Dilution-driven gel-sol-gel-sol transitions by the sequential evolution of surfactant micelles.

Here are described the dilution-driven gel-sol-gel-sol transitions in aromatic hydrotrope/zwitterionic surfactant bi-component aqueous mixtures. Long and entangled wormlike micelles (WLMs) of concentrated erucyl dimethyl amidopropyl betaine (EAPB) solutions sequentially transform into hexagonal liquid crystal phase (H1), highly concentrated spherical micelles (HCSMs), and finally hexagonal close packed micellar phase (HCP) upon gradual introducing an aromatic hydrotrope, sodium salicylate (NaSal). The HCP then successively converts into HCSMs, WLMs, and spherical micelles (SMs) upon further dilution with water, corresponding to a gel-sol-gel-sol transition. This dilution-induced HCSMs to WLMs transition results in an interesting thickening process, which is caused by a slow kinetic process, from the agglomeration and recombination of SMs to long and rigid WLMs via the intermediately formed rodlike micelles. In this work, the sustained adjustment of the competitive self-sorting and co-assembly between hydrotropes and surfactants by dilution was identified, benefitting the creation and application of WLMs fluids with switchable viscosity.