K-13-INDUCED DEFORMATIONS IN A NEMATIC LIQUID-CRYSTAL - EXPERIMENTAL TEST OF THE FIRST-ORDER THEORY

We consider predictions of the so-called ''first-order elastic theory' ' with non-zero elastic constant K-13 for a nematic cell with tilted m olecular orientation. The geometry has been suggested by Faetti to tes t the validity of different theoretical approaches to the problem of t he divergence K-13 elastic term. According to the first order elastic theory, in which only the first and second derivatives in the elastic free energy are retained, the K-13 term causes deformations at the cel l surface when a magnetic field is applied along the initial director n. These deformations can be observed in the measurements of the optic al phase retardation; the distinctive feature of the K-13 effect is no n-monotonous behavior of the phase retardation when the magnetic field increases. Despite a number of difficulties, the effect can be tested experimentally. We report experimental data on the behavior of the ne matic cell with a high pretilt angle and weak anchoring in a tilted ma gnetic field. These results show no significant deviation in the monot onous behavior of the phase retardation; therefore, the experiment doe s not confirm the predictions of the first-order theory when K-13 not equal 0.