Distribution of CoFe2O4 Nanoparticles Inside PNIPAM-Based Microgels of Different Cross-linker Distributions

The aim of this study is to tailor the inner structure of positively charged poly-(N-isopropylacrylamid-co-allylamine) (P(NIPAM-co-AA)) microgels for a better control of the distribution of negatively charged magnetic cobaltferrite (CoFe2O4@CA) nanoparticles (MNPs) within the microgels. Therefore, two different strategies are followed for the microgel synthesis: the (one pot) batch method which leads to a higher cross-linker density in the microgel core and the feeding method which compensates different reaction kinetics of the cross-linker and the monomers. The latter one is expected to result in a homogeneous cross-linker distribution. Information about the cross-linker distribution is indirectly gained by measuring the elastic modulus via indentation experiments with an atomic force microscope. While the batch method results in a higher elastic modulus in the center of the microgel indicating a core/shell structure, the feeding method leads to a constant elastic modulus over the whole microgel. The loa...