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

Abstract

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 (CoFe 2 O 4 @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 loading with MNPs and their distribution are studied with transmission electron microscopy (TEM). The TEM images show a large difference in the MNP distribution which is correlated to the cross-linker distribution of both types of microgels. The batch method microgel has a low MNP concentration in the core. The feeding method microgel shows a much more homogeneous distribution of MNPs across the microgel. The latter one also shows a stronger charge reversal which is a hint for a higher loading of the feeding method microgel. Dynamic light scattering and electrophoretic mobility measurements demonstrate that for both types of microgels, the temperature sensitivity is preserved after loading with MNPs.

Review on the advancements of magnetic gels: towards multifunctional magnetic liposome-hydrogel composites for biomedical applications

“…Concerning the fabrication of magnetic gels to attain the desired properties, several strategies have been developed. The main methods can be classified as blending method [176], grafting method [177], in situ precipitation [178], and swelling method [179]. These methods can be aggregated in polymer-first (in situ precipitation and swelling method) and particle-first (blending and grafting methods) strategies [35].…”

“…(B) TEM image of PNIPAM magnetic microgels, with the core microgel prepared from the batch method (left) and feeding method (right). Adapted from reference [179] with permission from American Chemical Society, 2020. (C) Schematic representation of the methods for preparation of magnetic gels: (I) grafting method; (II) blending method; (III) in situ precipitation method and (IV) swelling method.…”

Pathways and challenges towards a complete characterization of microgels

“…Most of the recent advances in nanoscale characterization have been targeted toward simple, radially isotropic microgels. Here, we would like to point toward not only experimentally more challenging but also highly exciting applications of nanoscale imaging, such as functional microgels, for example, microgels with certain comonomers, polymer-nanoparticle hybrids, Janus particles, or microgel-based colloidal molecules [98][99][100][101] . A comprehensive discussion of functional microgels would be beyond the scope of this paper and can be found elsewhere 12 .…”

Effect of heterogeneous and homogeneous polymerisation on the structure of pNIPAm nanogels

“…The increase in electrophoretic mobility of NG1 with temperature can be associated with an increase in charge density due to the expulsion of water from the polymer matrix and rearrangement of the charged initiator residues towards the surface. [51][52][53][54][55] On the contrary, for NG2, a sharp increase in electrophoretic mobility at VPTT corresponds to the formation of stabilised positively charged aggregated particles, since aggregation of NG2 above VPTT is observed by DLS and UV-Vis at this concentration (Fig. 2a and b).…”