Magnetic field dependence of the diffusion of single dextran molecules within a hydrogel containing magnetite nanoparticles |
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Authors: | Al-Baradi Ateyyah M Mykhaylyk Oleksandr O Blythe Harry J Geoghegan Mark |
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Institution: | Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom. |
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Abstract: | We consider the effect of applied magnetic fields on the diffusion of single dextran molecules labeled with fluorescein isothiocyanate within a ferrogel a composite of magnetite nanoparticles in a poly(methacrylic acid) hydrogel] using fluorescence correlation spectroscopy. We show that the mesh size of the ferrogel is controlled by the applied magnetic field, B, and scales as exp(-(4)√ξ(3)B(2)/2μ(0)k(B)T), where ξ is a correlation length, μ(0) the magnetic constant, k(B) the Boltzmann constant, and T is the absolute temperature. The diffusion coefficient of the dextran can be modeled with a simple Stokes-Einstein law, containing the same scaling behavior with magnetic field as the swelling of the hydrogel. Furthermore, the magnetic field-dependent release of dextran from the hydrogel is also controlled by the same relationship. The samples were characterized by small angle x-ray scattering (SAXS) and magnetometry experiments. Magnetic hysteresis loops from these ferrogels and zero field cooled∕field cooled measurements reveal single domain ferromagnetic behavior at room temperature with a similar coercivity for both as-prepared and fully swollen ferrogels, and for increasing magnetic nanoparticle concentration. SAXS experiments, such as the hysteresis loops, show that magnetite does not aggregate in these gels. |
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