Thickness Of PPy Layer Research Articles

Electrical properties of intrinsically conductive core–shell polypyrrole/poly(vinylidene fluoride) electrospun fibers

Polypyrrole (PPy) has been synthesized as an homogeneous layer on the fibers of electroactive poly(vinylidene fluoride) (PVDF) electrospun mats via in-situ polymerization of pyrrole (Py). A core-sheath structure was obtained, the electrical conductivity depending on synthesis time, which influences the morphology and thickness of PPy layer. An overall dc conductivity of 70±4Sm−1 was obtained for the sample with a PPy layer of 160±25nm.Further, the thermal coefficient of resistivity obtained for the sample after 120min in-situ polymerization is almost twice the one calculated for the sample with 5min synthesis time. The temperature dependence of the electrical dc conductivity of the PPy/PVDF membranes gives evidence of a transport mechanism based on Mott's variable range hopping model. Using this model, values for the density of states, hopping energy and distance were assessed.

Preparation and Characterisation of Novel Composites Based on a Radiation Grafted Membrane for Fuel Cells

AbstractNovel composites for fuel cells were prepared via two different methods using a radiation grafted membrane, prepared from poly(ethylene‐alt‐tetrafluoroethylene) (ETFE) and styrene, and commercial Nafion®112 as the substrates. The first method was based on chemical polymerisation of pyrrole (Py) on the membrane followed by platinum (Pt) deposition by chemical reduction. The second method was based on direct deposition of Pt on the membrane by several steps of initial composite formation and surface electrodeposition. Polypyrrole (PPy) was coated as a layer only on the surface of the membrane. The thickness of PPy layer, proton conductivity of the composites and Pt loading could be controlled with Py polymerisation time. Moreover, the deposition of Pt on the surface as the granular particles was achieved by the first method while Pt deposition occurred as the aggregates of particles on the surface of the membrane by the second method which yielded wavy and rough surfaces. The first method offered a simple, quick, reproducible and effective procedure, yet some of the Pt particles peeled off from the surface of the composites. The second method required complex, multistep and tedious procedure with a high amount of Pt precursor, while Pt particles were more stable in this case.

The preparation of polypyrrole–Fe 3O 4 nanocomposites by the use of common ion effect

Fe 3O 4 nanoparticles were successfully disposed with FeCl 3 solution to prevent their aggregation in the solution by the application of common ion effect principle. A large amount of Fe 3+ was absorbed onto the surface of the Fe 3O 4 nanoparticles and formed positively charged (Fe 3+) shell. Consequently, the surface of the Fe 3O 4 nanoparticles became the active site to polymerize pyrrole monomers. The obtained composites were then characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM photos indicated that Fe 3O 4 nanoparticles treated with FeCl 3 solution were encapsulated by polypyrrole (PPy) matrix, and the dispersion of the resulting Fe 3O 4 nanoparticles was more stable than that of the control sample without FeCl 3 treatment. This kind of Fe 3O 4 nanoparticles was a stable composite system, and the thickness of PPy layer was about 10 nm. The formed composites showed unique electrical and magnetic behavior. The room temperature conductivity of PPy–Fe 3O 4 composites was higher than that of pure PPy, and went on increasing as the Fe 3O 4 content in the composites elevated, reaching a maximum at about 11.36 S cm −1. The saturated magnetization ( M s=6.89–16.98 emu g −1) also increased linearly with the Fe content in the composites, however, the coercive force ( H c) was very low ( H c=5–12 Oe). As a result, the obtained composites by this method were suitable for the preparation of soft magnetic material.