient changing with pattern shape. In weak anchoring scenarios, however, including our experimental systems, preferential anchoring is degenerate between the two rectangle diagonals. Bistability between diagonally aligned and edge-aligned arrangement is predicted for intermediate combinations of anchoring coefficient and system length scale.

Competition of lattice and basis for alignment of nematic liquid crystals

“…This is similar to the "bridging" behavior observed in rectangular patterned systems [5,35]. For the planar-on-vertical case [ Fig.…”

“…(7). As for other patterns [5,35], the director follows the surface pattern at ±d/2, while relaxing to a uniform orientation, equal to the average polar angle promoted by the surface far away from the boundaries.…”

“…The combination of Monte Carlo (MC) simulations and continuum theory has proven synergistic in previous studies [5,35] because the alignment induced by a particular pattern depends dramatically on the length scales present: MC probes alignment around patterns at the order of a few molecular lengths while continuum theory permits modeling up to device scales.…”

“…Additionally, if the polar angle depends on all of the coordinates θ = θ(x, y, z) and the azimuthal angle is constant in space φ = φ 0 [35], the bulk free energy may be rewritten as a quadratic form, and we introduced the dimensionless polar anchoring parameter…”

Liquid crystal alignment induced by micron-scale patterned surfaces

“…In this case, one must resort to the Landau-de Gennes Q-tensor theory in conjunction with numerical methods if defects are to be treated accurately [32][33][34]. In cases with sufficiently small patterns, molecular simulations have also been used to examine the anchoring effect and LC orientation near the patterns [11,35].…”