Magnetic characterization of polyvinyl alcohol ferrogels and films
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uel Vázquez Instituto de Ciencia de Materiales, CSIC, 28049 Madrid, Spain
Carmen Mijangos Instituto de Ciencia y Tecnología de Polímeros, CSIC, 28006 Madrid, Spain (Received 28 April 2006; accepted 5 April 2007)
This study elucidates the tunability of the magnetic properties of cobalt spinel ferrites embedded in a polyvinyl alcohol (PVA) hydrogel by changing the structure of the polymer network. We report on the preparation and characterization of sPS-CoFe2O4 ferrofluid and PVA/sulfonated polystyrene (sPS)-CoFe2O4 ferrogels obtained by submitting the samples to a different number of freezing–thawing (F–T) cycles. The magnetic properties were evaluated and interpreted as a function of the PVA/sPS-CoFe2O4 composition and final structure of the ferrogels.
I. INTRODUCTION
Composite materials based on polymers are attracting much scientific and technological interest. Among all the possibilities, the homogeneous dispersion of nanometer scale inorganic species in a polymeric matrix is of great interest, as the polymeric material may gain specific rheological, optical, or electrical properties.1–3 In contrast to colloidal dispersions, nanoparticles dispersed in solids are generally assumed to be locked in place and to possess little if any mechanical freedom. The design of solids containing mechanically free nanoparticles in small cavities could lead to intelligent materials with unexpected properties for use in acoustical, electrical, magnetic, mechanical, optical, biomedical, or thermal applications.4 The stimuli-responsive properties of gels, for example, electric field, temperature, pH, visible light, salt, and solvent concentration have been widely studied.5–8 The magnetic fluid containing gel, or ferrogel, is one of the stimuli responsive gels, and it shows an abrupt elongation and contraction behavior by means of a magnetic field gradient.9 A ferrogel is a chemically cross-linked network swollen by a ferrofluid that is a colloidal dispersion of magnetic particles with a typical size of 10 nm, typically exhibiting magnetic single domain structure. The applications of these materials range from soft actuators in technical fields to applications in medicine where they might act as artificial muscles,10 carriers for drugs to guar-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0298 J. Mater. Res., Vol. 22, No. 8, Aug 2007
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antee controlled drug release,11 or for victims of hyperthermia due to the heating of magnetic gels in alternating external fields.12 It is possible to change the properties of these materials by altering the matrix in which the particles are either made or dispersed. Modifying the matrix, for example, could lead to changes in the composition, morphology, size, distribution, and attitude of the particulate, in the matrix–particle interaction or in the microstructure or nanostructure of the composite itself. Polyvinyl alcohol (PVA) is a unique synthetic biocompatible polymer, and it has a large
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