Existence and nature of a smectic-A-hexatic-B-smectic-I point

The binary-mixture phase diagram of n-propyl-4'-n-decyloxybiphenyl-4- carboxylate [3(10)OBC] and n-butyl-4'-n-decyloxybiphenyl-4-carboxylate [4(10)OBC] has been investigated by optical microscopy, x-ray diffraction, and heat-capacity studies. Here 3(10)OBC and 4(10)OBC have the isotropic (I)-smectic-A (SmA)-hexatic-B and I-SmA-smectic-I (SmI) transition sequence, respectively. This binary-mixture study reveals two new features, namely, the existence of the hexatic-B-SmI transition and a SmA-hexatic-B-SmI point where the relevant three phases coexist.