Abstract
The modification of magnetic nanoparticles (MNPs) with a thermo-sensitive organic shell of poly(N-isopropylacrylamide) (PNIPAm) is reported. The surface of maghemite MNPs was modified in two steps: firstly, using a silane coupling agent and leaving vinyl pending groups on the MNPs surface; and secondly, grafting PNIPAm chains from the modified MNPs via a free radical polymerization. The results indicate that the method developed here for the modification of MNPs is an effective way of synthesizing thermo-responsive MNPs. They present a magnetic behavior due to the maghemite core and a thermal response based on a deswelling/swelling of their polymeric shell (PNIPAm).
Highlights
The preparation of non-toxic nanoparticles exhibiting colloidal stability in biological media and offering anchoring sites is currently a real challenge
Transmission Electron Microscopy (TEM) study of temperature-dependent aggregation As mentioned above, in order to have more conclusive evidence about the thermo-sensitive properties of magnetic nanoparticles (MNPs)-MEMO-poly(N-isopropyl acrylamide) (PNIPAm) dispersions and with the aim to support the results obtained by Dynamic Light Scattering (DLS), TEM images of the samples at different temperatures were taken after each experiment
The experimental procedure involved two synthetic steps: first, the covalent binding of a silane coupling agent (MEMO) to the surface of the MNPs; and secondly, the growing of PNIPAm chains by surface free radical polymerization achieving PINPAm-grafted MNPs. This approach is a simple and low cost methodology which can be used to obtain MNPs modified with an organic shell
Summary
The preparation of non-toxic nanoparticles exhibiting colloidal stability in biological media and offering anchoring sites is currently a real challenge. This observation could be explained considering that the use of higher monomer concentrations favours the formation of aggregates of modified MNPs due to secondary interactions (hydrophobic/hydrophilic), entanglement, or crosslinking between the polymer chains bounded to the MNPs. a complete characterization of the product MNPs-MEMO-PNIPAm with the lowest monomer ratio (1:6.5) was performed, which will be described .
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