Linear and nonlinear viscoelasticity of concentrated thermoresponsive microgel suspensions

We present an integrated experimental and theoretical study of the dynamics rheology self-crosslinked, slightly charged, temperature responsive soft poly(N-isopropylacrylamide) (pNIPAM) microgels over a wide range concentration spanning sharp change in particle size intermolecular interactions across lower critical solution (LCST). Dramatic, non-monotonic changes viscoelasticity are observed as function temperature, with distinct dependence dense fluid, glassy, soft-jammed regimes. Motivated by our observations, we formulate minimalistic model for single microgel interparticle interaction from purely repulsive to attractive upon heating. Using microscopic equilibrium time-dependent statistical mechanical theories, predictions quantitatively compared measurements shear modulus. Good agreement is found nonmonotonic behavior that originates consequence competition between reduced packing fraction increasing attractions. Testable made nonlinear rheological properties such yield stress strain. To knowledge, this first attempt understand unified manner dense, temperature-responsive suspensions temperatures concentrations.