Measurements of density and expansion coefficient for the nematic, lamellar smectic, and isotropic phase of micellar systems

Measurements of the density and expansion coefficient as a function of temperature are presented for two micellar systems, namely, decylammonium chloride/NH₄Cl/water, and cesium perfluorooctanoate/water. The measurements cover the lamellar smectic, the nematic, and the isotropic micellar solution. The measurements show that away from the phase transitions, the density decreases smoothly with increasing temperature. At the nematic‐to‐isotropic transition the density shows steplike features, indicating a change in the micellar structure at the transition, with denser packing of the amphiphiles in the micelles of the isotropic phase. A similar change is observed in the lamellar to nematic transition, however, the detailed behavior at this transition showed some dependence on the history of the sample. The expansion coefficients decrease at the transitions. Considerable pretransitional behavior is observed about the lamellar‐to‐nematic transition.