Hydrotropes: Solubilization of nonpolar compounds and modification of surfactant solutions

• Published in: Journal of molecular liquids 2023-01, Vol.370, p.120923, Article 120923
• Main Authors: Zakharova, Lucia Ya, Vasilieva, Elmira A., Mirgorodskaya, Alla B., Zakharov, Sergey V., Pavlov, Rais V., Kashapova, Nadezda E., Gaynanova, Gulnara A.
• Format: Article
• Language: English
• Subjects: Hydrotrope; Morphology; Self-assembly; Solubility; Surfactant
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2022.120923

[Display omitted] •The review covers hydrotrope research history and terminology.•Substantiated knowledge about hydrotropy mechanism is shown and current hypotheses are outlined.•Salting-in/out, hydrotrope aggregation, hydrotrope-solute complexes, co-solvent effects and water structure are discussed.•Hydrotrope interaction with surfactants and concomitant morphological transitions are covered.•Flexible stimuli-responsive self-organized hydrotrope-surfactant systems with tweakable aggregation behavior are covered. Control of size, charge, morphological characteristics, stability and functional activity of practically important compounds is of particular interest. Two classes of amphiphiles, hydrotropes and surfactants, attract wide attention in this respect, providing multiple increase in solubility of different families of practically relevant substrates, including drugs, catalysts, cosmetic and food ingredients, pesticides, etc. Despite the fact that hydrotropes are documented for a long time, little substantiated and generally accepted information is available on mechanism of their functioning and factors controlling their activity. This encourages researches to delve further into the fundamental problems of hydrotrope behavior and obtain additional experimental basis for the analysis. This review highlights the current state of scientific understanding of the role of hydrotropic compounds, summarizes some of key historical examples to explore and compare them with recent data. The types of hydrotropic additives and the mechanism of specific ion effect are discussed. Considerable attention is paid to the interaction between a hydrotrope and a non-polar solute. Separate section focuses on the combination of typical hydrotropes and surfactants, with solubility enhancement, morphological behavior and synergetic effects discussed.