Jump to main content
Jump to site search

Issue 35, 2017
Previous Article Next Article

Unifying hydrotropy under Gibbs phase rule

Author affiliations


The task of elucidating the mechanism of solubility enhancement using hydrotropes has been hampered by the wide variety of phase behaviour that hydrotropes can exhibit, encompassing near-ideal aqueous solution, self-association, micelle formation, and micro-emulsions. Instead of taking a field guide or encyclopedic approach to classify hydrotropes into different molecular classes, we take a rational approach aiming at constructing a unified theory of hydrotropy based upon the first principles of statistical thermodynamics. Achieving this aim can be facilitated by the two key concepts: (1) the Gibbs phase rule as the basis of classifying the hydrotropes in terms of the degrees of freedom and the number of variables to modulate the solvation free energy; (2) the Kirkwood–Buff integrals to quantify the interactions between the species and their relative contributions to the process of solubilization. We demonstrate that the application of the two key concepts can in principle be used to distinguish the different molecular scenarios at work under apparently similar solubility curves observed from experiments. In addition, a generalization of our previous approach to solutes beyond dilution reveals the unified mechanism of hydrotropy, driven by a strong solute–hydrotrope interaction which overcomes the apparent per-hydrotrope inefficiency due to hydrotrope self-clustering.

Graphical abstract: Unifying hydrotropy under Gibbs phase rule

Back to tab navigation

Publication details

The article was received on 03 Apr 2017, accepted on 25 Apr 2017 and first published on 11 May 2017

Article type: Perspective
DOI: 10.1039/C7CP02132A
Citation: Phys. Chem. Chem. Phys., 2017,19, 23597-23605
  •   Request permissions

    Unifying hydrotropy under Gibbs phase rule

    S. Shimizu and N. Matubayasi, Phys. Chem. Chem. Phys., 2017, 19, 23597
    DOI: 10.1039/C7CP02132A

Search articles by author