Construction of a highly viscoelastic anionic wormlike micellar solution by carboxylate gemini surfactant with a p-dibenzenediol spacer

The viscoelastic wormlike micellar solutions formed by the carboxylate gemini surfactant, O, O'-bis(sodium 2-dodecylcarboxylate)-p-dibenzenediol (referred to as C-12 phi C-2(12)), have been investigated by steady-state and dynamic frequency-sweep rheological techniques. Another system using its homologue, O, O'-bis(sodium 2-dodecylcarboxylate)-p-benzenediol (C-12 phi C(1)2), was also examined for comparison. Both C-12 phi C-2(12) and C-12 phi C-12 formed wormlike micelles without any additives. The C* corresponding to the onset of the semi-dilute regime was 48 mmol L-1 for C-12 phi C-2(12) and 160 mmol L-1 for C-12 phi C-12, respectively, showing the considerably high ability and efficiency of C-12 phi C-2(12) in forming wormlike micelles. The wormlike micelles started to entangle with each other at 60 mmol L-1 for C-12 phi C-2(12) and 300 mmol L-1 for C-12 phi C-12. The average length of the C-12 phi C-2(12) wormlike micelles was estimated to be about 1.0-1.9 mu m, significantly longer than the C-12 phi C-12 ones. The solution viscosity of C-12 phi C-2(12) at 200 mmol L-1 reached 613 Pa s, much higher than 24.2 Pa s for C-12 phi C-12 at 500 mmol L-1. The mechanisms of forming wormlike micelles in both cases were revealed by dynamic light scattering measurements. Differently from the normal micellar growth that C-12 phi C-12 displayed, C-12 phi C-2(12) was found to form large network-like aggregates at very low concentrations. These aggregates could more conveniently transform into threadlike (wormlike) micelles by continuously increasing the concentration of C-12 phi C-2(12), from which a new approach was realised for highly viscoelastic anionic wormlike micellar solutions.