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The Preparation and Structure of the Self-suspended Polyaniline and the Characteristics of Its Composites

Author: HuangJing
Tutor: WangJun; XiongChuanXi
School: Wuhan University of Technology
Course: Composite materials science
Keywords: Polyaniline self-suspended polyaniline solution polymerization solvent-free nanofluids rheological property
CLC: O633.21
Type: PhD thesis
Year: 2013
Downloads: 60
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Abstract

In the past decades, polyaniline (PANI) has been one of the lasting hot spot in the researches on electric conductive macromolecules due to its diverse molecule structures, superior electric conductivity, unique doping mechanism, excellent physical properties, favorable environmental stability, low-cost raw materials and facile synthetic method. However, the extensive exploitation of these fascinating properties has always been restricted from the poor dispersibility of PANI in other polymer matrix. Therefore, the improvement of its processability promises great theoretical and practical significance for various applications of PANI and PANI based hybrids. In this dissertation, three types of self-suspended PANIs were successfully prepared, and the property-structure relationship and forming mechanism based on these PANI derivatives have been fully discussed. The main contents and results are as follows:(1) The typical preparation of self-suspended PANI followed a one-step strategy. Macromolecular PANI was obtained via bulk polymerization from aniline monomers, and in situ chemically doped by the organic long-chain proton acid, namely nonylphenol polyoxyethylene ether sulfoacid-10(NPES). The as-prepared self-suspended PANI demonstrated excellent solubility in various solvents and displayed the characteristic viscoelastic behaviors of thermoreversible gel. Furthermore, it’s found the morphological structures of final products which were closely correlated to the content of NPES (fNPES), can be calculated by thermal gravimetrical analysis (TGA). Particularly, when fNPES>0.6, the PANI presented two phase structure, the flowable continuous phase and dispersion phase of spherical micelles. Partial liquid crystalline structures were also identified in the polarizing microscope (POM) images.(2) Aniline trimer, tetramer, pentamer were prepared by chemically oxidative coupling and the results from X-ray diffraction revealed crystalline nature for all three aniline oligomers. It was worth noting that the tetramer showed a much higher crystallinity. UV-Vis spectra indicated that three oligomers were in emeraldine base.(3) The above-prepared aniline oligomers were chemically doped with NPES to obtain self-suspended aniline oligomers. TGA results showed a good coincidence between each doping ratio of the self-suspended aniline oligomers and the corresponding theoretical value. POM images indicated that the three samples were separated, into two phases at nanoscale level and liquid phases were found in local area. Particularly, the self-suspended pentamers exhibited smectic structure, while the trimers and tetramers showed nematic structure. The products featured typical liquid-like manner, and the viscosity (η) was even lower than pure NPES. Amongst three samples, the trimmers exibited the lowest shear storage modulus (G’), shear loss modulus (G") and η. As the degree of polymerization increased, the G’, G" and η of hybrid became more sensitive to temperature variation.(4) PANI was synthesized via solution polymerization, and in situ doped with4-nonylphenol polyoxyethylene ether acetic acid (GAE), NPES and4-nonylphenol polyoxyethylene ether propyl sulfuric acid-20(NPSE) to obtain three self-suspended polyanilines. Both Fourier transform infrared spectra and UV-Vis spectra suggested that PANI had turn from Emeraldine base into Leucoemeraldine base. Transmission electron microscope (TEM) images revealed that dispersion phases of the three products presented as particles, with diameters lower than30nm,5nm and10nm, respectively. POM images presented the liquid crystalline structures in local areas. Interestingly, GAE doped self-suspended polyaniline exhibits unique spindle diffraction structure.(5) The self-suspended polyanilines doped with GAE, NPES and NPSE all exhibited liquid-like rheological behavior and excellent dissolvability in various solvents. The electric conductivity was determined in range of0.1-2S/m. When each possessed the highest doping ratio, PANI-NPSE showed most favorable fluidity and PANI-GAE was the poorest. The flowability of PANI-GAE was most sensitive to temperature, as its viscosity decreased fastest with elevation of the temperature.(6) The PANI-NPES prepared via solution polymerization was further composited with graphite flakes to obtain the PANI/Gr composites. Comparing with that obtained by three-step method, the as-preared PANI/Gr composites showed much lower viscosity and superior electric conductivity. In addition, the PANI/PVDF composites made by blending PANI-GAE, PANI-NPES, PANI-NPSE with PVDF respectively demonstrated remarkable dielectric properties. Especially, the dielectric permittivity of the PANI/PVDF composite prepared from self-suspended polyaniline with7wt.%NPSE reached up to872, while the dielectric loss tan8was as low as0.1.

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