Action of hydrotropes and alkyl-hydrotropes

Hydrotropes are small molecule amphiphiles, having considerable industrial importance as agents for solubilization of hydrophobic substances in aqueous systems. The physico-chemical origin and mechanism of hydrotrope action has been a subject of academic debate and controversy for many years. One important issue is how close the solution physical chemistry of hydrotropes resembles that of common surfactants. This article seeks to improve the appreciation of this field by comparing thermodynamic, phase, spectroscopic and scattering studies of hydrotrope aqueous solutions. In addition, alkyl-hydrotropes are discussed, which represent a structural evolution from classic hydrotropes towards common surfactants, having solution properties more reminiscent of surfactants.