Swelling properties of colloidal poly(N-isopropylacrylamide) microgels in solution

The volume phase transition of colloidal poly(N-isopropylacrylamide) microgels with different cross-linker density has been investigated by dynamic light scattering and scanning electron microscopy. The surfactant-free emulsion polymerization provides spherical microgel particles with a very narrow size distribution. The amount of cross-linker has no significant influence on the final hydrodynamic radius in the swollen state at low temperature, but the uniform shape of the dried particles declines for cross-linker density below 1%. The volume change increases with decreasing connectivity of the gel which is due to topological constraints of the polymer network. While the critical temperature does not vary significantly, a change in the nature of the transition process from a continuous to a more discontinuous volume change was observed.