OBSERVATION OF PHASE-TRANSITION OF LIQUID-CRYSTALLINE POLYMERS BY ULTRASONIC METHOD - (HYDROXYPROPYL)CELLULOSE AND (N-HEXANOYLOXYPROPYL)CELLULOSE

Using ultrasonic measurements, phase transition behavior was examined for (hydroxypropyl)cellulose (HPC) in solution and (n-hexanoyloxypropyl)cellulose (HPC-C6) in bulk. For various kinds of HPC solutions, we observed a phase transition of Landau-Khalatnikov type in the variation of ultrasonic variables with polymer concentration. It is the first observation for lyotropic liquid crystalline polymer systems, so far as we know. The critical concentration varied with species of solvent and it became higher in the order of acetic acid, ethyl alcohol, dioxane, and water. For HPC-C6 in bulk, we found at least two kinds of phase transitions in the variation of ultrasonic variables with temperature. One of them is ascribable to the phase transition between liquid crystalline and isotropic phases (i.e., the phase transition of the first kind). Another phase transition may be one of the second kind, in the case in which one could not detect by conventional methods. Thus, it was found that ultrasonic method is very useful to study the phase transition behavior.