The polymerisation of oligo(ethylene glycol methyl ether) methacrylate from a multifunctional poly(ethylene imine) derived amide: a stabiliser for the synthesis and dispersion of magnetite nanoparticles

A facile synthetic route to poly(ethylene imine)-graft-poly(oligo(ethylene glycol methyl ether)) (PEI-graft-POEGMA) functionalised superparamagnetic magnetite nanoparticles is described. The polymerisation of OEGMA from a model molecular amide demonstrated the feasibility of POEGMA synthesis under mild ATRP conditions (20 °C in ethanol) albeit with low initiator efficiencies. DFT studies suggest that the amide functionality is intrinsically of lower activity than ester functional monomers and initiators for atom transfer polymerisation (ATRP) as a consequence of higher bond dissociation energies and bond dissociation free energies (BDFE). However these studies further highlighted that use of an appropriate solvent could reduce the free energy of dissociation thereby reducing the relative difference in BDFE between the ester and amide groups. A commercial branched PEI sample was functionalised by reaction with 2-bromo-2-methylpropanoyl bromide giving an amide macroinitiator suitable for the atom transfer radical polymerisation (ATRP) of oligo(ethylene glycol methyl ether) methacrylate. The resulting PEI-graft-POEGMA copolymers were characterised by SEC, FT-IR and 1H and 13C NMR spectroscopy. PEI-graft-POEGMA coated magnetite nanoparticles were synthesised by a basic aqueous co-precipitation method and were characterised by transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometry and dynamic light scattering. These copolymer coated magnetite nanoparticles were demonstrated to be effectively stabilised in an aqueous medium. Overall the particle sizes and magnetic and physical properties of the coated samples were similar to those of uncoated samples

Deterioration in effective thermal conductivity of aqueous magnetic nanofluids

Common heat transfer fluids have low thermal conductivities, which decrease their efficiency in many applications. On the other hand, solids have much higher thermal conductivity values. Previously, it was shown that the addition of different nanoparticles to various base fluids increases the thermal conductivity of the carrier fluid remarkably. However, there are limited studies that focus on the thermal conductivity of magnetic fluids. In this study, thermal conductivity of magnetic nanofluids composed of magnetite nanoparticles synthesized via co-precipitation and thermal decomposition methods is investigated. Results showed that the addition of magnetite nanoparticles decreased the thermal conductivity of water and ethylene glycol. This decrease was found to increase with increasing particle concentration and to be independent of the synthesis method, the type of surfactant, and the interfacial thermal resistance

A Bioinspired Coprecipitation Method for the Controlled Synthesis of Magnetite Nanoparticles

Nature often uses precursor phases for the controlled development of crystalline materials with well-defined morphologies and unusual properties. Mimicking such a strategy in in vitro model systems would potentially lead to the water-based, room-temperature synthesis of superior materials. In the case of magnetite (Fe₃O₄), which in biology generally is formed through a ferrihydrite precursor, such approaches have remained largely unexplored. Here we report on a simple protocol that involves the slow coprecipitation of Fe^III/Fe^II salts through ammonia diffusion, during which ferrihydrite precipitates first at low pH values and is converted to magnetite at high pH values. Direct coprecipitation often leads to small crystals with superparamagnetic properties. Conversely, in this approach, the crystallization kineticsand thereby the resulting crystal sizescan be controlled through the NH₃ influx and the Fe concentration, which results in single crystals with sizes well in the ferrimagnetic domain. Moreover, this strategy provides a convenient platform for the screening of organic additives as nucleation and growth controllers, which we demonstrate for the biologically derived M6A peptide