Preparation Of Nano Polyaniline And Its Functional Composite Materials By High Gravity Intensification Process

Due to its cheap raw materials, easy production, high conductivity, unique redox behaviors and relatively good solubility, polyaniline (PANI) nanomaterials have attracted widespread interest. Chemical oxidative polymerization is one of the most important method for preparing PANI nanomaterials in large scale, while high gravity technique is a new route for the intensification of chemical process. Based on these two techniques, our group created a high gravity chemical oxidative polymerization (HGCOP) method for preparing PANI nanofibers of high quality. In order to optimize the process and improve the properties of PANI, the different processes on the preparation of PANI were investigated in this research and the batch process was selected as the main research object, based on which the effects of additives on the product and the influence mechanism were researched, and the PANI nanofibers with improved properties and the PANI nanocomposites of high quality were obtained. The main contents are summarized as follows:1. The effects of the preparation process in RPB on the property of product were explored. Firstly, PANI nanofibers were prepared by HGCOP method with a batch process. Compared with the nanofibers prepared in STR, the nanofibers produced in RPB have little difference in the composition, structure, molecular weight and cycling stability as compared, but their specific surface area (49.1 m2/g) and conductivity (108.1 S/m) is increased by 26.2 and 15.2%, respectively. These advantages can greatly increase the effective utilization of PANI and speed up the charge transfer, and results in PANI nanofibers of up to 667.6 F/g. Secondly, Cubic PANI nanoparticles with a length of 100-150 nm were prepared using by a high gravity circulation method. Interestingly, these nanoparticles will tend to become nanofibers at higher temperature. Besides, the existence of ferric ions can hinder the formation of cubic nanoparticles. It should be noted that the cubic nanoparticles are susceptive to cause the second agglomeration and self-assemble into nanofibers during the drying process. The formation mechanism of cubic nanoparticles is probably due to the strong mixing effect of RPB which can break the assembly process of PANI nanoparticles. By comparison, batch process was selected as the basic method for the following experiments because its high stability and the large specific surface area of product were vital to the conductivity and electrochemical properties of PANI.2. To improving the morphology and property of PANI, AD and AP were used as additives in the preparation of PANI nanofibers by HGCOP method. In this research, the effects of additive dosage, reaction temperature and high-gravity level on the properties of product were investigated in detail. Results indicated that both AD and AP can greatly accelerate the reaction and promote the growth of PANI nanofibers. Thus, the aspect ratio of nanofibers was up to 19.4 and 37.4, and the maximum specific capacitance of PANI was 527.5 and 552 F/g for the products prepared with AD and AP, respectively. Due to their much lower oxidation potential, the additives will first form nucleation centers rather than aniline molecules. Therefore, they accelerate the reaction and make the growing environment of PANI tend to the homogeneous nucleation. As a result, the as-obtained PANI nanofibers with high aspect ratio can increase the effective utilization of PANI and speed up the charge transfer during the electrochemical reaction. Besides, it was proved that the molecular structure of the additive has great influence on the morphology of product.3. Multiwalled carbon nanotubes (MWNTs) were used as additive and the their effects on the preparation of PANI and the influence mechanism were studied. The effects of the MWNTs dosage and the functional group on MWNTs on the morphology and conductivity of products were researched in detail, and polyaniline/multiwalled carbon nanotubes (PANI/MWNTs) nanocomposites were obtained. Results indicated that the as-prepared nanocomposites exhibited uniform core-shell tubular structure with a diameter of 30-50 nm. The aniline groups on MWNTs took part in the polymerization of aniline and covalent bonds were formed between MWTNs and PANI by these aniline groups. The MWNTs in the products could form a conductive network which increased the conductivity of PANI by 9 times. Compared with stirred tank reactor (STR), the RPB used in the HGCOP method has more important influence on obtaining uniform PANI because of its good micromixing effect.4. Graphene (GN) sheets were used as additive and their effects on the preparation of PANI and the influence mechanism were studied. This work investigated the effects of GN dosage, aniline concentration and ammonium persulfate/aniline (APS/AN) mole ratio on the properties of products, and polyaniline/graphene (PANI/GN) nanocomposites were produced. It was found that the surface of GN sheets were uniformly covered with PANI nanoparticles and the thickness of coating can be tuned from 20 to 40 nm. Due to the synergistic effect between PANI and GN sheets, the specific capacitance of the nanocomposites (403 F/g) was increased by 26% as compared with pure PANI nanofibers. Aniline concentration can hardly affect the properties of product as long as the GN sheets can uniformly dispersed in the aniline solution. The specific capacitance of the product was further increased to 542 F/g at a proper APS/AN mole ratio. From the comparative experiment, it was established that the morphology affect the specific capacitance greatly because uniform and thin PANI coating has more exposed surface which can increase the effective utilization of PANI during the electrochemical reaction.