Phase Behavior of Thermally Responsive Microgel Colloids

The phase behavior of poly-$N$-isopropylacrylamide (PNIPAM) nanoparticles dispersed in water is investigated using a thermodynamic perturbation theory combined with light-scattering and spectrometer measurements. It is shown how the volume transition of PNIPAM particles affects the interaction potential and determines a novel phase diagram that has not been observed in conventional colloids. Because both particle size and attractive potential depend on temperature, PNIPAM aqueous dispersion exhibits phase transitions at a fixed particle number density by either increasing or decreasing temperature.