SURFACE-INDUCED NEMATIC ORDER VARIATION - INTRINSIC ANCHORING AND SUBSURFACE DIRECTOR DEFORMATIONS

The nematic orientation close to a solid substrate is investigated by means of a Landau-de Gennes phenomenological model. We show that a spa tial variation of the scalar order parameter induces a subsurface vari ation of the average molecular orientation and an intrinsic contributi on to the anchoring when the splay and bend elastic constants are diff erent from the twist elastic constant. A quasi-splay-bend elastic cons tant is deduced by comparing the surface term proportional to the firs t derivative of the tilt angle with the one proposed long ago by Nehri ng and Saupe [J. Chem, Phys. 54, 337 (1971); 56, 5527 (1972)], The eff ective anchoring being a combination of the external contribution orig inating from the interaction with the substrate and the intrinsic anch oring energy resulting from the spatial variation of the scalar order parameter is analyzed. Matching elastic and magnetic effects on a nema tic slab, the corresponding effective extrapolation lengths are estima ted.