Effect of molecular ordering on the pressure behaviour of the nematic-isotropic transition in binary reentrant nematic mixtures

Abstract

Binary mixtures of N-p-cyanobenzylidene-p'-octyloxyaniline (CBOOA) and 4'-n-octyloxy-4-cyanobiphenyl (8 OCB) exhibit the reentrant nematic phase at atmospheric pressure over a certain range of composition. We have studied the effect of pressure on the nematic-isotropic transition of these mixtures. It is found that a plot of dT/dP versus the molar concentration of CBOOA shows two minima which occur almost exactly at the same concentrations at which the reentrant nematic phase makes its appearance at atmospheric pressure. These results indicate that the structural changes which accompany the formation of the reentrant nematic phase are strong enough to affect the pressure behaviour of even the nematic-isotropic transition.