Characterisation of monodisperse poly(N-isopropylacrylamide) microgel particles

Poly(N-isopropylacrylamide) microgel particles prepared by emulsion polymer isation in the presence of anionic surfactant have been investigated in dif ferent media in the swollen and collapsed state by static and dynamic light scattering measurements. The microgel latex was found to be highly monodis perse. The particle scattering function fits well to the theoretical functi on of a sphere. The hydrodynamic diameter of the particles is significantly higher than the diameter calculated from the measured radius of gyration f or a sphere of constant density. The discrepancy was interpreted by a core/ shell structure of the microgel particles. If the particles are in the coll apsed state the two kinds of diameter coincide with each other, indicating that the microgel particles are compact spheres. In the globular state the gel still has 39% (w/w) water content. The particles bear a small surface c harge resulting in a long-range electrostatic interaction between the parti cles in an aqueous environment. It was observed for the first time that at a sufficiently low ionic strength the aqueous microgel particle system unde rgoes an ordered/disordered phase transition.