The Preparation And Properties Of Polypyrrole And Its Composites By Template Method

Polypyrrole （PPy） is a typical conductive polymer owing to its conjugated structureand show better properties in charge transportation after proper doping. It has potentialand broad application prospects in sensor, capacitor, conductive composites and solarcells. However, its poor thermal stability and processability limit the applications ofpolypyrrole. The fabrication of PPy using various templates becomes a researchingfocus in order to promote the conductivities and processability of the PPy.In our paper, PPy with various morphology, including nanotubes, nanofibers,nanoparticles and special shape were synthesized via in-situ chemical oxidativepolymerization with different soft or hard templates. The influence of experimentcondition on the morphology, conductivities, and thermal stability of PPy werediscussed and the possible mechanisms were explained in detail. The results showedthat surfactants acted as dopant and soft template in the process of preparing PPy.Oxidants not only initiated reaction, but also acted as dopant which entered into thepolymer molecule chains. Soft template and oxidants play a significant role in themorphology and conductivity of the PPy.Firstly, an oil-water microemulsion system containing sodium dodecylbenzenesulfonate （SDBS） or sodium dodecyl sulfate （SDS） was used to synthesize PPynanoparticles respectively via in-situ chemical oxidative polymerization. The resultsshow that PPy nanoparticles were synthesized by SDBS or SDS acting as soft templates.With an increase of the concentration of the SDBS, the particle size of PPy tended todecrease. Compared with SDBS, the PPy nanoparticles aggregated up to200nm withthe increasement of the concentration of the SDS. The conductivity of PPynanoparticles which were synthesized using SDBS as soft template was higher than thatusing SDS. The conductivity of PPy nanoparticles is about1.00S·cm-1when theconcentration of the SDBS is10CMC. The monomer was polymerized in the micellesof the surfactant and the micelles were adsorbed on the surface of MWCNTs in thesolution containing SDBS and MWCNTs. In addition, the concentration of surfactantand the amount of MWCNTs played a significant role in the improvement of thePPy/MWCNTs composites’ conductivity. The PPy/MWCNTs composites with excellentconductivity （5.68S·cm-1） were obtained when the concentration of the SDBS was10CMC and the mass ratio of the MWCNTs/monomer was0.20.Secondly, PPy was successfully synthesized in β-naphthalene sulfonic acid （β-NSA） or SDS aqueous solutions with different oxidants. Both soft template andthe oxidant worked on the morphology, composition and conductivity of the PPy. Theconductivity of PPy was determined by the type of soft templates when ferric chloride（FeCl₃） and ammonium persulfate （APS） were used as oxidants. However, the loweroxidation-reduction potential of oxidant had effect on the conductivity when copperchloride （CuCl2） was used as oxidant. When using different kinds of soft template,different structure and morphology of PPy were formed with silver nitrate （AgNO3） asoxidant. Ag/PPy composites prepared looked liked wires gathered with Ag and PPyparticles using β-NSA as soft templateand the samples prepared using SDS as softtemplate were microspheres with core-shell structure and the core was Ag particles andthe shell was PPy. The conductivity of the former is769S·cm-1and that of the latter is33.3S·cm-1. To investigate the influence of type of surfactants and FeCl₃/Py （molar ratio）on the conductivity of PPy, a series of PPy were synthesized in β-NSA, SDS or SDBSaqueous solutions. An intresting regulation was founed by the first time that theconductivity of PPy were highest when FeCl₃/Py （molar ratio） was1.1withsurfactants/monomer （molar ratio） being0.3. Elementary analysis showed that duringpolymerization the anion of surfactants entered into polymer conjugate chain. Theconductivity of PPy were determined by the type of surfactants and varied with thedoping level when the same oxidant was used. Thermogravimetric analysis （TGA） testshowed that the thermal stability of PPy which was prepared by SDBS was the best, thenext one was the product by SDS and the sample byβ-NSA was the worst.Finally, methyl orange （MO） is firstly used as soft template and dopant tosynthesize polypyrrole nanotubes by in-situ chemical oxidative polymerization methodwhen the molar ratio of the oxidant and monomer was1:1, using FeCl₃as oxidant. Theconductivity of PPy was determined by the type of oxidant and the doping of softtemplates. When using APS as oxidant, the diameter, wall thickness and length of PPynanotubes were300nm,30nm,10μm respectively. When using ferric chloride asoxidant, the above corresponding values of PPy nanotubes were200nm,20nm and10μm respectively. The difference in morphology is related to the oxidation-reductionpotential of oxidant and the doping level. The conductivity of PPy nanotubes were29.07S·cm-1and2.105S·cm-1when FeCl₃and APS were used as oxidant respectively.In addition, the aggregation shape of MO micelles in aqueous solution would changewith different pH value which decided the morphology of PPy, indicating MO acting assoft template in polymerization. In order to discuss the influence of the pH value of thesolution and MO concentration on the conductivity and morphology of PPy, a series of experiments were carried out with different usage of hydrochloric acid （HCl） and MO.The results illustrated the conductivity and morphology of PPy changed with differentpH value of the MO solution. The solubility of PPy was up to0.312g/L and theconductivity of PPy was lowest （0.025S·cm-1） when the usage of HCl and MO were0.7ml and0.098g respectively. The improvement of solubility of PPy was at expense ofits conductivity.