Feng'en Chen

Raman spectroscopic studies on the structural changes of electrosynthesized polythiophene films during the heating and cooling processes

Abstract Polythiophene (PT), poly (3-chlorothiophene) and poly (3-methylthiophene) have been electrochemically synthesized by direct oxidative polymerization of corresponding monomers at stainless steel electrode and in boron trifluoride diethyl etherate solution. The as-grown PT films have been peeled off from the electrode surfaces and characterized by resonance Raman spectroscopy in the temperature scale of 78–573 K. During the heating process, the Raman bands related to the oxidized species decreased gradually, mainly due to the effects of oxygen and moisture in air. Finally, the polymers changed into the neutral states and then decomposed. During the cooling process, the polymer chain segments of the neutral species changed from a disordered (coil-like) to an ordered (rod-like) structure and caused the elongation of conjugated chain length. This led to the dramatic decrease of the Raman intensities of the bands related to the neutral species. On the other hand, the Raman intensities of the bands associated with the oxidized species are nearly independent of temperature. This is mainly because the oxidized species have quinoidic structures and their conformation does not change during the cooling process.

Low potential electrochemical polymerization of 3-chlorothiophene in mixed electrolytes of boron trifluoride diethyl etherate and trifluoroacetic acid

Abstract Poly(3-chlorothiophene) (PCT) films were synthesized electrochemically by direct oxidation of 3-chlorothiophene (CT) in mixed electrolytes of boron trifluoride diethyl etherate (BFEE) and trifluroacetic acid (TFA). The oxidation potential of 3-chlorothiophene in pure BFEE was measured to be only 1.54 V versus SCE. This value is much lower than that determined in neutral medium (2.18 V vs. SCE). The addition of TFA to BFEE can further decrease the oxidation potential of the monomer. The oxidation potential of CT in the mixed electrolyte of BFEE containing 30% TFA (by volume) was found to be as low as 1.16 V (vs. SCE). PCT films with the highest quality were obtained from the media of BFEE+10–15% TFA and they were characterized to have about 24–32 repeat units. The doping level and conductivity of PCT films also increased significantly by using the mixed electrolytes.

Doping level change of polythiophene film during its electrochemical growth process

Polythiophene (Pth) films have been electrochemically deposited on mirror-like stainless steel (SS) (or gold) electrode surfaces by direct oxidation of thiophene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.3 V (vs. Ag/AgCl). The Raman spectra of Pth films have been investigated by excitation with a 514, 633 or 785 nm laser beam. The 633 nm laser beam was found to be the best among the three excitation lights tried for studying the doping level change of Pth film. The overall features of 633 nm excited resonance Raman spectra of as-grown Pth films depend strongly on film thickness. Raman and X-ray photoelectron energy spectroscopic (XPS) results and electrochemical studies demonstrated that the doping level of the Pth film increased with the increase of film thickness. Furthermore, successive cyclic voltammetric scanning was found to be a more effective approach than applying a constant positive potential for doping a thin compact conducting polymer film.

Electrochemical fabrication of aligned microtubular heterojunctions of poly(p-phenylene) and polythiophene

Aligned microtubular heterojunctions of poly(p-phenylene) (PPP) and polythiophene (PTh) were fabricated by successive electrochemical oxidations of benzene and thiophene in freshly distilled boron trifluoride–diethyl ether (BFEE) solution and using a microporous alumina membrane with pores of 200 nm diameter as the template. The morphology and chain structure of the microtubular heterojunctions were studied by scanning and transmission electron microscopies and Raman spectroscopy. The current (I)–voltage (V) curves revealed that the aligned microtubular heterojunctions had a better rectification effect than that of the normal PPP/PTh bilayer heterojunction.

Electrochemical polymerization of thianaphthene

Abstract Thianaphthene has been electrochemically polymerized in pure boron trifluoride diethyl etherate (BFEE) solution or in a mixed electrolyte of BFEE and concentrated sulfuric acid (SA). The addition of a certain amount of sulfuric acid into BFEE accelerated the polymerization and also increased the current efficiency of the electrosynthesis. Poly(thianaphthene) (PTN) in the dedoped state is soluble in usual strong polar organic solvents such as dimethyl sulfoxide (DMSO), N , N -dimethylformamide (DMF) and N -methyl pyrrolidinone (NMP). Its structure has been examined by infrared, H 1 -NMR and UV spectra. Fluorescent spectral studies indicate that the polymer is a strong blue light emitter.

Aligned polythiophene coated gold nanowires

Metallic gold (Au) nanowire arrays coated with polythiophene (PTh) films were fabricated by successive electrochemical depositions of PTh and the metal into the pores of a microporous alumina membrane. The diameter of the composite nanowires was 200 nm and that of the Au nanowires was about 100 nm. They are adhered to a thin gold film and aligned in a high density of 10 10 wires / cm 2 . The morphology of the composite nanowires has been characterized by an optical microscope, Raman spectroscopy, scanning and transmission electron microscopies.

Visualization Experimental Study on Starting Process of the Absorber Sphere Pneumatic Conveying

Visualization experiments were conducted in a positive pressure system to investigate the starting process characteristics of the absorber sphere pneumatic conveying. The ambient air was used as the source gas. The absorber sphere was replaced by the glass sphere. Spouted spheres flow was observed at the early stage of the starting process. With the increase of feeder inlet gas flow rate with time after starting the blower, the amount of fluidized spheres in the riser pipe first increased gradually and then decreased to the steady conveying state. The steady conveying was achieved as the feeder inlet gas flow rate was up to the maximum. A peak pressure was observed at the feeder gas inlet. The sphere blown away pressure was approximately 20 kPa higher than the steady conveying pressure. The time lasted for the pressure higher than the steady conveying pressure was about 10 s. The process for spheres blown away at the early stage of the starting process was more difficult than the steady conveying. The pressure increase and the duration characteristics should be taken into account for the blower pressure parameters design in the practical engineering application.

High-quality polyene prepared by liquid/solid two-phase dehydrochlorination of poly(vinyl chloride)

Polyvinyl chloride) (PVC) can be dehydrochlorinated extensively in a liquid/solid two-phase system by the catalyzation of poly(ethylene glycol) (PEG). The product, dehydrochlorinated poly(vinyl chloride) (DPVC), is polyacetylene-like and has the longest polyene sequences so far and a narrow dispersity of polyene sequences according to its FT-infrared and Raman spectra.