Conducting Polypyrrole Shell as a Promising Covering for Magnetic Nanoparticles

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Conducting polymers are a recent generation of polymers, opening the progress in understanding the fundamental chemistry and physics of -conjugated macromolecules. Among conducting polymers, polypyrrole (PPy) has attracted great interest owing to its high conductivity and relatively high environmental stability, therefore the potential applications of polypyrrole are numerous. The combination of PPy with other inorganic materials in order to prepare composites which combine the properties of both materials is a very promising way to extend the application field of PPy but also of the inorganic materials. In order to improve the poor processability of polypyrrole a lot of methods have been explored in the preparation of soluble or swollen PPy (Masuda et al., 1989; Stanke et al., 1993) and dispersible fine powdered PPy (Bjorklund & Liedberg, 1986; Armes, et al., 1987; Cawdery et al., 1988; Aldissi & Armes, 1991). To extend the application field of polypyrrole, sterically stabilized PPy colloids were synthesized in aqueous media by chemically polymerizing pyrrole monomers in the presence of a suitable water-soluble polymer, such as methyl cellulose or poly(vinyl alcohol) (Armes et al., 1987; Armes & Vincent, 1987). The preparation of core-shell structures based on polypyrrole were first reported by Yassar et al. long before polypyrrole based magnetic core shell nanoparticles were developed. The authors coated latex particles by conducting polypyrrole (Yassar et al., 1987). After this many research groups reported the preparation of colloidal conducting polypyrrole by coating particles with a thin layer of conjugated polypyrrole to form conducting composites with a core-shell structure. Most of them were non-magnetic. Different types of polymers, metals and metal oxides were used as shells. Many papers describe the polymerization of pyrrole in the presence of different polymers structure, polystyrene being the most often used. (Lascelles & Armes, 1995; Lascelles et al., 1997; Lascelles & Armes, 1997; Cairns & Armes 1999; Lu et al., 2003; Bousalem et al., 2003; Bousalem et al., 2004a; Bousalem et al., 2004b; Bousalem et al., 2005; Benabderrahmane et al., 2005; Mangeney et al., 2006; Yip et al., 2006; Lee et al., 2009; Wang et al., 2009). Latex particles having a poly(butyl methacrylate) (PBMA) core of about 700 nm and a very thin polypyrrole (PPy) shell were reported by Huijs & Lang 2000. Further studies illustrated the effect of the thickness of the polypyrrole shell on latex properties (Huijs et al., 2001). Other ways to water-based processable conducting polypyrrole are based on the preparation of colloidal core-shell polypyrrole nanoparticles by oxidative polymerization of pyrrole in the presence of ultrafine silica nanoparticles. (Maeda & Armes, 1994; Azioune et