Synthesis And Properties Of Nano-Polyaniline

Polyaniline(PAn) is one of the most thoroughly studied conducting polymers because it has excellent environmental stability, particular doping mechanism and good electrochemical properties. The film made by PAn has some miraculous physical and chemical properties ( such as conductivity and electrochromism ,etc.), and could be potentially used in display devices ,secondary battery , gas separation, etc.For PAn , a serious matter in application is its poor processability resulted from its insolubility and infusibility. Nano-conducting polymers has become a focus in recent years , in that nanotechnology unite the polymers' conductivity and the function of nanoparticles ,which will greatly improve the processability of conducting polymers. This article is mainly about the synthesis of nanopolyaniline in a kind of microemulsion consisting four elements: emulsifier, aniline, emulsifier aids and water , in which emulsifier served as dopant , surfactant and the source of proton. Meanwhile, the formation mechanism, mechanical stability and thermal stability of microemulsion were studied in detail.PAn was synthesized under various conditions, and its electrochromism, conductivity and yield were studied. By orthogoral experiments, a better synthetic direction for producing PAn was made as follows: the molar ratio of initiator to monomer (aniline) and that of surfactant to monomer (aniline) are all 1.25; the reaction temperature and reaction time are 10℃ and 3 hours, respectively. It is also found that the dimension of PAn decreases with the increase of the ratio (surfactant to water).The analysis of Atomic Force Microscope(AFM) shows that the average dimension of PAn is about 4～5nm,within the range of 30nm, and the distribution is very narrow and uniform. Compared with non-nanoparticles made from conventional emulsion polymerization, nanopolyaniline made from microemulsion has apparent advantages: more eletrochromic cycles, and conductivity up to 1.19S/cm, which is more than 100 times higher than that of non-nanopolyaniline ; higher solubility in conventional solvent (this provides a possibility to make self-sustained PAn film); X-ray diffraction shows that the crystal of nanopolyaniline is more uniform . Thermal analysis shows that electrochemical property remains still even temperature is up to 160℃～180℃. Ultra-violet spectrum indicates that nanopolyaniline has apparent blue-shift. This makes it possible to prepare transparent composite film. Based on the preparation of nanopolyaniline , transparent composite film was made using poly(vinyl alcohol) and a solution consisting PAn in chloroform , while the solution was made by extraction. The composite film is electrochemically active when temperature is as high as 180℃. The scanning electron microscope (SEM) of the composite film shows that when percentage of PAn is low, electrochemical activity is obtained by the nanoparticles' quantum tunnel effect; when percentage of PAn is higher, the film is electrochemically active because of the crosslinking of PAn.