Eev

More recent work [85] has shown that the use of Tiron (Scheme 3) as dopant enables production of monodispersed polypyrrole particles of 50 nm (Fig. 11). Tiron has previously been shown to act as an electrocatalyst in the formation of polypyrrole [86].

2.2. Micellar Polymerization and Microemulsion Routes

A novel approach to the formation of ICP nanoparticles has been developed through the use of micellar polymerization and microemulsion techniques. The advantage of such an approach is that the particle size can be predefined by establishing the appropriate size and geometry of the tem-plating micelle (Fig. 12). For example, formation of polyani-line nanoparticles has been achieved via polymerization in a micelle approach using either sodium dodecyl sulfate (SDS) [87] or dodecylbenzenesulfonic acid [88-90] as the surfactant stabilizer. Particle sizes in the range of 10-30 nm with conductivities as high as 24 S cm-1 have been reported.

Poly(3,4-ethylenedioxythiophene) (PEDOT) and polyani-line nanoparticles have also been synthesised via the micellar route with sodium dodecyl sulfate and dodecylbenzene sulfonic acid [91]. Polyaniline nanoparticles were spherical and 20 to 60 nm in diameter and PEDOT was from 35 to 100 nm. The observed conductivities of 20 to 50 S cm-1 (by pellet) were higher than those observed for larger micrometer sized particles prepared in bulk solutions.

Control of the micelle size utilized in the formation of polyaniline nanoparticles has been achieved by tailoring the stabilizer to modify the resulting micelle dimensions. Kim et al. [92, 93] have used amphiphilic polymer molecules, hydrophobically end-capped poly(ethylene oxide), and varied the hydrophilic PEO midsection length to control the final micelle size. The micelle structures formed were referred to as flower type, with the aniline monomer and hexane cosolvent interacting with the hydrophobic end groups. The resultant nanostructures ranged from 20 to approximately 300 nm in size depending on the molecular weight of the hydrophilic PEO midsection.

Metallic and semiconducting nanoparticles have been routinely produced at the sub-5 nm scale for some time but it has been a challenge to produce polymer nano-particles smaller than this. Jang et al. [94] have reported the synthesis of polypyrrole nanoparticles at the 2 nm scale via a microemulsion route carried out at 3 °C. Pyrrole monomer was initially formed into micelles and then oxidized by ferric chloride. Typical surfactants used in

0 0

Post a comment