Physical properties of aromatic hydrocarbons: V. The solidification behavior of 1:2 diphenylbenzene

Abstract

The crystallization behavior of purified 1:2 diphenylbenzene has been studied over approximately six orders of magnitude in growth rate and 75°C of undercooling. Crystallization rates range from 1.81 × 10 -6 cm sec -1 at 55.1°C to 3.60 × 10 -3 cm sec -1 at 39°C (where the rate passes through a maximum value), down to 3.40 × 10 -9 cm sec -1 at -19.1°C, the lowest temperature studied. The growth rate varies smoothly with temperature, but cannot be adequately described by the classical Fisher-Turnbull model for crystallization kinetics. The logarithm of the product of the growth rate and the viscosity varies non-linearly with the undercooling cooling expressed as ( TΔ T) -1. When self-diffusion data are used in the analysis in place of the viscosity results, an almost linear dependence was noted. However, it was also necessary to modify the transport term of the rate equation since the classical Arrhenius form overestimates the contribution of the interfacial transport term to the growth rate. A kinetic limit at small undercooling, in excess of 1°C, and other morphological and kinetic evidence support a surface nucleation growth mechanism. The crystalline phase exhibits a faceted interface at all temperatures in keeping with Jackson's model for materials possessing large entropies of fusion. Parameters pertinent to the crystalline and glassy condition of 1:2 DPB are discussed and compared with other materials. Factors responsible for the disagreement between theory and experiment are discussed.