Aggregation, Gelation and Glass Transition in Mixed Suspension of Polystyrene Microsphere and Poly(N-isopropyl-acrylamide) Microgel

Poly(N-isopropylacrylamide) microgel is adsorbable to the polystyrene microsphere surface. The saturated adsorption concentration of microgel ($\Phi *_{\mathrm{MG}})$ is in a linear relationship with the given concentration of microsphere ($\Phi_{\mathrm{MS}})$. Depending on the concentration of microgel ($\Phi_{\mathrm{MG}})$ added into the suspension microspheres, the microgel can induce bridging ($\Phi _{\mathrm{MG}}$ \textless $\Phi *_{\mathrm{MG}})$, stabilizing ($\Phi _{\mathrm{MG}} = \Phi *_{\mathrm{MG}})$ and depletion ($\Phi _{\mathrm{MG}}$ \textgreater $\Phi *_{\mathrm{MG}})$ effect. With combination of various $\Phi_{\mathrm{MS}}$ and $\Phi _{\mathrm{MG}}$/$\Phi *_{\mathrm{MG}}$, different structures including stable solution, bridging and depletion cluster, bridging and depletion gel, attractive glass and repulsive glass, were obtained. The transitions between these states were investigated by rheology and microscopy. Two-step yielding behavior was observed in attractive glass, which was contributed from bridging bonds of microgels and caging effect of dense microspheres.