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 $\dot{\gamma }{\tau }_{\mathrm{d}\mathrm{i}\mathrm{s}}\gg 1$, where ${\tau }_{\mathrm{d}\mathrm{i}\mathrm{s}}$ 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 $\eta \sim e^{-aS}$ behavior as a function of the orientational order parameter $S$ with the same prefactor $a$.

• Received 16 December 2003

DOI:https://doi.org/10.1103/PhysRevLett.94.017803