Morphology of crystals: Internal and external controlling factors

Abstract

Internal and external factors that influence the morphology of crystals are studied based on an inhomogeneous cell model. After discussing the reason of the failure of two basic assumptions, the equivalent wetting condition and the proportionality condition, the influence of the ambient phase is explicitly taken into account in terms of the surface characteristic scaling factor ${\mathit{C}}_{\mathit{l}}^{\mathrm{*}}$. In connection with the solid-fluid interfacial structure, which is commonly determined by the crystal and the ambient phase, ${\mathit{C}}_{\mathit{l}}^{\mathrm{*}}$ will provide the essential information concerning how the morphology of the crystals is affected. Within the framework of our formalism, internal and external factors controlling both equilibrium forms and growth forms of crystals are described separately. This offers a guideline for the modification of the habit of crystals. To describe the morphology of crystals, the periodic bond chain analysis can be used to determine the internal controlling factors, and the interfacial structure analysis, which is developed in this paper, can be used to determine the external controlling factors. These analyses are applied to predict the growth forms of n-paraffin crystals.