Study of free volume and crystallinity in polybithiophene and poly(3-methylthiophene)

Compressed pellets of partly crystalline, chemically synthesized, doped (Cl^? and FeCl) polybithiophene (PBTd), poly(3-methylthiophene) (P3MTd), and their neutral (dedoped) forms (PBTn and P3MTn) were studied by wide-angle x-ray diffraction and positron annihilation lifetime spectroscopy. As synthesized, PBTd and P3MTd polymers have a helical syn conformation they crystallize in the hexagonal system. On dedoping, PBT macromolecules change their helical syn conformation in a rodlike anti conformation and crystallize in the orthorhombic or monoclinic system, whereas P3MT macromolecules retain their helical syn conformation. Chemical doping–dedoping cycles lead to amorphous PBT and P3MT in either doped or dedoped states. The P3MT helical macromolecule behaves like a spiral spring; by doping, it becomes axially compressed. The unit-cell volume of P3MTd is smaller than that of P3MTn. The positron lifetime spectra for all polymers were resolved, without constraint, into three components. The τ₁ lifetime is attributed to free-positron annihilation events, the τ₂ lifetime to positrons annihilating trapped in voids, and the τ₃ lifetime to positrons annihilating as o-Ps trapped in cavities located inside the polymer grains for P3MTn and at the surface of the grains for PBTd, PBTn, and P3MTd. Most positrons annihilate when trapped in voids, both in doped and dedoped PBT and P3MT. The doping apparently increases the concentration of the voids and their mean diameter in P3MT, and probably also in PBT. Cavities anchored in the bulk are produced by dedoping. © 1993 John Wiley & Sons, Inc.     

Cathodic doping of thin-layered composites. Formed by electroactive polymers and rubbed single-walled carbon nanotubes

A simple method of electrostatic rubbing is developed for the application of single-walled carbon nanotubes (SWNT) to solid substrates. The method is applicable both to conducting materials (for example, glassy carbon) and insulators (for example, Teflon). The surface development of the obtained coatings is comparable to the bodies of multi-walled carbon nanotubes, which are grown on the TiN substrates. The possibility of cathodic doping of electron-conducting polybithiophene polymer and poly-o-phenylenediamine redox polymer on the substrates with SWNT is shown. The presence of nanotubes accelerates anodic synthesis of test polymers and improves the reversibility of their cathodic doping, the electrode surface development being the main factor.     

Electrochemical properties of thin-layered composites formed by carbon nanotubes and polybithiophene

Redox behavior of thin films of polybithiophene deposited on substrates of conducting glass and single- or multi-walled carbon nanotubes is studied at positive potentials in a 0.1 M (C₄H₉)₄NBF₄ solution in acetonitrile. The polymers formal doping-undoping potentials are nearly the same for all substrates, which points to the absence of any marked donor-acceptor interaction between nanotubes and polybithiophene. Some polybithiophene electrochemical characteristics (reversibility, doping degree) are improved when deposited onto nanotubes, probably due to the developed surface of the electrode based on carbon nanotubes.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 501–509.Original Russian Text Copyright © 2005 by Ovsyannikova, Efimov, Moravsky, Loutfy, Krinichnaya, Alpatova.     

Polybithiophene Heterogeneity: A Differential Cyclic Voltabsorptometry Study

The redox behavior of polybithiophene in 0.1 M Bu₄NBF₄ solutions in acetonitrile is studied using cyclic voltammetry, potentiostatic spectroelectrochemical measurements, and differential cyclic voltabsorptometry. Comparing differential cyclic voltabsorptograms, obtained at wavelengths of 420, 475, and 520 nm for the undoped state and 720, 850, and 1050 nm for the doped state, with the cyclic voltammetry data reveals the polymer heterogeneity. The heterogeneity of the undoped polymer is ascribed to the formation of polymer chains of different lengths during the polybithiophene synthesis. The heterogeneity of the doped polymer is attributed to the existence of two types of an oxidized state. Both states presumably form as the result of the occurrence of two parallel processes. The first oxidized state is probably connected with the formation of a strong complex (associate) of positively charged fragments of a polymer chain with the dopant anion, while the second oxidized state is caused by a weak interaction between the dopant and the doped polymer.     

Electrochemical and chemical modification of poly-o-phenylenediamine redox polymer

Various methods for modification of poly-o-phenylenediamine (PPD) redox polymer with polyaniline (PANI) electron-conducting polymer, ReO ₄ ⁻ and [SiMo₁₂O₄₀]⁴⁻ anions, and palladium clusters are compared. Participation of anions is proven in the processes of PPD synthesis and redox transformations. Formation mechanisms and properties of composites consisting of a redox polymer and electron-conducting polymer and those of two different electron-conducting polymers are compared for example of PPD-PANI and ethylene-dioxythiophene-polybithiophene. A comparison of these systems shows the main change in the potential drop to take place at the metal/polymer interface for a redox polymer and at the polymer/solution interface, for an electron-conducting polymer. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1409–1416. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The article was translated by the authors.     

Surface spectroscopic characterization of advanced polymer materials

The potential of a complementary use of X-ray photoelectron spectroscopy and static ToF-SIMS has been exploited with reference to the characterization of electron conducting polymers (polybithiophene) electrochemically synthetized. Particular attention has been focused on the problem of material stability under electrochemical switching.A coherent picture could be drawn showing that irreversible modifications of the surface chemistry occur, strongly dependent on the dryness of the solvent; moreover, the pathway of doping-undoping process can vary noticeably in dependence on the experimental conditions.