We present an experimental and theoretical study of the pincement phenomenon-transformation of a wall associated with the Fréedericksz transition into a pair of disclination lines. We measure the velocity of the boundary (front) between the two states as a function of the voltage. Experimental results are recovered by numerical simulations based on the nematic tensor order parameter, which also reveal the detailed three-dimensional structure of the front. By introducing reduced models we obtain approximate expressions for the two-state coexistence voltage and the front velocity. We find a bifurcation scenario incorporating a pair of saddle nodes at which the wall and disclination solutions appear or disappear.

A thermoreversible (physical) gel consisting of a nematic liquid crystal mixed with a small quantity of a chiral organogelator is investigated in the planar configuration. The response of the system to an external electric field reveals multistability within a small hysteresis. The relaxation of the liquid crystal under this field is characterized by two different time scales: a fast one that is connected to the tilt of the director field, and a slow one that describes the reorientation of the chiral structure. In the first case, the relaxation is nonexponential and can be described by a Kohlrausch-Williams-Watts law with a stretching parameter of 0.5.