Studying the Effect of Crosslinker Concentration on Structure, Dynamics, and Volume Phase Transition of Microgels.

The effect crosslinker concentration on the structure and dynamics of polysaccharide microgels synthesized with surfactant was studied below and above volume phase transition. When relative amount of crosslinker was varied by a factor of a hundred, three apparent behavioral regimes emerged from static and dynamic light scattering measurements. At low crosslinker concentrations, microgel behavior was consistent with homogenously crosslinked microgels that displayed uniform deswelling above the transition temperature. The microgels became denser and more diffusive with temperature increase. At high crosslinker concentrations, microgels had an unusual temperature dependence and signs of inhomogeneous crosslinking. In this regime, microgels grew in size and became less dense and less diffusive with temperature increase. At intermediate crosslinker, microgels’ size and density didn’t significantly depend on a solution temperature. The apparent regimes are likely due to nonuniform crosslinker distribution in the microgel, which leads to a nonuniform density of microgel particles, especially at large crosslinker concentrations. Light scattering data was analyzed with Flory-Rehner model and compared to predictions for various microgel architectures.