Beschreibung:
Zusammenfassung: The aim of this thesis was a systematic characterisation of the influence of cross-link density on physical properties of polystyrene(PS)-microgels. This study focused on the inner structure of the particles and their softness as well as on their structural and dynamic properties in comparison to homogeneous hard spheres (HS). In addition, the influence of cross-link density on polymer induced aggregation of dilute colloidal suspensions was investigated.Previous work of this group showed that 1:10- (i.e. one cross-link per ten styrene units) and 1:50-cross-linked PS-microgels can be described as effective HS. This outlines the major difference between these particles and the commonly used poly(N-isopropylacrylamide)(PNIPAM)-microgels. In this study the cross-link densities and particle radii were varied (1:10-100, 150 – 280 nm). We showed that particles of a cross-link density up to 1:50 can be described as homogeneous spheres, independent of their overall size. Only weaker cross-linked particles showed a small radial decay of cross-link density with which could be controlled via the reaction conditions. This decay was much smaller than the one usually observed for PNIPAM-microgels. Furthermore rheological measurements revealed larger hardness-parameters than usually reported for PNIPAM.