With an average diameter of 150−340 nm and a conductivity of 10-1−100 S/cm, nanostructures (e.g., nanotubes or nanorods) of polyaniline (PANI) were synthesized by a self-assembly method in the presence of inorganic acids (e.g., HCl, H2SO4, HBF4, and H3PO4) as dopants. It was found that the morphology, size, and electrical properties of the resulting nanostructures depended on the dopant structures and the reaction conditions. In particular, all these PANI nanostuctures showed hydrophilic features, and the contact angles with water were measured to be about 27−40° depending on the dopant. The FTIR spectrum, UV−vis absorption spectrum, XPS, and X-ray diffraction were used to characterize the molecular structures of the nanostructures. It was found that their main chain structure and electric structure were identical to those of the emeraldine salt form of PANI. The micelles formed by anilinium cations act as the template like in the formation of PANI nanostructures.

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By simply changing the molar ratio of the dopant to monomer, the morphology of salicylic acid (SA)‐doped polyaniline (PANI) can be changed from one‐dimensional nanotubes (∼ 109–150 nm in diameter) to three‐dimensional hollow microspheres (∼ 1.5–3.1 μm in diameter) via a self‐assembly process. Freeze–fracture electron microscopy (FFEM) proved that hollow spherical micelles composed of SA/aniline act as templates in the formation of either nanotubes or hollow spheres. FTIR and X‐ray diffraction measurements suggest that the hydrogen bond of the –OH group of SA with the amine group of PANI might be a driving force for self‐assembling hollow microspheres, while the hydrogen bond through hydrogen and oxygen of the adjacent SA doped on the polymer chains results in short‐range order of the counter‐ions along the polymer chain in the nanotubes.

Conducting polymer nanostructures have recently received special attention in nanoscience and nanotechnology because of their highly π‐conjugated polymeric chains and metal‐like conductivity, such that they can be regarded not only as excellent molecular wires, but also as basic units for the formation of nanodevices. Although various approaches, such as hard‐template methods, soft‐template methods, electrospinning technology, and so on are widely employed to synthesize or fabricate conducting polymer nanostructures and their composite nanostructures, each of the currently used methods possess disadvantages. Therefore, finding a facile, efficient, and controlled method of forming conducting polymer nanostructures is desirable. Similar to other nanomaterials, the effect of size (in these cases 1–100 nm) on the properties of the conducting polymer nanostructures must be considered. Electrical measurements of single nanotubes or nanowires are desirable in order to be able to understand the pure electrical properties of conducting polymer nanostructures. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in technological applications because of the unique properties arising from their nanometer‐scaled size: high conductivity, large surface area, and light weight. Thus, it is also desirable to develop promising applications for conducting polymer nanostructures. In accordance with the issues described above, our research focuses on a new synthesis method to form conducting polymer nanostructures and on the related formation mechanism of the resultant nanostructures. The electrical and transport properties of single nanotubes of conducting polymer, measured by a four‐probe method, and promising applications of such template‐free‐synthesized conducting polymer nanostructures as new microwave absorbing materials and sensors guided by a reversible wettability are also of interest. This article reports some of our main results and reviews some important contributions of others.

Hollow polyaniline microspheres have been synthesized from a monomeric aniline‐based template, which makes template removal unnecessary. The template for the microstructures is an aniline emulsion with β‐naphthalenesulfonic acid (NSA) as dopant, and ammonium persulfate (APS) as oxidizer. The Figure is a TEM image of polyaniline/NSA spheres obtained from 0.2 M aniline at an NSA/aniline/APS ratio of 1:4:4.

Recently, micro-or nanoscaled hollow spheres of conducting polymers have attracted great attention because of their potential use in encapsulation applications, confined reaction vessels, controlled release and delivery, separation systems, and biosensors.[1] Usually, hollow spheres are prepared from spherical-particle templates, such as silica colloids, [1a,2] polystyrene beads, [1d,3] inorganic particles, [1b,1c,4] followed by the removal of the sacrificial core through calcination and solvent etching. Clearly, in this template method, the complex procedures involved in preparing and removing the templates lead to poor reproducibility and make it rather difficult to retain the ordered structure after template removal. Recently, our group reported that hollow microspheres of polyaniline (PANI) could be prepared by a self-assembled method using a dopant of either salicylic acid (SA) [5a] or b-naphthalene sulfonic acid (b-NSA) at -10°C.[5b] Moreover, hollow polypyrrole (PPy) capsules in the presence of chitosan have also been reported by using a facile one-step pathway.[6] Although various methods have been reported to prepare hollow spheres of conducting polymers, control of the morphology and properties of the prepared conducting polymers using a simple and effective method still remains scientifically challenging. In practical applications, moreover, the main problems are shown as follows: the conductivity of conducting polymers is easily influenced by humidity and dust from their surroundings, and the encapsulated materials are easily dissolved or contaminated by the immerged water. Superhydrophobic surfaces, characterized by a water contact angle (CA) higher than 150°, are arousing much interest because of their high water repellency and practical applications such as in the prevention of adhesion of snow to antennas and windows, self-cleaning traffic indicators, metal refining, stain-resistant textiles. [7,8] Therefore, the combination of micro-and nanostructured conducting polymers with a superhydrophobic function has became an interesting object in materials science. Super water-repellent poly(alkylpyrrole) films, super water-and oil-repellent polythiophene films, reversible switching of polypyrrole films from superhydrophobic to superhydrophilic, and superhydrophobic PANI films have all been recently reported. [9,10] To the best of our knowledge, however, previous results mainly focus on films of superhydrophobicity. Herein, we report on conductive and superhydrophobic rambutan-like hollow spheres of PANI prepared by a self-assembly method in the presence of perfluorooctane sulfonic acid (PFOSA), which served as dopant, soft template, and induced superhydrophobicity at the same time. The resulting hollow PANI spheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, and X-ray photoelectron spectroscopy (XPS). Water contact angle and conductivity measurements were also conducted. In ...

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