Growth Rings in d-Sorbitol Spherulites: Connection to Concomitant Polymorphs and Growth Kinetics

Abstract

d-Sorbitol spherulites developed concentric rings in response to changes of crystallization temperature. Unlike extinction rings of polymer spherulites, these growth rings were linked to the concomitant crystallization of polymorphs (E and E‘) in temperature-dependent ratios. The growth rings provided a convenient way to measure the kinetics of crystal growth, similar to the use of tree rings in dendrochronology to determine the climatic effect on a tree's growth. The observed growth kinetics spanned 4 orders of magnitude and conformed approximately to the theory of interface-controlled growth parametrized with a viscosity-derived diffusion coefficient and thermodynamic driving force of crystallization. Near the glass transition temperature, however, the observed growth rate was faster than predicted, a discrepancy observed previously with other materials and attributed to the breakdown of the Stokes−Einstein relation between diffusion coefficient and viscosity. The same theory predicted a faster growth r...