Viscoelastic properties of supramolecular gemini-like surfactant solutions in the absence of inorganic salts

Abstract

Exploration of novel wormlike micelle systems is important for both the theory and applications of surfactant self-assembly. A new anionic surfactant, sodium 2-phenoxyhexadecanoate (sodium Ph-C16), was synthesized in this work. This surfactant can self-assemble in solution to form wormlike micelles with the help of a bolaform salt, ethane-1,2-bis(trimethyl ammonium bromide) (N-2-N bromide), by removing inorganic salts. The resultant aqueous system was investigated using rheological measurements, freeze-fractured-TEM and 2D NOESY ¹H NMR experiments. A supramolecular gemini-like structure constructed from electrostatic interactions was a prerequisite for the wormlike micelle formation. The zero shear viscosity (η₀) of the system had a very strong dependence on the surfactant concentration with a scaling exponent of 16.8 in the semi-dilute region, which is attributed to the extremely strong electrostatic attraction between the surface-active anions and bolaform cations. These results are beneficial for understanding anionic wormlike micelles in the absence of inorganic salts.