THE TEMPERATURE-COMPOSITION PHASE-DIAGRAM OF MONOMYRISTOLEIN IN WATER- EQUILIBRIUM AND METASTABILITY ASPECTS

The temperature-composition phase diagram of monomyristolein in water was constructed using x-ray diffraction. Low- and wide-angle diffracti on patterns were collected from samples of fixed hydration as a functi on of temperature in the heating direction on x-ray-sensitive film and /or image plates. The phases identified in the system include the lame llar crystalline phase, the lamellar liquid crystalline phase, the flu id isotropic phase, and two inverted cubic phases. Particular attentio n has been devoted to the issues of phase equilibrium and phase bounda ry verification. Cubic phase undercooling was examined by adjusting th e temperature of several samples in the cubic phase to a value where t he lamellar liquid crystalline phase represents equilibrium behavior. Cooling-induced structure and phase changes were monitored continuousl y over a 30-min period by recording low-angle diffraction patterns fro m the samples using a streak camera. The cubic-to-lamellar transition rate decreased with increasing sample hydration. Additionally, the tra nsition proceeded more rapidly at an incubation temperature of 25 degr ees C compared to that at 0 degrees C. A mechanism is proposed that ac counts for the hydration and temperature sensitivity of the phase tran sition under nonequilibrium conditions.