MICROGELS - COLLOIDAL MODELS FOR THE CROSS-LINKED STATE

This article describes the synthesis of various types of microgels with different cross-linking topologies. The swelling data of the standard systems can be fitted with non-affine theories of rubber elasticity. Light scattering shows the existence of long-range swelling heterogeneities. The dynamic mechanical behaviour shows some peculiarities, e.g. small spherical microgels show viscous flow. Besides statistically cross-linked systems, critically cross-linked as well as macroporous systems can be made. The critical systems exhibit a fractal structure scaling which depends on synthetic conditions. This dependence agrees well with the different dynamic percolation theories. On the other hand, no clear relation between structure scaling and the observed dynamic behaviour can be found. A qualitative scheme which explains various effects observed during cross-linking of microgels is presented.