Generation of nanometer-scale crystals of hydrophobic compound from aqueous solution

Abstract

A hydrophobic compound dissolves very slightly in an aqueous solution. As an application of such dilute solubility, the concept for making nanometer-scale crystals of lauric acid from the aqueous ethanol solution was suggested. There are two different dilute solubilities in the aqueous phase. One thing is defined as the solubility of solid lauric acid; another is defined as the mutual solubility of liquid–liquid equilibrium between aqueous phase and oil phase. Two possible processes for crystallizing lauric acid were shown according to two different solubility curves. One process is direct crystallization of lauric acid; another process is indirect crystallization of lauric acid after emulsification. The crystals formed by two processes were experimentally observed, and then the size of crystals was analyzed by dynamic light scattering (DLS). The crystals formed through both emulsification and crystallization processes were 500 nm in size. The crystals formed through direct crystallization process ranged from 30 to 100 nm in size. The size of the latter crystals was a function of ethanol mole fraction in aqueous phase and cooling temperature. The modified Gibbs–Thomson equation was examined to correlate the crystal-nuclei size of the wide range.