Abstract
Binary mixtures of two compounds with phase sequences isotropic (I)–chiral-nematic (N)–chiral-smectic-C () and I–N–smectic-A (A)– have been investigated. Spontaneous-polarization and tilt-angle measurements near the A- transition indicate a mean-field-like to tricritical crossover behavior near the N-A- point of the phase diagram, the critical exponent β varying continuously from values near 0.5 to almost 0.25. The heat capacity has also been measured with a high-resolution ac calorimetric technique at the A- and N-A transitions of three mixtures. It is found that the A- transition is well described by an extended mean-field model. The fits show that, in accordance with polarization and tilt-angle measurements, the transition evolves from a second-order regime towards tricriticality as the A range decreases. Based on these results and other analogous studies published by other authors, some considerations about the material requirements necessary to obtain first-order A- transitions are briefly discussed.
- Received 8 March 1993
DOI:https://doi.org/10.1103/PhysRevE.48.1970
©1993 American Physical Society