Calorimetric study of phase transitions in a liquid-crystal-based microemulsion.
A lyotropic inverse micelle phase composed of water, thermotropic liquid-crystal octylcyanobiphenyl (8CB), and surfactant (DDAB) was studied by using high-resolution calorimetry on several mixtures with 3%, 8%, and 15% micelle concentration. Calorimetric results show strong depression of the isotropic to nematic (I-N) phase-transition temperature. Broad heat-capacity anomalies show the existence of a wide coexistence range of isotropic, nematic, and smectic-A phases, which mimics the behavior of a new nearly stable thermodynamic phase. An observation of the rather sharp almost bulklike nematic to smectic-A (N-A) transition at low-temperatures indicates that our heat capacity results are consistent with the phase separation scenario in which significant number of micelles is expelled during I-N conversion leaving almost pure nematic phase at lower temperatures. It was found that micelles get almost completely remixed on heating the mixture back to the isotropic phase.
Jozef Stefan Institute, P.O. Box 3000, 1001 Ljubljana, Slovenia. zdravko.kutnjak@ijs.si
Zdravko
Z
Kutnjak
George
G
Cordoyiannis
George
G
Nounesis
Andrija
A
Lebar
Bostjan
B
Zalar
Slobodan
S
Zumer