Li Xin-Gui, Li Ang, Huang Mei-Rong
Institute of Materials Chemistry, College of Materials Science & Engineering, Tongji University, 1239 Si-Ping Road, Shanghai, China.
Chemistry. 2008;14(33):10309-17. doi: 10.1002/chem.200801025.
Chemical oxidative polymerization at 15 degrees C was used for the simple and productive synthesis of polyaniline (PAN) nanosticks. The effect of polymerization media on the yield, size, stability, and electrical conductivity of the PAN nanosticks was studied by changing the concentration and nature of the acid medium and oxidant and by introducing organic solvent. Molecular and supramolecular structure, size, and size distribution of the PAN nanosticks were characterized by UV/Vis and IR spectroscopy, X-ray diffraction, laser particle-size analysis, and transmission electron microscopy. Introduction of organic solvent is advantageous for enhancing the yield of PAN nanosticks but disadvantageous for formation of PAN nanosticks with small size and high conductivity. The concentration and nature of the acid medium have a major influence on the polymerization yield and conductivity of the nanosized PAN. The average diameter and length of PAN nanosticks produced with 2 M HNO(3) and 0.5 M H(2)SO(4) as acid media are about 40 and 300 nm, respectively. The PAN nanosticks obtained in an optimal medium (i.e., 2 M HNO(3)) exhibit the highest conductivity of 2.23 S cm(-1) and the highest yield of 80.7 %. A mechanism of formation of nanosticks instead of nanoparticles is proposed. Nanocomposite films of the PAN nanosticks with poly(vinyl alcohol) show a low percolation threshold of 0.2 wt %, at which the film retains almost the same transparency and strength as pure poly(vinyl alcohol) but 262 000 times the conductivity of pure poly(vinyl alcohol) film. The present synthesis of PAN nanosticks requires no external stabilizer and provides a facile and direct route for fabrication of PAN nanosticks with high yield, controllable size, intrinsic self-stability, strong redispersibility, high purity, and optimizable conductivity.
在15摄氏度下进行化学氧化聚合反应，用于简单高效地合成聚苯胺（PAN）纳米棒。通过改变酸性介质和氧化剂的浓度及性质以及引入有机溶剂，研究了聚合介质对PAN纳米棒的产率、尺寸、稳定性和电导率的影响。通过紫外/可见光谱、红外光谱、X射线衍射、激光粒度分析和透射电子显微镜对PAN纳米棒的分子和超分子结构、尺寸及尺寸分布进行了表征。引入有机溶剂有利于提高PAN纳米棒的产率，但不利于形成小尺寸和高电导率的PAN纳米棒。酸性介质的浓度和性质对纳米级PAN的聚合产率和电导率有重大影响。以2 M HNO₃和0.5 M H₂SO₄作为酸性介质制备的PAN纳米棒的平均直径和长度分别约为40纳米和300纳米。在最佳介质（即2 M HNO₃）中获得的PAN纳米棒表现出最高电导率2.23 S cm⁻¹和最高产率80.7%。提出了形成纳米棒而非纳米颗粒的机理。PAN纳米棒与聚乙烯醇的纳米复合膜显示出低至0.2 wt%的渗滤阈值，在此阈值下，该膜保留了与纯聚乙烯醇几乎相同的透明度和强度，但电导率是纯聚乙烯醇膜的262,000倍。目前PAN纳米棒的合成不需要外部稳定剂，为高产率、尺寸可控、具有内在自稳定性、强再分散性、高纯度和可优化电导率的PAN纳米棒的制备提供了一种简便直接的途径。
