Effect of solvents on the growth morphology of dl-alanine crystals

Abstract

Solvents have a significant effect on crystal morphology, particularly for polar organic crystals. However, the role played by solvents in enhancing or inhibiting crystal growth is still not completely understood. In this paper we investigated the morphologies of DL-alanine as a model of organic polar crystals grown from a mixture of aqueous solutions, with organic solvents such as isopropyl alcohol (IPA) and ethanol. DL-alanine crystals were grown from pure water for a large range of supersaturation in various solutions of water-isopropyl alcohol (IPA) and water–ethanol. The crystal morphology formed under different crystallization conditions was analyzed using an electron microscope and X-ray diffraction to determine the specific effects of each solvent. It was found that the quantity of the solvents in the crystallization solutions has a large influence on the crystal tip morphology, and on the crystal aspect ratio. Molecular dynamic simulations were used to determine the relative growth rates of different crystallographic planes and crystal morphology. A combination of experimental morphology and simulated morphology calculated using a theoretical method allows us to understand the role played by solvents on crystal growth and crystal morphologies of DL-alanine crystals.