Experimental Determination of the Curvature-Induced Reduction in the Smectic A-Nematic Transition Poin

On the basis of an analogy between smectic A-nematic and superconductor-normal metal transitions, de Gennes has predicted that a twist or bend distortion should reduce T _AN with respect to that of a curvature-free sample. We report measurements of the reduction of T _AN on samples prepared in two different geometries. In the first, a magnetically induced twist distortion has been used to obtain preliminary data on 8 OCB and CBOOA samples. In the second, a wedge-shaped twisted nematic cell has been used to get quantitative data on the reduction of T _AN of CBOOA as a function of twist distortion.