Mechanical behavior of polystyrene microgels

Polystyrene microgels are nanometer-sized particles produced by polymerizat ion and crosslinking in microemulsion. As a result of their internal networ k structure, microgels have negligible intermolecular entanglement interact ions. This can have a profound effect on their rheology; it also leads to g lassy fracture resembling the behavior of low molecular weight, linear poly styrene. At higher frequencies, the mechanical response of microgels is qui te similar to that of linear polystyrene. Breakdown of time-temperature sup erpositioning occurs in the softening zone of the viscoelastic spectrum. In the glass transition region, the segmental relaxation function is broadene d and exhibits an enhanced dependence on temperature. The latter two effect s, due to the cross-linking of the microgels, are also seen in conventional , macroscopic networks.