title: The pH-controlled morphology transition of polyaniline from nanofibers to nanospheres.
abstract: To explore the dependences of polyaniline (PANI) morphology on the oxidant and the initial pH value (referred to as 'pH-initial') of the reaction system, a series of oxidative polymerization experiments on aniline using chloroaurate acid (HAuCl4) as the oxidant are carried out in aqueous solutions with different values of pH-initial. The smooth morphology transition of PANI nanostructures from nanofibers to solid and hollow nanospheres can be controlled by simply changing pH-initial for the reaction solution using HAuCl4 as the oxidant. In aqueous solutions with different values of pH-initial, the anilinium ions and neutral aniline molecules coexist in different proportions, leading to different PANI nanostructures under different nucleation mechanisms. In strongly acidic media (pH-initial < 2), the homogeneous nucleation of PANI will result in PANI nanofibers. When pH-initial is raised to 2 or above, the heterogeneous nucleation will lead to solid or hollow PANI nanospheres. The solid PANI nanospheres are obtained in mildly acidic media (pH-initial=2-4) and the diameter decreases as the initial pH value of the reaction solution increases from 2 to 4. However, in weakly acidic and neutral media (pH-initial=5-7), hollow PANI nanospheres are formed and the diameter increases with the increase of pH-initial for the solution from 5 to 7.
authors.affiliation: Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, Institute of Fine Chemicals and Engineering, Henan University, Kaifeng, People's Republic of China. sjiahua@henu.edu.cn
authors.forename: Jiahua
authors.initials: J
authors.lastname: Shi
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wu
authors.forename: Runming
authors.initials: R
authors.lastname: Li
authors.forename: Yinxu
authors.initials: Y
authors.lastname: Zhu
authors.forename: Yujun
authors.initials: Y
authors.lastname: Qin
authors.forename: Congzhen
authors.initials: C
authors.lastname: Qiao
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D017612:Gold Compounds / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D057139:Nanofibers / Q000737:chemistry* / Q000648:ultrastructure; D054118:Nanospheres / Q000737:chemistry* / Q000648:ultrastructure; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction
chemical_list: D000814:Aniline Compounds; D002712:Chlorides; D017612:Gold Compounds; D016877:Oxidants; C416807:polyaniline; C024568:gold tetrachloride, acid