Noriyuki Kuramoto

Processable polyaniline–titanium dioxide nanocomposites: effect of titanium dioxide on the conductivity

‘In-situ’ polymerization was carried out in the presence of anatase titanium dioxide (TiO2) to synthesize polyaniline/TiO2 composite (PANI/TiO2). Emeraldine base form of PANI/TiO2 (PANI(EB)/TiO2) composite was reprotonated with anionic surfactant to prepare homogeneous suspension in m-cresol and chloroform. Conductivity of reprotonated PANI/TiO2 composite film cast from its suspension in m-cresol is higher than that of the film cast from its chloroform suspension due to well-extended conjugation chain of PANI. The anionic surfactant-coated TiO2 suspension and doped PANI solution were combined to form homogeneous suspension and to cast free-standing nanocomposite films with the TiO2 content up to 50 wt.%. Such processable PANI/TiO2 nanocomposite has suitable conductivity (1–10 S/cm) when it is cast from the combined suspension, and it increases after thermal treatment at 80°C for 1 h. It is easy to manipulate the TiO2 content by changing PANI/TiO2 ratio. Also, the nanocomposite film has better quality.

Micellar chemical polymerization of aniline

Abstract Chemical oxidative polymerization of aniline was studied in an aqueous sodium dodecylsulfate (SDS) micellar system. The polymerization proceeded quickly to result in a homogeneous emeraldine-colored dispersion of polyaniline. Absorption spectra of polyaniline dispersion at various pH values showed that the transition from emeraldine salt to emeraldine base form occurred at about pH 7–8 in this anionic micellar system.

Synthesis of processable polyaniline complexed with anionic surfactant and its conducting blends in aqueous and organic system

Processable polyaniline doped and complexed with dodecylbenzenesulfonic acid (PANI/DBSA) was synthesized by one-step micellar chemical oxidative polymerization of aniline in the presence of dodecylbenzenesulfonic acid. PANI/DBSA composite can be redispersed in water after purification at the appropriate content of DBSA. Its particle size at various DBSA/PANI molar ratios prepared by this procedure was investigated by using diluted suspension. Homogeneous suspension in m-cresol was also obtained without precipitation by using PANI/DBSA. Such a processable polyaniline was used to prepare polyaniline composites blended with polyvinyl alcohol (PVA) in water and polyacrylate in organic solvents, respectively. All these two types of composite show high conductivity despite the low weight fractions of polyaniline and its complex with DBSA. Effects of DBSA/PANI molar ratio on conductivity of polyaniline composite, dispersity of polyaniline in aqueous system, and stability of the dispersion were also studied. Increase of DBSA/PANI molar ratio can improve the conductivity of PANI/DBSA composite as well as its complex with PVA due to the increase of dispersity of PANI in the aqueous system in the presence of anionic surfactant.

Property of thermo-sensitive and redox-active poly(N-cyclopropylacrylamide-co-vinylferrocene) and poly(N-isopropylacrylamide-co-vinylferrocene)

Abstract Thermo-sensitive and redox-active polymers were prepared by the copolymerisation of N-cyclopropyl (NCPAM) or N-isopropyl acrylamide (NIPAM) with varying content of vinyl ferrocene (VFc(II)) Aqueous solution of the copolymer showed LCST (lower critical solution temperature) depending on the ferrocene content in copolymers. LCST of the aqueous solution of these copolymers was decreased with increasing ferrocene content in the copolymers. The oxidation of ferrocene has lead to a significant increase in LCST due to a transition from hydrophobic to hydrophilic property of ferrocene moiety in copolymers. The transition could be made reversibly by redox reaction using cerium sulfate as an oxidant and L-ascorbic acid as a reductant. Changes in the cloud point temperature accompanying the transition increased with increasing the amount of ferrocene in copolymer.

