Superparamagnetic Flexible Substrates based on Submicron Electrospun Estane Fibers Containing MnZnFe-Ni Nanoparticles
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Superparamagnetic Flexible Substrates based on Submicron Electrospun Estane® Fibers Containing MnZnFe-Ni nanoparticles Pankaj Gupta1, Ramazan Asmatulu2, Rick Claus2 and Garth Wilkes1, 1 Department of Chemical Engineering (0211), 2 Fiber and Electro Optics Research Center (0356), Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 ABSTRACT Flexible field responsive superparamagnetic substrates were prepared by electrospinning a solution of elastomeric polyurethane containing ferrite nanoparticles (ca. 14 nm) of Mn-Zn-Ni. The flexible mats were characterized in terms of fiber morphology and magnetic properties. Field Emission Scanning Electron Microscopy (FESEM) indicated that the diameter of these composite fibers was ca. 300-500 nm. Furthermore, the back-scattered electron FESEM images indicated agglomeration of the nanoparticles at higher wt% (ca 17-26 wt%) loading in the electrospun fibers. The induced specific magnetic saturation and the relative permeability were found to increase linearly with increasing wt% loading of the ferrite nanoparticles on the submicron electrospun fibers. A specific magnetic saturation of 1.7 – 6.3 emu/g at ambient conditions indicated superparamagnetic behavior of these composite electrospun substrates. Additionally, dielectric constant values of the electrospun fibers were measured to be between 2.3 and 5.8. INTRODUCTION The ability to produce one-dimensional magnetic nanostructures in the form of fibers is very attractive as these are expected to exhibit interesting magnetic-field dependent properties. These materials could be used as active components for ultra-high density storage applications,[1] as well as in the fabrication of sensors [2,3]. Ferrites are widely used in many industrial applications due to their spontaneous magnetization. Therefore, the development of new and cost-effective techniques for fabricating one-dimensional nanostructures based on ferrites is of great commercial and scientific interest. In particular, soft ferrites [4-6] of Mn-Zn, Ni-Zn and Mg-Mn are well known for their high magnetic permeability [7]. Current research efforts [8] have been focused on synthesizing nanometer sized (5-20 nm) ferrite particles to minimize energy losses associated with bulk systems. Below a diameter of ca. 100 nm, particles of mixed [9] ferromagnetic materials (such as ferrites of Mn-Zn-Ni), do not exhibit the cooperative phenomenon of ferromagnetism found in the bulk as the thermal vibrations are sufficient to reorient the magnetization direction of the magnetic domains [10]. As a result, such nanoparticles display paramagnetic behavior at ambient conditions, thereby imparting a superparamagnetic behavior. When incorporated in submicron (200-500 nm) polymeric fibers, flexible superparamagnetic materials can be produced in a relatively convenient and costeffective fashion. In the present investigation, we report the processing of such substrates where nanoparticles of a mixed ferrite of Mn-Zn-Ni were incorporated in submicron (200-500 nm) fibers
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