(79f) Large Amplitude Oscillatory (micro-)Rheology

A microstructural understanding of the origin of the large-amplitude rheological response of common (e.g. colloidal dispersions and polymer melts) and exotic (e.g. slug mucus) materials, as well as the behavior of various constitutive models when forced in the same fashion, is an on-going challenge.  We have conducted a detailed study of the response to large amplitude oscillatory flows (LAOF) from a micro mechanical perspective -- the microrheology of colloidal dispersions. The suspension microstructure, satisfying the Smoluchowski equation, is decomposed into temporal normal modes which are coupled together by the imposed flow. The solution for these coupled structure functions provides considerable insight into the physical processes involved in large amplitude flows, in particular, the competition between hydrodynamic and thermal forces. We compare the linear and non-linear response for suspensions with and without hydrodynamic interactions and contrast colloidal probes driven by an imposed force and an imposed velocity.  We also show how the microrheological behavior connects to macrorheological LAOS.