Evidence of a first-order smectic-A–smectic-C* transition and its approach to tricritical behavior

Abstract

Evidence of a first-order smectic-A–smectic-C* (SmA-SmC*) transition is presented. Detailed x-ray studies on 4-(3-methyl-2-chloropentanoyloxy)4’-heptyloxybiphenyl show that the SmA-SmC* transition in this material is characterized by a discontinuous jump in the layer spacing (and hence in the tilt angle) and by a narrow two-phase region in which the density modulations due to the smectic-A and the smectic-C* phases coexist. Addition of a second compound drives the SmA-SmC* transition towards second order.