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Magnetic and rheological properties of poly(ethylene oxide)/iron oxide nanocomposite hydrogels synthesized using a one-step γ- radiolytic method

Magnetic polymer gels are a new promising class of nanocomposite gels with numerous potential applications as effective absorbents of toxic ions in water, in soft actuators such as artificial muscles, in tissue engineering, drug delivery, hyperthermia applications, etc. In this work, the magnetic and rheological properties of radiologically synthesized magnetic PEO/iron oxide hydrogels were systematically investigated. Magnetic PEO/iron oxide nanocomposite hydrogels were for the first time synthesized by a one-step γ-irradiation method starting from poly(ethylene oxide) (PEO) and iron(III) suspensions, followed by the simultaneous crosslinking of PEO chains and reduction of Fe(III) precursor. Magnetic hydrogels with embedded magnetite nanoparticles were obtained with 2-propanol and at high doses, as confirmed by XRD, SEM, TEM and Mössbauer spectroscopy. Rheological measurements confirmed the formation of a well-structured network. The rheological properties of the gels depended on the dose, PEO concentration and the amount of nanoparticles synthesized in the gels (initial Fe3+ content). Stronger gels with higher degree of intermolecular crosslinking were formed at higher dose and higher nanoparticle content. Magnetic iron oxide nanoparticles acted as reinforcing agents and additional crosslinkers of PEO chains facilitating gel formation in one step. All gels exhibited very good self-recoverable properties. SQUID magnetization measurements and Mössbauer spectroscopy showed that the samples exhibited superparamagnetic behavior even at very low temperatures. However, preliminary ac susceptibility measurements showed a deviation from Arrhenius' law ; the relaxation times of the composite hydrogels are unphysically small, suggesting that the particles interact with each other. Furthermore, in-field Mössbauer spectroscopy showed that the samples exhibit spin- canting phenomenon, presumably at the nanoparticle surface, forming a magnetically disordered shell with a ferrimagnetically ordered core.

magnetic hydrogel ; gamma-irradiation ; poly(ethyleneoxide) ; magnetite ; rheological properties ; Mössbauer spectrometry

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