Shear thinning and orientational ordering of wormlike micelles -: art. no. 017803

Shear thinning and orientation of cylindrical surfactant and block copolymer micelles was investigated by rheo-SANS (small-angle neutron scattering) experiments. Shear thinning and orientation occur for shear rates (gamma) ocer dot tau(dis)much greater than1, where tau(dis) is the disentanglement time of the micelles. Micelles align in the flow direction with an orientational distribution that can be well described by an Onsager-type distribution function. Over nearly the whole range of concentrations and for all cylindrical micelles investigated, the shear viscosity eta follows a simple etasimilar toe(-aS) behavior as a function of the orientational order parameter S with the same prefactor a.