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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.
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.