The shear rheology and flow behavior of highly entangled worm-like or polymer-like micelles is investigated. We measure the spatially resolved microstructure and concentration in the plane of flow for a viscoelastic solution of polymer-like micelles comprised of mass fraction 6.0% (volume fraction 6.6%) solution of 2:1 molar ratio cetylpyridinium chloride/sodium salicylate in 0.5 mol/L NaCl/D2O through the shear banding transition. Spatially resolved flow small-angleneutron scattering measurements in the velocity-velocity gradient (1-2) plane of flow establish the local microstructure, and scanning narrow-aperture flow ultrasmall-angle neutron scattering (SNAFUSANS) measurements indicate no flow-induced concentration gradients within measurement accuracy. These results show shear banding in this solution is not associated with an isotropic-nematic transition and are fundamentally important for validating models of shear-banding complex fluids.  A new experimental method is developed using simultaneous small angle neutron scattering (SANS) and nonlinear oscillatory shear rheometry to investigate the spatiotemporal microstructure evolution. We demonstrate the novelty of nonlinear oscillatory shear experimental methods to create and interrogate metastable material states. These include a precursory state to the shear banded condition as well as a disentangled, low viscosity state with an inhomogeneous supra-molecular microstructure flowing at high shear rates. This new experimental evidence provides insight into the complexities of the shear banding phenomenon often observed in sheared complex fluids and provides valuable data for quantitatively testing non-equilibrium theory.[1] Gurnon et al. ACS Macroletters, 2014 dx.doi.org/10.1021/mz5000152[2] Gurnon et al. Soft Matter, 2014, DOI: 10.1039/C3SM53113A

Spatially resolved concentration and segmental flow alignment in a shear-banding solution of polymer-like micelles in steady and oscillatory flow

248th National Meeting (2014)

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