| Layer-by-layer self-assembly (LBL-SA) technique is a simple, rapid and effective method to prepare ultra-thin sensitive films. The fabricated films comprise a variety of materials in accordance to the requirement and can be constructed on any shape and size of substrates by different processing parameters. The average thickness and surface function of each monolayer can be accurately controlled and tuned. Polyaniline (PANI) is one of the most potential conductive polymers, but the further applications of polyaniline are restricted by the low solubility and high melting temperature of polyaniline, and long response time and high threshold detection limit of polyaniline films. In this dissertation, we focus on the investigation of polyaniline films that were fabricated from aniline (AN) monomers by in situ polymerization, self-acid-doping and layer-by-layer self-assembly through the electrostatic force or hydrogen bonding. Formation mechanism of the PANI self-assembled films was proposed. The detection of NH3 using as prepared PANI films was also studied. Furthermore, the structure of the PANI films was tuned by acid doping or dedoping. The humidity resistance and the sensitivity to chemical warfare agents (CWAs) simulants of the tuned films were also investigated.Self-assembled LBL polyaniline films were prepared from aniline monomers by in situ polymerization and the mechanism of film formation was discussed. It was proposed that the self-assembly of polyaniline occurred through the quick absorption of aniline monomer cations or aniline monomer cation radicals on the glass surfaces by electrostatic attractions to form homogeneous polymerization centers, then increased gradually by the way of upright to the glass supports for extensity, leading to the polyaniline chain growth. The polyaniline was doped under acidic condition to absorb anionic polyelectrolyte, such as sodium polystyrene sulfonate (PSS) based on the electrostatic force, or to adsorb polymer based on hydrogen-bonding interactions, for example Polyvinyl Alcohol (PVA), and then recycled to fabricate (PSS/PANI)n or (PVA/PANI)n self-assembled multilayer films.Based on the formation mechanism of the film, stable, porous, and amorphous nano-structured (PSS/PANI)n multilayer films with adjustable structure and properties were prepared. The deposition conditions for the fabrication of 30 - 100 nm PSS / PANI films were optimized. The optimum deposition conditions are: the concentration of PSS solution is 0.001 - 0.02 mol·L-1, the molar ratio of oxidant to aniline (nASPS : nAn) is 0.8 -1.2, the oxidant APS is added into the aniline solution at different polymerization stages, and the deposition time should be at least 10 min. Under this optimum deposition conditions, (PSS/PANI)n multilayer films with equal thickness of each layer and good conductivity were prepared by adjusting the concentration of aniline solution and the in situ polymerization time.Based on the principle that resistance of (PSS/PANI)n self-assembled films increases due to the chemical absorption of NH3, its sensitivity to NH3 was investigated. Results show that these films exhibit quick response, low detecting limit, high sensitivity, and good selectivity. When the concentration of NH3 is 0.1 mg/m3 , the relative sensitivity of this film is 63.47 % and the response time is only 39 s. This established foundations for the preparation of polyaniline NH3 sensor with high sensitivity and good selectivity.The humidity resistance of PSS/PANI self-assembled film was improved by adjusting its structure through redoping. Sensing ability of PSS/PANI self-assembled film with different doping/dedoping structure to DMMP and CEES was investigated. Results demonstrate that the gas sensitivity of PSS/PANI self-assembled film is affected by the size of dopant counterions. Gas sensitivity of self-assembled film increases with increasing size of dopant counterions. It is found that sensing ability of PSS/PANI self-assembled film to DMMP increases significantly by redoping/dedoping EB-PSS/PANI film with sarin acid that has similar structure with DMMP.Interface construction and preparation of new in situ polymerized polyaniline layer-by-layer self assembled films were also investigated. (PANI/PVA)n films were prepared from aniline monomers by in situ polymerization, and layer-by-layer self-assembly through the hydrogen bond; (PSS/POT)n films were prepared from o-methylaniline monomers by in situ polymerization, and layer-by-layer self-assembly through the electronstatic bond. All results suggested that uniform thin composite film containing PANI, PSS, PVA, or POT could be fabricated using this simple process and the order of these polymers could be changed as required. Consequently, it is possible to increase the sensitivity of polyaniline self-assembled film to CWAs through adjusting the structure of the films.
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