Apparent effect of crosslinker concentration on structure and dynamics of polymeric microgels

The effect of the amount of crosslinker on the structure and dynamics of polysaccharide microgels synthesized in a surfactant solution was studied below and above volume phase transition. When the 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 found to be consistent with homogenously crosslinked microgels that displayed uniform reversible deswelling above the transition temperature. These microgels became more diffusive with temperature increase. At high crosslinker concentrations, microgels showed an unusual temperature dependence and signs of inhomogeneous crosslinking. In this regime, microgels grew in size and became less diffusive with increase in temperature. At intermediate crosslinker concentrations, microgels didn’t show significant dependence of their size on temperature except for a reproducible jump in size at the transition temperature. The apparent regimes are likely due to nonuniform crosslinker distribution in the polymer microgel, which leads to nonuniform density of microgel particles, especially at large concentrations of the crosslinker.