Structural, Kinetics, and Rheological Properties of Low Ionic Strength Dilute Solutions of a Dimeric (Gemini) Surfactant

The structural and dynamical properties of low ionic strength micellar solutions of a cationic gemini surfactant have been investigated by means of light scattering, T-jump, and rheological experiments. In the dilute regime, below the entanglement concentration, the surfactant molecules self-assemble into polydisperse micellar aggregates with size distribution extending up to ∼100 nm. Rheology and T-jump experiments show that the dynamical processes are speeded-up by the addition of salt. In particular the critical shear rate above which a shear thickening occurs increases with the salt content. Also the characteristic time for chain distribution equilibration after a thermal perturbation increases upon removal of salt to reach very large values in the salt-free case. This result supports the speculation given previously that the reversible scission could explain the strong dependence of the shear thickening behavior on thermal cycling.