Phase behavior of PNiPAM-PEG microgel suspensions

Cross-linked Poly($N$-isopropylacrylamide) (PNiPAM) microgels have been a focus of research in the last decade, with particular interest in the swelling and de-swelling response of particles with temperature, ionic strength and pH. In this work we investigate the phase behavior of PNiPAM microgels cross-linked with Poly(ethylene glycol) (PEG) in aqueous suspensions. We characterize this class of microgels at low concentrations employing light scattering techniques and find that in contrast with other cross-linkers, the properties of PEG at different temperatures result in an unusual intra-particle configuration that guarantees a repulsive interaction between particles throughout the spanned temperature range. We study the dynamic and mechanical properties of PNiPAM-PEG microgel suspensions as a function of temperature at a generalized volume fraction of \textit{$\zeta $} = n$_{p}$ V$_{0}$ = 1.5, with n$_{p}$ the particle number density and V$_{0}$ the volume of a particle at low concentrations. Interestingly, despite we keep \textit{$\zeta $ }constant, we find dramatic changes in behavior with temperature. As a result, the phase behavior of these systems also changes; it exhibits analogies and mark differences with hard sphere behavior.