Multiple Dynamic Regimes in Nanoparticle-Polymer Dispersions: A Combined Xpcs, Rheology, and DLS Study

We present a combined x-ray photon correlation spectroscopy (XPCS), dynamic light scattering (DLS) and bulk rheometry study of dynamical transitions in an anisotropic colloid-polymer suspension that exhibits multiple arrested states. The results provide insight to the mechanism for formation of repulsive glasses, attractive glasses, and networked gels through tunable short-range depletion attraction and long-range electrostatic repulsion. On addition of adsorbing polymer chains, we observe three distinct dynamical regimes:  a state with slow dynamics consisting of finite clusters, for which interparticle interactions are predominantly repulsive (RR); a second dynamical regime occurring above the saturation concentration of added polymer, in which small clusters of nanoparticles form via short-range depletion attraction (AR); and a third gel regime (GR) occurs above the overlap concentration in which dynamics of nanoclusters are independent of polymer chain length. The observed complex dynamical state diagram is primarily governed by the structural reorganization of nanoparticle cluster and polymer chains at the clay-nanoparticle surface and in the matrix, which in turn controls the dynamical and macro-rheological properties.