A comparison of linear and branched wormlike micelles using large amplitude oscillatory shear and orthogonal superposition rheology

Abstract

In this study, we present a comparative investigation of linear and branched wormlike micelles using two nonlinear rheological tools: orthogonal superposition rheology and large amplitude oscillatory shear (LAOS) rheology. The surfactants were a series of mixtures of octyl trimethyl ammonium bromide (C8TAB) and sodium oleate (NaOA). A transition from linear to branched wormlike micelles was obtained by either varying the relative ratio of NaOA to C8TAB at a fixed total surfactant concentration or by fixing the ratio of NaOA to C8TAB and varying the total surfactant concentration. Orthogonal superposition rheology imposes a small amplitude oscillatory shear strain over an orthogonally imposed shear flow to probe the effect of shear on the storage and loss modulus of the fluid. For both the linear and branched wormlike micelle solutions, the plateau modulus, the relaxation times, and the dynamic viscosity were all found to be sensitive to the strength of the orthogonally imposed shear rate. However, the non...