A phase transition-like instability in static samples of twisted nematic liquid crystal when the surfaces induce tilted alignments

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Abstract
There has been, in recent years, a great interest in twisted orientation patterns in static samples of nematic liquid crystals (NLC). Here we investigate the behaviour of such structures when the limiting surfaces induce not planar alignment but homogeneously tilted alignment. It is shown that when the overall twist is equal to Π, there exists a critical value of the tilt angle at the surface where the expected twisted structure spontaneously transforms into a non-twisted orientation pattern. This transformation presents all the features of a phase transition, which can be either of first or of second order depending on the set of elastic constants of the material. Experimental confirmation has been obtained with MBBA