Preparation of polyaniline nanofibers via a novel interfacial polymerization method
Introduction
In recent years, polyaniline (PANI) nanofibers have received much attention owning to their superior properties to the conventional bulk PANI materials [1], [2], [3]. For example, compared to the bulk PANI materials, PANI nanofibers have enhanced water processibility [4]. Meanwhile, the PANI nanofibers show improved sensitivity and time response when they are exposed to chemical vapors because they embody porous characteristic and large surface area. Besides, PANI nanofibers show unique advantages in other fields, including electric devices and flash welding [5]. Aiming to obtain PANI nanofibers with high quality, “structural directing agents” are often utilized to guide for the formation of nanofibers, such as surfactants, polyelectrolytes, nanowire seeds and aniline oligomers [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Under these conditions, the structural directing agents act as templates during the polymerization of aniline in aqueous solutions. Epstein et al. found dilute polymerization of aniline is favorable for production of nanofibrous structures [17], [18]. In the last 2 years, the preparation of PANI nanofibers has received great development owning to the excellent work by Huang and Kaner et al. [5], [19], [20], [21], [22], [23]. They found it is the nature for PANI to form nanofibrillar morphology. In order to obtain pure PANI nanofibers, the secondary growth of the initially formed nanofibers must be suppressed. They have developed two effective methods to suppress the secondary growth of the nanofibers, e.g., interfacial polymerization and rapidly mixing reaction. In the former one, the aniline is polymerized at the interface between two immiscible liquids, where the newly formed PANI nanofibers diffuse away from the interface to the aqueous solution because of their hydrophilicity. This makes more reaction sites available at the interface and avoids further growth of the PANI nanofibers. During the rapidly mixing reaction, the oxidant is consumed rapidly and depleted after the formation of the nanofibers, which also suppresses the secondary growth of the PANI. However, in the former method, nearly the same volume of organic solvent to water was used, and the solvents immiscible to water are typically toxic. Here, we provided a novel interfacial polymerization method by using much less organic solvent. In our experiment, the aniline was dissolved in small amount of xylene and directly added into the aqueous solution of the oxidant to induce the polymerization under stirring. Owning to the stirring conditions, the xylene was dispersed into liquid drops in the reaction system, which provided relatively large interfacial area for the polymerization of aniline. Different preparation conditions, including the xylene usage, reaction time and stirring rate have been carried out in order to investigate their influence on the morphology, structure, water-dispersity and conductivity of the resulting polymer.
Section snippets
Materials
Aniline was distilled under vacuum before use and other regents were used as received.
Synthesis of PANI nanofibers
A typical experiment was carried out as follows: 0.47 g of aniline was dissolved in xylene. Then the above solution was dropped into the hydrochloride solution containing 1.14 g of ammonium persulfate (APS) under stirring. The mixture was stirred at room temperature for a period of time. The resulting precipitate was collected by filter. After the product was washed by deionized water and ethanol continuously,
Morphology
We consider the formation process of the PANI nanofibers in our experiment is similar to that Huang has reported [20]; however, the differences between the two must be noted. In Huang's experiment, the polymerization was carried out without any stirring and the volumes of the organic and aqueous phases were almost equal to each other. On the contrary, we only used ca. 1 mL of organic solvent (typically they are toxic) for the polymerization, which is only 1/20 of the amount Huang has used and
Conclusions
PANI nanofibers were successfully prepared by a novel interfacial polymerization method. The aniline was dissolved in xylene and directly added into the aqueous solution of the oxidant under stirring. Because of the immiscibility of xylene to water, the xylene was dispersed into liquid drops in the reaction system under the stirring condition, which greatly improved the interfacial area for the polymerization of aniline. The xylene usage, reaction time and stirring rate were changed to
Acknowledgments
This work was supported by Science Foundation for Young Teachers of Northeast Normal University (No. 20060312). Many thanks are due to Mr. Chao Zhou (Research master candidate of Nanjing University of Science and Technology) for rectifying this paper in English and his suggestions.
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