Understanding the Dissolution Mechanism of Hydrophobic Dyes through Statistical Thermodynamics

Abstract

Hydrophobic dyes are used in water with solubilizers. Hydrotrope is a solubilizer of low molecular weight, weakly amphiphilic organics. and is known to promote solubilization of drugs, dyes, and pigments. One of most famous hydrotropes, urea, serves as an efficient solubilizing agent for dyes. In this study, in order to elucidate the molecularlevel mechanisms responsible for urea's effectiveness as a solubilizer, we apply a statistical thermodynamics approach rooted in the Kirkwood-Buff theory of solutions. Our findings demonstrate two key insights: (i) in contrast to the traditional notion of " water structure disruption, " the impact of urea on dye hydration has a relatively minor role in the solubilization process; (ii) the primary driving force for solubilization arises from the accumulation of urea molecules surrounding hydrophobic dye molecules.