| During the last decades, conductive polymers have captured high attention in different applications because of the obvious advantage in many fields. Among all of topics, improvement of conductivity, processing performance and the ability of energy storage are the hot topics.For the conductive performance improvement, can be achieved by improving the method of polymerization, improved methods of doping or the improvement of the aggregation structure; For the improvement of processing performance, is mainly concentrated in the soluble and/or dispersible directions; For the performance of the energy storage, is mainly to increase the surface area, to enhance the reusability, and to improve electrochemical performance, and so on. The properties of polyaniline are interrelated and constraints together and cannot be discrete. Thus, many different methods have been used to achieve these goals. Compared to other conductive polymers, polyaniline attracted the most attention, because it has a superior thermal stability, better processing properties and electrical conductivity, the monomer is easily obtained, the synthesis methods is simple and varied.Among the synthesize methods of polyaniline, the chemical polymerization which uses ammonium persulfate (APS) as initiator is the most simple and convenient mehod, and is also expected to promote the application method.It is based on the aqueous phase as the polymerization environment; the oil-soluble aniline monomer is initiated by a water-soluble initiator ammonium persulfate. This leads to unevenness of the reaction, and in the high pH will produce defective branched structure. The presence of non-uniformity of the product and defect structure will have a huge impact on the performance of the final material. The surfactant composition of the EO chain and the PO chain is also ion-conductive polymer and a polymer solvent. As an ion-conductive polymer, it can play the role of a bridge in polyaniline conducting in order to facilitate the improvement of conductivity. As the polymer solvent, it can dissolve the impurity ions introduced in the polymerization and doping process. Pluronic PI23(EO20PO70EO20) and Pluronic F127(EO106PO70EO106) are triblock copolymer constituted by the EO chain segment and the PO chain segment, holding the above characteristics. At the same time, as a triblock copolymer surfactant, it will be controllable self-assemble into a variety of special morphology, and often is used as a template of controllable morphology synthesis. Polyvinyl alcohol (PVA) having a structure similar to them, is a water-soluble polymer and possess excellent hydrophilicity, which can be used for the preparation of water-soluble polyaniline. From PPG to Pluronic PI23, Pluronic F127, PEG, as well as PVA, the hydrophilic is enhanced. They are all belonging to non-ionic polymeric surfactant and have a trimly arranged oxygen atoms in their structure which could form the hydrogen bond interaction with hydrogen atoms in aniline and further induce an ordered structure of polyaniline.Based on this case, a series of nonionic polymeric surfactants, PEG, Pluronic F127, Pluronic PI23, PPG and PVA, were chosen to introduce in polyaniline synthesize process and studied the influence of these surfactants category, molecular weight, hydrophilic and concentration on the polyaniline, which will deal with their synthesis, structure, stability, physicochemical properties, electrochemical performance, etc. In order to facilitate comparison with sulfonic surfactant, the dopant is sulfonic acid. Furthermore, the PEG with different molecular weight was also selected for investigation the effect of molecular weight on polyaniline conductivity. The products with different characteristics and performance were obtained under different conditions.Compared to previous studies, the novelty include as follows:(1) Improved the most common chemical polymerization synthesis method which is simple and convenient, avoid the special requirements process;(2) Induced by aniline to produce a more regular structure in the polymerization use of the special structure of such surfactants;(3) Separated the dopant and surfactant, avoid introducing impurity in the highly doped concentration;(4) Combining polyaniline with ionic conductive polymer together, so as to achieve the purpose to improve the conductivity of the polyaniline by using of the role of a bridge in the charge transfer process of ion-conductive polymer;(5) The surfactants used in this literature were selected systematically and representatively, has some aspects of scientific significance in explicating the function of surfactant in the synthesis of polyaniline;(6) The products with different characteristics and performance were obtained under different conditions.The main conclusions are as follows:(1) Introduction of these surfactants changed the electronic structure of polyaniline to some extent, cut down the π-π*transition energy, which is favorable in improvement of polyaniline conductivity.(2) The hydrophobicity of surfactant affects the final doping ratio under the same initial dopant concentration.(3) These surfactants played a good role in promoting the polyaniline forming ordered structure, and even led it hold aggregation structure similar to the crystal when introduction of PEO, Pluronic F127and Pluronic P123in synthesis process. Through derived by theoretical calculation, we infer that the crystal structure polyaniline most likely belongs to the monoclinic system, which is the same as the graphite crystal. These structures are beneficial to carrier pass in polyaniline chain. The polyaniline synthesized under acid condition is amorphous, which might due to the destructive effects of acid on the hydrogen bond and the introduction of impurity ions.(4) The thermal stability of polyaniline increase and then decrease along with the increase of surfactant concentration.(5) The conductivity of polyaniline increase and then decrease along with the increase of surfactant concentration, hi this experiment, it can be promoted two orders of magnitude. The room temperature conductivity of polyaniline increased from0.052S cm-1to6.67S cm-1(PEG20000),6.67S cm-1(Pluronic F127),6.67S cm-1(Pluronic P123),10.0S cm-1(PPG2000) and10.53S cm-1(PVA1788) after introduction of surfactant, respectively. These values are within the scope of conductive of semiconductor, illustrated that these polyaniline are good semiconductor materials. The conductivity of polyaniline increases with the introduction of surfactant is a comprehensive range of factors.(6) Introduction of PVA could broaden the application voltage range of polyaniline.(7) Effect of surfactant on polyaniline’s electrochemical performances is a very special regularity being similar to surface tension change in aqueous solution along with surfactant concentration. In other word, the surface characteristics have a decisive impact on specific capacitance. The as-prepared polyaniline possess a substantial specific capacitance under suitable condition. The as-prepared polyaniline possess almost ideal capacitor behavior and excellent ability of energy storage; shorten ion diffusion path and small internal impedance. Introduction of PEG is good for improvement of cycle life. However, introduction of other surfactants is disadvantage in cycle life.(8) The method includes Pluronic F127and Pluronic PI23is morphology controllable. The morphology change of polyaniline is same as self-assembly behavior of Pluronic F127and Pluronic PI23in aqueous solution. The morphology of polyaniline might due to copy of the morphologies of Pluronic F127and Pluronic P123self-assembly in aqueous solution. Addition of acid affects the morphology in some extent. The concentration of aniline affects the morphology in some extent.(9) The polyaniline synthesized in presence of Pluronic PI23possess well dispersibility so as to could be dispersed in several common solvent. Polyaniline has a certain solubility in DMF, DM Ac, DMSO and THF. Thus, these solvent cannot be used in preparing process of polyaniline for controllable morphology based devices.(10) The polyaniline synthesized in presence of PVA1788has certain solubility in water, and increase with increasing of PVA1788concentration.The well aggregation structure and high conductive might be related to the order molecular structure of these surfactant and large number of oxygen atom in them. The monomer would configuration along with this ordered chain and finally produces the order structure, too. Meanwhile, these surfactant, as polymeric solvent (except PVA), could dissolve the impurity ions which imported in synthesize process; avoid effect of them on structure and conductivity.The dissertation is just the preliminary research and discussion on effect of the serious non-ionic polymeric surfactants for polyaniline synthesis and properties. Due to the design requirements, it not includes other factors. Such as, there is a great degree of improvement on electrical conductivity if change the dopant from sulfonic acid into hydrochloric acid. The conclusions have certain scientific significance in the research proposition of introduction surfactant in polyaniline synthesis process. |
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