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Light scattering study of spherical poly(N-isopropylacrylamide) microgels

Abstract Nearly monodisperse spherical microgel particles of poly(N-isopropylacrylamide) (PNIPAM) were prepared by emulsion polymerization in water. The volume phase transition of the microgel particles was studied by static and dynamic laser light scattering (LLS) in terms of the radius of gyration (Rg ) and hydrodynamic radius (R h). The phase transition temperature of the microgel ∼33.0°C, similar to that of individual PNIPAM chains in water. The temperature independence of R g/Rh(∼0.78 ± 0.03) shows that in both the swollen and collapsed states the microgels are uniform particles behaving as hydrodynamically equivalent spheres. About 94% of the water inside the microgel network is driven out during the phase transition. The volume change of the microgel particles is continuous, in contrast to the discontinuous volume change observed in some bulk PNIPAM gels. The microgel particles are thermodynamically stable even at their collapsing limit. The behavior of microgel particles is compared to that of ind...