Effect of nonmesogenic impurities on the isotropic to smectic-A phase transition

Abstract

A phenomenological model is developed to describe the effect of nonmesogenic impurities on the isotropic to smectic-A phase transition. It is based on the coupling of the power expansions associated with the concentration variable and the symmetry-breaking order parameters. While this phase transition is first order in the mesogenic pure compound consisting of smectic-A phase, we show here that the order of this transition does not change when the nonmesogenic solute is added to a mesogenic pure compound. It is shown that the isotropic to smectic-A phase transition temperature is depressed and a two-phase region is formed due to the presence of impurities of the solutes. The available experimental data are consistent with our model.

Keywords:

• liquid crystals
• impurities
• metastable phases
• phase transition

Acknowledgements

The author thanks G.S. Iannacchione for providing his experimental data in numerical form. Special thanks go to the Alexander von Humboldt Foundation for equipment and a book grant.