STRAIN-INDUCED ANCHORING TRANSITIONS

The orienting action of a mica surface on nematic liquid crystals is studied using a polarizing microscope. The experiments show that anchoring transitions can be induced by mechanical strain of the crystal surface. Characteristic patterns of phase boundaries are observed close to genuine or artificial inclusions on the mica surface where shear strains have all possible directions and a large range of amplitudes. In order to describe the observations, the thermodynamic potential as a function of the anchoring direction is expanded in a Fourier series reflecting the symmetry of the solid substrate. It is shown that both the well known adsorption-induced and the strain-induced anchoring transitions can be interpreted in terms of the same generic anchoring diagram in Fourier space.