A PHASE DIAGRAM OF SMECTOGEN-NON-SMECTOGEN BINARY MIXTURE: A PHOTON TRANSMISSION STUDY

The ultraviolet/visible photon transmission technique was applied to study the phase diagram of a mixture of 4-ethoxy-4′-(6-vinyloxyhexyloxyl) azobenzene (VE), a smectogen, and 4-hexoxy-3′-methyl-4′-(6-acryloyloxyhexyloxy) azobenzene (AH), which by itself exhibits no liquid crystalline behavior. It has been found that the N-Sm-A phase line terminates at either a tricritical point at about X_VE = 0.9, where X_VE is the weight percentage of VE in the binary mixture, or at least at a tricritical region 0.9 < X_VE < 1 within the experimental resolution. For X_VE = 1 the nematic phase region is not large enough to drive the transition second-order. It is found that the value of the critical exponent β for X_VE = 0.9 is consistent with the tricritical value.