Measurement of Polar Plots of Crystal Dissolution Rates Using Hot-Stage Microscopy. Some Further Insights into Dissolution Morphologies

Abstract

Polar plots are the representations of anisotropic surface properties such as surface energies and growth rates of crystalline materials. The steady-state morphologies of growing crystals are usually obtained from Wulff constructions on the polar plots of growth rates, whereas the morphologies of dissolving crystals are known to have no steady states. Here we show that the dissolving crystal can attain steady-state morphologies under certain conditions. The Wulff construction on the polar plots of dissolution time (or slowness) can be used to identify such steady-state morphologies. It is shown that the dissolving crystal can attain faceted morphology composed of fast dissolving faces. The evolution of dissolving crystals toward faceted morphology involves disappearance of slow-dissolving faces, which also causes vanishing of curvatures from the crystal surface. This article presents a method to experimentally determine polar plots from the dynamic images of crystals obtained from hot-stage microscopy. The method relies on the solution of the characteristics for crystal dissolution. The methodology is demonstrated to obtain polar plots of succinic acid at different subsaturations.