Wormlike Micelles Formed by Sodium Erucate in the Presence of a Tetraalkylammonium Hydrotrope

Anionic wormlike micelles, particularly those formed by long-chain carboxylate surfactants, are relatively less documented though their cationic or zwitterionic counterparts are frequently reported. In this study, the wormlike micelles of sodium erucate (NaOEr), a C22-tailed anionic surfactant with a monounsaturated tail, in the presence of a tetraalkylammonium hydrotrope were investigated for the first time. The different effects of two hydrotropes, benzyl trimethyl ammonium bromide (BTAB) and tetramethyl ammonium bromide (TMAB), on the phase behavior and rheological behaviors were compared, and the influences of surfactant concentration and temperature on the rheological properties of NaOEr solutions were also examined. Both organic salts can lower the Krafft temperature of NaOEr solutions and thus improve its water solubility, but BTAB can make T(K) drop. more sharply. At a fixed NaOEr concentration, less BTAB is demanded to induce the formation of viscoelastic solution and to obtain the maximum viscosity of NaOEr solution; at a constant salt concentration, with increasing NaOEr content, the NaOEr-BTAB system shows a larger zero-shear viscosity (eta(0)), relaxation time, and plateau modulus but lower overlapping concentration than those of the NaOEr-TMAB system. The occurrence of maximum eta(0) with increasing salt content for the NaOEr-BTAB system results from the formation of vesicles and L(3) phases, which were verified by cryo-TEM observations. eta(0) shows an exponential decrease with increasing temperature; nevertheless it still remains above 10(3) mPa.s even at 90 degrees C.