Identification of Polar Plots of Crystal Dissolution Rates Using Hot-Stage Microscopy

Polar plots are the representations of the 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,¹ whereas the morphologies of dissolving crystals are known to have no steady-states.²Here 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 crystal towards faceted morphology involves disappearance of slow-dissolving faces, which also causes vanishing of curvatures from 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 sub-saturations.         

References:

 (1)       Singh, M. R.; Verma, P.; Tung, H.-H.; Bordawekar, S.; Ramkrishna, D., Screening Crystal Morphologies from Crystal Structure. Crystal Growth & Design 2012, 13, (4), 1390-1396.

(2)        Snyder, R. C.; Doherty, M. F., Faceted crystal shape evolution during dissolution or growth. AIChE journal 2007, 53, (5), 1337-1348.