Nanorheology of polymers, block copolymers, and complex fluids

The shear rheology of molecularly-thin films of fluids has been studied experimentally as it depends on sinusoidal frequency (linear response) or on sliding velocity (nonlinear response). Building upon previous identification of a solid-like state that is induced by confinement, we find the shear-induced transition to a sliding state in which the viscous dissipation is essentially velocity-independent. The mechanism appears to involve wall slip but Fourier transforms of the response reveal fluctuations, intrinsic to the sliding state, over all accessible frequencies. Other ongoing studies involve shear-induced changes in the fluorescence of confined fluorescent probes, shear dilatancy, and the contrast between the shear of simple nonpolar fluids, and block copolymers.