Synthesis, Charaterization And Application Of Nanostructured Polyaniline

As one of the most promising conducting polymers, polyaniline (PANI) has received comprehensive studies in recent years owing to its advantages including easy preparation, cheap materials, unique doping mechanism and good chemical and environmental stability. Up to now, PANI has been widely used in many fields, such as gas sensors and electric devices. However, the difficulty to dissolve in the common solvents limits its further application.In order to overcome the above problem, people have tried to improve the characteristics of PANI through different processes, such as doping by functional acids or copolymerization with other materials. Recently, people are focusing on preparation of nanostructured PANI because of its good water-dispersity. Furthermore, the nanostructured PANI has large surface area and porous property, which greatly improve its application in sensors and electric devices. Besides, preparation of PANI dispersions is also an effective way for the convenient application of PANI.Based on the above background, we selected the preparation of PANI nanofibers and dispersions in order to improve the processability of PANI. As for the preparation of PANI nanofibers, we first provided a novel"seed"polymerization, during which the aniline was polymerized using PANI (from conventional polymerization)/dimethyl sulphoxide (DMSO) solution as"seed". The"seed"helped accelerating the polymerization process of aniline and impeded the secondary growth of the newly formed PANI nanofibers. Finally, we obtained PANI nanofibers with uniform morphology and high conductivity. We further found that only addition of organic solvents that are co-dissolvable with water to the polymerization system of aniline led to obtain PANI nanofibers. We considered it was originated from the H-bond interaction between the organic solvents and PANI that helped dispersing and hence avoiding the aggregation of the newly formed nanofibers. Besides, we chose two kinds of organic solvents, including the ones dissolvable and undissolvable with water. The aniline dissolved in the above organic solvents was used as"seed"and added into the acid solution of the oxidant to initiate the polymerization of the aniline. Using this method, we also obtained PANI nanofibers. The formation mechanism of the nanofibers was discussed based on the H-bond interaction and the interfacial polymerization mechanism.To prepare PANI dispersions, we selected a common surfactant, sodium dodecyl benzene sulfonate (SDBS) to construct dispersion system for the polymerization of aniline. We focused on the investigation on the macroscopic morphology of the dispersions in order to study their self-assembly structure, which was often ignored by the former researchers. We found the dispersions showed network structure owing to the interaction between PANI and the surfactant. By changing the preparation conditions, PANI dispersions with different compact degrees and stability could be obtained. Based on the successful preparation of stable PANI dispersions, we also carried out the polymerization of pyrrole in the obtained PANI dispersions and investigated the feasibility of the complex of PANI and other materials in its dispersion form. The results showed good PANI/polypyrrole (PPy) composites could be obtained from the stable dispersion systems.The application of PANI is mainly related to the study of sensors and electric devices. Aim to that, we first investigated the response of the nanostructured PANI films obtained from rapidly mixing reaction to NH3. We considered the porous property and high surface area made the films behave high response and be recovered easily. On the other hand, we fabricated a new type of unilateral conductive diode through contact assembly of PANI and Pt films. The movement of the PANI film might be the drive force to form such characteristic that was proved by micro linescan IR spectra. When a negative voltage was added on the sample, the PANI was away from the interface between the PANI and Pt films, while it came back or crossed the interface with a forward bias on the sample, which made the sample nonconductive and conductive accordingly. Though the preparation of the device and unilateral conductive mechanism are not perfect, we are sure it will provide a new way for the fabrication of the electric devices based on conducting polymers.