Origin of de-swelling and dynamics of dense ionic microgel suspensions

A direct consequence of the finite compressibility of a swollen microgel is that it can shrink and deformin response to an external perturbation. As a result, concentrated suspensions of these particlesexhibit relaxation dynamics and rheological properties which can be very different with respect tothose of a hard sphere suspension or an emulsion.We study the reduction in size of ionic microgels inresponse to increasing number of particles to show that particle shrinkage originates primarily fromsteric compression, and that the effect of ion-induced de-swelling of the polymer network is negligible.With increasing particle concentration, the single particle dynamics switch from those typicalof a liquid to those of a super-cooled liquid and finally to those of a glass. However, the transitionsoccur at volume fractions much higher than those characterizing a hard sphere system. In the supercooledstate, the distribution of displacements is non-Gaussian and the dependence of the structuralrelaxation time on volume fraction is describable by a Volger-Fulcher-Tammann function.status: publishe