A Calorimetric Measurement of Phase Transformation Kinetics in Solid Octaphenylcyclotetrasiloxane: Evidence for Nucleation as the Rate Determining Process

Abstract

The kinetics of transformation from the metastable (at high temperature) solid 3-phase of octaphenylcyclotetrasiloxane to the stable 2-phase have been measured by a calorimetric technique. The results of the kinetic study and several related experiments are consistent with the view that nucleation is the rate determining process. Transformation time constants for large and small crystallites were found; the temperature dependence of each is in accord with the Turnbull-Fisher nucleation theory. From that theory γ, the interfacial energy between the 3- and 2-phases, has been found to be -3 ergs/cm², an order of magnitude smaller than that for typical liquid-solid interfaces. A study of the dependence of the transformation kinetics on crystallite size suggests that the phase change is surface nucleated.

Key Words:

• phase transitions
• phase transformation kinetics
• calorimetry
• nucleation
• solid-solid transitions