Non-ionic polar small molecules induced transition from elastic hydrogel via viscoelastic wormlike micelles to spherical micelles in zwitterionic surfactant systems

Abstract

• A C18-tailed zwitterionic surfactant supramolecular hydrogel is constructed with OHSB and NaSal. • The non-ionic polar small molecules, TPA1, could control the microstructure and viscoelasticity of zwitterionic hydrogel. • Rheological measurement shows transition from Elastic Hydrogel via Viscoelastic Wormlike Micelles to Spherical micelles. • The microstructure of the system was analyzed by cryo-TEM and cryo-SEM. • The construction and transition mechanism were proposed, stating the detailed controlling process clearly. Supramolecular assembly determines the formation and transformation of soft materials. So far, the construction and transformation of conventional (<C20) zwitterionic surfactant elastic hydrogel have been a challenging and vital issue. In this work, a C18-tailed zwitterionic surfactant supramolecular hydrogel is constructed with N -octadecyl- N , N -dimethyl-3-ammonio-2-hydroxy-1-propane-sulfonate (OHSB) and sodium salicylate (NaSal). The N , N ,2,2-tetramethyl-1, 3-propanediamine (TPA1), as the non-ionic polar small molecules, were chosen to control the microstructure and macro-viscoelasticity of zwitterionic surfactant supramolecular hydrogel. With the addition of TPA1, the rheological properties and microstructural images of the OHSB/NaSal system show that the microstructure has changed from elastic hydrogels via viscoelastic wormlike micelles (WLMs) to spherical micelles. With the N , N , N’ , N’ -tetramethyl-1,3-propanediamine (TPA2), the isomer of TPA1, is added into OHSB/NaSal system in the same concentration, the difference in rheology and microstructure indirectly indicates the influence of hydrogen bonding on self-assembly. By systematically varying components, insight into the intermolecular interaction between OHSB, NaSal, and TPA1 and its effect on the microstructure during aggregation and transition are gained by the complementary use of 1 H NMR, rheological property, cryo-SEM, cryo-TEM, and DLS. We expect it to be a good model for conventional zwitterionic surfactant supramolecular hydrogel and a new method for controlling the internal nanostructure of micelles, which is helpful to understand the construction and finely tune of conventional zwitterionic surfactant supramolecular hydrogel and widen their applications.