Dye‐Sensitized Solar Cell with Single‐Walled Carbon Nanotube Thin Film Prepared by an Electrolytic Micelle Disruption Method as the Counterelectrode

Abstract Several thin films of single‐walled carbon nanotube (SWCNT) were prepared on ITO glasses by electrolytic micelle disruption methods using surfactants bearing a ferrocenyl moiety (1a and 1b). Surfactant 1a has a polyethylene glycol unit as the hydrophilic moiety, while surfactant 1b has an ammonium salt unit. The surfaces of the resulting films formed by the electrolysis methods were confirmed by SEM and AFM measurements, and then these images clearly exhibited that the entire surface of the ITO glass was uniformly covered with SWCNT. The thicknesses of the resulting films were estimated by the SEM images of cross‐sections of the film. For example, the thickness of the film formed by the electrolysis for 12 hours was ca. 4500 Å. Besides the SEM images of the cross‐sections of the resulting films, the UV‐Vis spectroscopy showed clearly that the film thickness increased with electrolysis time. The photovoltaic performance of dye‐sensitized solar cells (DSCs) using the resulting thin films as a counterelectrode material instead of a common platinized counterelectrode was investigated. As a result, the highest solar‐to‐electric energy conversion efficiency among the present investigations was found to be obtained in the case with the thin film formed by the electrolysis with surfactant 1a for 36 hours.

The electrorheological property of a polyaniline-coated copolystyrene particle suspension

Polyaniline-coated copoly (styrene styrenesulphonate) (PSS) particles were prepared by oxidative polymerization of aniline hydrochloride using ammonium persulphate in the presence of anionic PSS particles. Polyanilinecoated PSS particles were found to be higher dispersibility than polyaniline itself in an organic solvent. A suspension of polyanilinecoated PSS particle in silicone oil was found to exhibit high performance at higher temperature without the necessity for water.

Chemical oxidative polymerization of dodecylbenzenesulfonic acid aniline salt in chloroform

Polymerizations of dodecylbenzenesulfonic acid aniline salt (DBSAn) in chloroform using various electron acceptors were studied as a function of polymer yield and conductivity. Dichlorodicyanobenzoquinone (DDQ) is an effective oxidant for the polymerization of DBSAn to yield sufficient amount of polyaniline. Suspension polymerization of DBSAn in chloroform with a small amount of water containing ammonium persulfate (APS) as an oxidant was found to yield a homogeneous transparent and green-black suspension containing polyaniline. Polyaniline was found to exhibit strong solvatochromism in aqueous and chloroform solutions.

Electrorheological property of a polyaniline-coated silica suspension

Abstract Silica particles, whose surfaces were completely covered with polyaniline, were prepared by oxidative polymerization of aniline with ammonium persulphate in the presence of silica particles. The electrorheological property of a suspension of polyaniline-coated silica particles dispersed in silicone oil was found to exhibit a high performance even at high temperatures.

Morphology and growth rate of polyaniline films modified by surfactants and polyelectrolytes

Abstract The rate of electropolymerization of aniline can be significantly accelerated by the addition of small amounts of bifunctional species, polyelectrolytes or surfactants to the monomer solution. In the first case, using para-phenylene diamine (PPDA) for example, the morphology of the polyaniline (PANI) film is densely branched and fibrous. In the latter cases, the mechanism of growth enhancement appears to be quite different, controlled by physical rather than chemical processes. Scanning electron micrographs reveal that the typical fibrous PANI morphology is suppressed and that the granular structure of the initial nucleation is maintained. Cyclic voltammetry confirms that these modified aniline polymers still demonstrate the electrochemical behavior characteristic of pure PANI. Elemental analysis by X-ray photoelectron spectroscopy (XPS) shows that, based on sulfur-to-nitrogen (S/N) ratios, some of the polyelectrolyte or surfactant additive is incorporated into the polymer surface depending on the initial relative concentrations. A model of the effect of polyelectrolyte or surfactant during the electropolymerization of aniline is presented.

Template synthesis of polyaniline in the presence of phosphomannan

Abstract The synthesis of a water-soluble and conducting polyaniline (PANI)–phosphomannan (PMa) complex is presented. Chemical polymerization of aniline was carried out in the presence of PMa, a novel polymeric phosphoric acid and a kind of biomaterial. It was found that the extent of polymerization was affected greatly by initial molar ratio of aniline to PMa in reaction media. A water-soluble and conducting PANI–PMa complex has been obtained under suitable conditions and it exhibited a maximum conductivity by appropriate control of molar ratio of aniline to PMa. The synthesized PANI was characterized by UV–VIS, Fourier transform infrared spectrometer (FT-IR), thermogravimetric analysis (TGA) and inherent viscosity. TGA showed that PANI–PMa complex has highly thermal stability, which was also confirmed by conductivity measurement after exposing the casting films at high temperature.