Dispersions of weakly charged thermoresponsive microgels at high densities.

Abstract

Poly-N-isopropylacrylamide-based microgels in aqueous dispersion exhibit a pronounced thermoresponse that allows to control their size and thus the volume fraction via temperature. Here, we study the phase behavior of aqueous dispersions of weakly charged microgels with small silica cores, employing different scattering techniques. From temperature- and concentration-dependent experiments in presence and absence of monovalent salt, we deduce phase diagrams. The central quantity to analyse the structure and thus the phase of the system is the static structure factor measured via small-angle scattering. As a reference, we also perform molecular dynamics computer simulations of systems of weakly charged particles, using a screened Coulomb (Yukawa) potential with a soft core to model the interactions between the microgels. For this model potential the phase diagram is known. By comparing structure factors determined by both experiment and simulation, we can assign the observed states of our soft model colloids to states in the Yukawa phase diagram.