Large amplitude oscillatory shear rheo-NMR velocimetry

Abstract

Complex fluids display flow heterogeneities and a variety of nonlinearities under large amplitude oscillatory shear (LAOS). LAOS has developed as a means of characterizing nonlinear fluid rheology. In this study, the spatial velocity distribution during LAOS is measured by rheo-nuclear magnetic resonance (Rheo-NMR) velocimetry. Rheo-NMR is frequently used to measure responses of complex fluids to steady shear deformations by imaging local velocity across a fluid gap noninvasively. Rheo-NMR analysis of oscillatory flow has been more limited due to hardware limitations. Recently developed Rheo-NMR equipment makes LAOS Rheo-NMR possible. LAOS Rheo-NMR provides measurement of spatial velocity profiles as a function of oscillatory period, providing time dependent spatially resolved local velocity time series, which show distinct features dependent on material response.