Thermal Analysis of Polyimide-Cobalt Ferrite Nanocomposites D. Mazuera * , O. Perales-Pérez ** , B. Rentería** and O. M. Suárez ** * University of Puerto Rico, Department of Mechanical Engineering, Mayagüez, Puerto Rico 00681 ** University of Puerto Rico, Department of Engineering Science and Materials, Mayagüez, Puerto Rico 00680-9044 ABSTRACT Thermal stability and thermomechanical behavior of a new polymer-based nanocomposite was conducted to assess the viability of its fabrication process. The nanocomposite films consisted of a polyimide matrix and dispersoids of 20nm cobalt ferrite single crystals exhibiting room- temperature coercivity of 2.9 kOe. For the sake of comparison, a bare polyimide film was also prepared. Infrared spectroscopy and x-ray diffraction analyses confirmed proper composite fabrication with development of expected phases. Dynamical mechanical analysis measurements of Tan δ and storage modulus as a function of temperature evidenced an increase in the viscous-like behavior of the composite film by incorporation of the ferrite nanocrystals within the polymeric matrix. The corresponding reduction in the storage modulus values were validated by thermo-gravimetrical analysis as a function of time and heating temperature in both, the bare polymer film and the nanocomposites. Keywords: PMC, magnetic nanocomposite, cobalt ferrite, polyimide, thermal analysis. 1 INTRODUCTION Polymer matrix magnetic composites and nanocomposites, commonly referred to as magnetic polymers, are receiving an increasing interest due to their wide range of potential applications: polymer bonded magnets, microelectromechanical systems (MEMS), microsensors, high density storage and magneto-optical media, electromagnetic shielding, cell separation, medical diagnosis, controlled drug delivery, etc [1-15]. Their relative low cost and light weight are appealing factors when compared to metallic or ceramic magnets. Their high formability and machinability, and the possibility of bearing outstanding magnetic properties due to the incorporation of nanosize dispersoids make these composites the material of choice to fabricate micro- or macro-scaled devices with the typical advantages of using polymer matrices [9, 16]. Regarding the disperse phase, it has been already demonstrated the possibility of tuning the magnetic properties of cobalt ferrite nanoparticles by a precise control on their crystal size within the single domain region. This type of control leads to outstanding values of coercivity compared with typical values of the bulk [17] and enables this nanomaterial to be considered a suitable dispersoid in polymer-based composites for use in microelectronic and sensing devices [1, 5, 15]. However, since cobalt ferrite particles would behave as nanosize permanent magnets (because of its high coercivity and residual magnetic induction) they tend to cluster together making their homogeneous dispersion within the matrix a challenging task. In this work, 20 nm cobalt ferrite single crystals, which exhibited a coercivity of 2.9kOe at room- temperature, were use as dispersoids (10% and 20% ferrite volume fraction) in a polyimide matrix. A high spindle speed homogenizer was used to improve the dispersion conditions. The thermomechanical properties of the resulting nanocomposites were determined as a function of the volumetric load of the ferrite nanocrystals. The thermal stability and thermomechanical properties of the composite films were carried out by using thermo gravimetrical analysis (TGA) and dynamical mechanical analysis (DMA), techniques. The obtained results were used to assess the feasibility of the nanocomposite fabrication. 2 EXPERIMENTAL 2.1 Materials All reagents were of analytical grade and were used without further purification. Required weights of chloride salts of Fe(III) and Co(II) ions were dissolved in distilled water to achieve a mole ratio Fe/Co of two. NaOH was used as the precipitating agent. Commercial polyimide precursor (Dupont PI2555) and isopropyl trisostearyl titanate (Kenrich Prtrochemicals KR-TTS) were used as- received. 2.2 Synthesis of Cobalt Ferrite Nanocrystals Cobalt ferrite nanocrystals were synthesized by a modified coprecipitation method. An aqueous solution of 0.11M Fe(III) and 0.55M Co(II) was continuously added by controlled flow rate into the reaction vessel containing an aqueous solution of 0.48M NaOH under boiling conditions. The vessel was heated for one hour to allow dehydration and atomic rearrangement involved with the conversion of the precursor hydroxide into the ferrite structure. Ferrite nanocrystals were magnetically decanted, washed NSTI-Nanotech 2009, www.nsti.org, ISBN 978-1-4398-1783-4 Vol. 2, 2009 467