Pressure induced tricritical point at the cholesteric-smectic-A phase transition

摘要

A phenomenological theory is presented to describe the pressure effect on the cholesteric to smectic-A phase transition. The problem of first or second order character of the cholesteric to smectic-A phase transition is explored by means of the variation of the pressure. The possibility of the tricritical point at the cholesteric to smectic-A transition line is discussed in a phenomenological way. It is shown that with a particular value of the pressure, the first order cholesteric to smectic-A transition becomes second order at a pressure induced tricritical point. The obtained topologies of the pressure-temperature phase diagram qualitatively agree with experimental results.