Role of Solvent and External Growth Environments to Determine Growth Morphology of Molecular Crystals

Abstract

We report a computational method to investigate the mechanism through which the solvent interacts with the crystal surfaces during the crystal growth process. We have considered the role of the internal, crystal-solution interfacial structure and external growth environments affecting crystal growth to predict the growth morphology by calculating relative growth rate of different crystal faces. The interfacial structure and bonding energies of solute and solvent molecules of faces having different crystallographic orientations are obtained using periodic first-principles density functional method. The effects of molecular orientation of growth units and surface relaxation of the habit faces have also been considered in order to identify the adsorption of rate-determining molecules to different faces of crystals for their growth. On the basis of the analysis of interfacial structure and external growth environment, the expression for growth rates relating the level of supersaturation, temperature, solubility, bonding energies of solute–surface, solvent–surface, and the rate of growth has been derived. The method is applied to study growth morphology of two molecular crystals, namely, urea and β-succinic acid crystals from vapor and different solvents. The results obtained from calculations match well with the corresponding available experimental data. The remarkable agreement between the predicted growth shapes and the corresponding experimental results allow us to understand the role played by solvents and external growth factors on growth morphologies of molecular crystals.