Pre-nucleation cluster formation upon ethyl acetate addition to an aqueous solution of an anionic hydrotrope

Abstract

Hydrotropes are used to solubilize poorly soluble solutes. Here the general features of the solution behaviour of the very common anionic hydrotrope sodium salicylate is investigated. With the use of density and scattering measurements, it is demonstrated that around the critical point neither pre-Ouzo structuring nor an Ouzo effect are present. By contrast, in a domain near the liquid-solid phase boundary, X-ray light and neutron scattering combined with a density excess determination prove the presence of dynamic aggregates. These aggregates are stabilized without any surfactants, but by selective solvation of ethyl acetate, reminiscent of stable liquid pre-nucleation aggregates. And most surprising: in water saturated by ethyl acetate (20% wt), sodium salicylate micellizes like a medium chain classical surfactant.