Pressure Dependence of the Cholesteric Pitch Below and Above a Tricritical Point. Studies on Cholesteryl Myristate and Cholesteryl Oleyl Carbonate Near the Cholesteric-to-Smectic a Phase Transition

Publisher Website
Google Scholar
Abstract
In order to study the influence of a tricritical point on the untwisting of the cholesteric helix near the phase transition cholesteric-to-smectic A light reflection measurements were carried out with cholesteryl oleyl carbonate (COC) and cholesteryl myristate (CM) up to 4.5 kbar and 95°C. The untwisting of the helix can be observed by the divergence of the wavelength of maximum light reflection λR with pressure in the phase transition region. Whereas the existence of a tricritical point in the phase diagram of COC is already known experimental evidence could be given in the case of CM as well. A comparison of the pressure dependence of λR for COC as well as for CM below and above the tricritical point shows that the divergence of λR with pressure is only little altered by the change in phase transition order.