Browsing by Author "Islam, SMKN"

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    Interplay between thermal and magnetic properties of polymer nanocomposites with superparamagnetic Fe3O4 nanoparticles
    (Elsevier, 2023-08-01) Rezoanur Rahman, M; Bake, A; Jumlat Ahmed, AI; Islam, SMKN; Wu, L; Khakbaz, HS; FitzGerald, S; Chalifour, A; Livesey, KL; Knott, JC; Innis, PC; Beirne, S; Cortie, DL
    Magnetic nanoparticles embedded in polymer matrices have excellent potential for multifunctional applications like magnetic remote heating, controlled drug delivery, hyperthermia, and thermally functionalized biomedical devices. A solvent-based processing method was developed to produce magnetic composites consisting of magnetite (Fe3O4) superparamagnetic nanoparticles embedded in a biomedical-grade polyurethane (ChronoFlex® C). The particles had a log-normal size distribution spanning from 4−16 nm, with a mean-size of 9.5 ± 2 nm. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy with elemental mapping were used to assess the phase purity, surface morphology, particle size, and homogeneity of the resulting nanocomposite. The magnetic properties of composites with 7–13 wt% of Fe3O4 were studied between 5 and 300 K using vibrating sample magnetometry. Room temperature magnetic attraction was observed, with a saturation magnetization of up to 5 emu/g and a low coercive field (Hc < 50 Oe), where the non-zero coercive field was attributed to a small fraction of larger particles that are ferromagnetic at room temperature. Field-cooled and zero-field-cooled magnetometry data were fitted to a numerical model to determine the superparamagnetic mean blocking temperature (TB = 90 K) of the embedded magnetite particles, and an effective magnetic anisotropy of 6×105 erg/cm3. Using an AC magnetic field operating at 85 kHz, we demonstrate that remote heating of the base polyurethane material is greatly enhanced by compositing with Fe3O4 nanoparticles, leading to temperatures up to 45 °C within 18 min for composites submerged in water. This work demonstrates the fundamental principles of a custom-designed thermomagnetic polymer composite that could be used in applications, including medical and heat management. © 2023 Published by Elsevier B.V.
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    Ultra-high thermoelectric performance in graphene incorporated Cu2Se: role of mismatching phonon modes
    (Elsevier, 2018-11) Li, M; Cortie, DL; Liu, J; Yu, DH; Islam, SMKN; Zhao, L; Mitchell, DRG; Mole, RA; Cortie, MB; Dou, SX; Wang, XL
    A thermoelectric material consisting of Cu2Se incorporated with up to 0.45 wt% of graphene nanoplates is reported. The carbon-reinforced Cu2Se exhibits an ultra-high thermoelectric figure-of-merit of zT = 2.44 ± 0.25 at 870 K. Microstructural characterization reveals dense, nanostructured grains of Cu2Se with multilayer-graphene and graphite agglomerations located at grain boundaries. High temperature X-ray diffraction shows that the graphene incorporated Cu2Se matrix retains a cubic structure and the composite microstructure is chemically stable. Based on the experimental structure, density functional theory was used to calculate the formation energy of carbon point defects and the associated phonon density of states. The isolated carbon inclusion is shown to have a high formation energy in Cu2Se whereas graphene and graphite phases are enthalpically stable relative to the solid solution. Neutron spectroscopy proves that there is a frequency mismatch in the phonon density of states between the carbon honeycomb phases and cubic Cu2Se. This provides a mechanism for the strong scattering of phonons at the composite interfaces, which significantly impedes the conduction of heat and enhances thermoelectric performance. © 2018 Elsevier Ltd. A