Manipulating of Crystal Morphology and Polymorph by Crystallization in Microemulsions

In this study, one microemulsion crystallization method, which could crystallize an organic compound with a specific structure and morphology, was developed by using glycine as a model compound. The solubility data of glycine in water/Triton X-100/n-pentanol/cyclohexane microemulsions at different temperatures (T = 20 and 35 degrees C) were measured to determine the initial crystallization supersaturation. Both antisolvent and cooling crystallization experiments in microemulsions with different compositions were conducted. Needle-like and polyhedral glycine crystals with millimeter-scale size were obtained. The effects of initial crystallization supersaturation, crystallization method, and microemulsion composition on the crystal morphology and polymorph were discussed. It was found that the crystal morphology was mainly controlled by the molar ratio of water molecules to surfactants (W = [water]: [Triton X-100]), and the oriented attachment of molecular clusters is the key factor for the formation of different crystal morphologies. Furthermore, all glycine crystals obtained belong to a-polymorph, which indicated that microemulsion crystallization could be used to control the structure of the crystals.