J Nanopart Res (2009) 11:1441–1452 DOI 10.1007/s11051-008-9531-8 RESEARCH PAPER Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites Zhanhu Guo Æ Koo Shin Æ Amar B. Karki Æ David P. Young Æ Richard B. Kaner Æ H. Thomas Hahn Received: 8 July 2008 / Accepted: 2 October 2008 / Published online: 31 October 2008 Ó Springer Science+Business Media B.V. 2008 Abstract The effect of iron oxide nanoparticle the PPy in the nanocomposites was enhanced under addition on the physicochemical properties of the the thermo-gravimetric analysis (TGA). The electri- polypyrrole (PPy) was investigated. In the presence cal conductivity of the nanocomposites increased of iron oxide nanoparticles, PPy was observed in the greatly upon the initial addition (20 wt%) of iron form of discrete nanoparticles, not the usual network oxide nanoparticles. However, a higher nanoparticle structure. PPy showed crystalline structure in the loading (50 wt%) decreased the conductivity as a nanocomposites and pure PPy formed without iron result of the dominance of the insulating iron oxide oxide nanoparticles. PPy exhibited amorphous struc- nanoparticles. Standard four-probe measurements ture and nanoparticles were completely etched away indicated a three-dimensional variable-range-hopping in the nanocomposites formed with mechanical conductivity mechanism. The magnetic properties of stirring over a 7-h reaction. The thermal stability of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide Z. Guo Á H. T. Hahn Multifunctional Composites Lab (MCL), Mechanical & nanoparticles from dissolution in acid. A tight Aerospace Engineering and Materials Science & polymer structure surrounds the magnetic nanoparti- Engineering Department, University of California, cles, as compared to a complete loss of the magnetic Los Angeles, CA 90095, USA iron oxide nanoparticles during conventional Present Address: mechanical stirring for the micron-sized iron oxide Z. Guo (&) particles filled PPy composite fabrication. Chemical Engineering Department, Lamar University, Beaumont, TX 77710, USA Keywords Polymer nanocomposites Á e-mail: [email protected] Conductivity Á Stirring methods Á Magnetic property Á K. Shin Thermal stability Á Corrosion-resistance Á Department of Applied Chemistry, Sejong University, Nanomanufacturing Seoul 143-747, South Korea A. B. Karki Á D. P. Young Department of Physics and Astronomy, Louisiana State Introduction University, Baton Rouge, LA 70803, USA Polypyrrole (PPy), a conducting conjugated polymer, R. B. Kaner Department of Chemistry and Biochemistry, University of has attracted much interest due to its low cost, easy California, Los Angeles, CA 90095, USA synthesis, good stability, and environmentally benign 123 1442 J Nanopart Res (2009) 11:1441–1452 performance (Yeh et al. 2003). The conductivity of a PPy synthesis, will etch away the nanoparticles in conductive polymer is strongly dependent on the aqueous solutions. A balance between the need for doping agents (dopant) with electron donor or polymerization in an acidic solution and the pre- acceptor abilities. The doping process can even vention of dissolution of reactive iron oxide transform an intrinsically conjugated polymer insu- nanoparticles will be a determining factor for high- lator to a near-metallic conductor (Lee et al. 2006). quality nanocomposite fabrication. Conductive PPy has been reported to serve as Polypyrrole nanocomposites with iron oxide and polymeric rechargeable batteries for energy-storage other nanoparticles have been prepared by several purposes (Song and Palmore 2006), electrode mate- methods. For example, an in situ chemical oxidative rials used in the electrochemical supercapacitors polymerization approach with either an ultrasonication (Ingram et al. 2004; Noh et al. 2003), metal corrosion approach (Yen et al. 2008) or mechanical stirring protection coating materials (Ferreira et al. 1990; approach (Li et al. 2006) was reported. The nanocom- Zaid et al. 1994), matrix for structural composite posites showed particle-loading magnetic properties materials (Han et al. 2005), electromagnetic interfer- and electric conductivity. In addition, the supercritical ence (EMI) shielding, electrochemomechanical fluid was also reported to be used as a media in the in devices (Asavapiriyanont et al. 1984), and sensors situ chemical oxidative polymerization for the fabri- for pH (Lakard et al. 2007), gas, and humidity cation of the conductive polymer magnetic nano- (Tandon et al. 2006; An et al. 2004) testing. In composites with a consideration of green chemistry addition, granular polypyrrole nanocomposites have (Yuvaraj et al. 2008). The stirring method (ultrason- been reported as a candidate for photovoltaic (solar ication or mechanical stirring) is believed to have a cell) materials (Kwon et al. 2004). significant effect on the formed nanocomposites and Polymer nanocomposites with nanoparticles (NPs) the subsequent physicochemical properties. However, have attracted much interest due to their homogene- there are few papers reported in the literature. ity, easy processability, and tunable physical In this paper, the effect of iron oxide nanoparticle (mechanical, magnetic, electrical, thermoelectric, addition on the morphology of PPy, thermal stability, and electronic) properties (Castro et al. 2000; Wang magnetic properties, and electrical conductivity of the et al. 2000; Gangopadhyay et al. 2000; Corbierre resulting Fe2O3/PPy nanocomposites was reported. et al. 2001; Li et al. 2002; Wetzel et al. 2003; Mack The effect of the stirring method, i.e., ultrasonic and et al. 2005; Chen et al. 2005; Vivekchand et al. 2005; mechanical stirring on the composite fabrication was Mammeri et al. 2005; Guo et al. 2006; Lee et al. also reported. The electric conductivity was investi- 2008). High particle loading is required for certain gated by a standard four-probe method and found to industrial applications, such as electromagnetic wave be strongly dependent on the particle loadings. The absorbers (Brosseau and Talbot 2005; Guo et al. iron oxide nanoparticles were observed to be stable 2007a), photovoltaic cells (solar cells) (Beek et al. even after exposure to a strong acid with a pH value 2004), photo detectors, and smart structures (Gall of 1.0 for more than 3 weeks. et al. 2004; Mohr et al. 2006; Guo et al. 2007b). Magnetic nanoparticles, due to their unique magnetic and electronic properties, are used in various appli- Experimental details cations such as biomedical drug delivery, specific site targeting, magnetic data storage and sensors (Toal Materials and Trogler 2006; Podlaha et al. 2006; Lei and Bi. 2007; Bi et al. 2008). Successfully incorporating The pyrrole monomer (Aldrich) was distilled under magnetic nanoparticles into conductive polymer reduced pressure. c-Fe2O3 nanoparticles were matrices will definitely widen their applicability in obtained from Nanophase Technologies Corporation the fields of electronics, biomedical drug delivery, with a reported average size of 23 nm and a specific and optics. However, one of the challenges so far is surface area of 45 m2/g. Ammonium persulfate the ability to integrate a high fraction of nanoparticles (APS) and p-toluenesulfonic acid (CH3C6H4SO3H, into the polymer matrix in a strong acidic environ- p-TSA) were all purchased from Aldrich and used as ment. The acid, which is normally required for the received without further treatment. 123 J Nanopart Res (2009) 11:1441–1452 1443 Polypyrrole and nanocomposite preparation layer of powder onto a double-side carbon tape. The microstructure and crystallinity were investigated A dispersion of c-Fe2O3 nanoparticles was made by with a transmission electron microscope (TEM, adding a desired amount of c-Fe2O3 in 20 mL JEOL, 100CX) with an accelerating voltage of deionized water under sonication. The p-TSA 100 keV. The samples were prepared by dispersing (6.0 mmol) and pyrrole (7.3 mmol) were added into the powder in anhydrous ethanol, dropping some the above nanoparticle suspended solution under suspended solution onto a carbon-coated copper grid constant sonication and continuously stirred for and drying naturally under ambient conditions. 10 min. APS (3.6 mmol) was rapidly mixed into the The magnetic properties of the nanocomposite above solution at room temperature, and the resulting were investigated in a 9-Tesla physical properties solution was kept under sonication for 1 h. In measurement system (PPMS) by Quantum Design. addition, the effect of reaction time was investigated The electrical conductivities were measured using a by sonication for 7 h as used previously in a study of standard four-probe method. The samples were the micron-sized iron oxide particles (Li et al. 2006). prepared by the cold-press method. The applied Both mechanical and ultrasonic stirring were pressure was 10,000 psi and the pressing duration explored, and the resulting nanocomposite properties time was 10 min. were characterized accordingly. All the products were washed thoroughly with deionized water (to remove any unreacted APS and p-TSA) and methanol Results and discussion (to remove any oligomers), respectively. The precip- itated powder was dried at 50 °C for further analysis. Figure 1 shows the SEM microstructures of the As a control experimental for comparison purposes, synthesized pure PPy and Fe2O3/PPy nanocomposites pure PPy was also synthesized following the same fabricated