Wide-range regulation of polyaniline conduction by interphase doping of a polyaniline film

The not-sufficient-enough conductance of semioxidized protonated polyaniline (PANI) is usually attributed to the presence of ordered quasi-metallic domains surrounded by a poorly conducting amorphous phase. The paper presents experimental results testifying to the existence, in semioxidized PANI, of multilevel redox heterogeneity that crucially effects the conductance magnitude in view of specific topology at which higher-oxidized (conducting) domains are surrounded by less oxidized (poorly conducting) domains and because the PANI conduction is extremely sensitive to the oxidation degree. It is shown experimentally that the interphase doping with metals and degenerate semiconductors of a semioxidized salt of PANI and poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (PAMPSA) with a 1: 2 ratio between PANI and PAMPSA raises the PANI-PAMPSA conductivity by 3–8 orders of magnitude due to the formation near the interface of thin layers whose conductance depends on the work function of the material in contact with PANI-PAMPSA and in extreme cases substantially exceeds the conductance of gold and copper at room temperature.     

New carbazole-containing polyphenylquinoxalines: Synthesis,photophysical, and electroluminescent properties

New carbazole-containing polyphenylquinoxalines combining the electron-transport behavior of quinoxaline with hole-transport and electroluminescent properties of carbazole have been synthesized. The polymers show solubility in organic solvents. Their glass transition temperatures range from 315 to 370°C, and temperatures corresponding to 10% weight loss vary from 510 to 560°C (in air). It has been demonstrated that these polymers exhibit electroluminescent behavior in the 450–750 nm spectral region and offer promise as emitting and electron-hole transport materials for polymeric light-emitting diodes.     

Electrophosphorescence of aromatic polyimides doped with platinum porphyrins

The mechanism of electroluminescence in polymeric thin-layer devices based on aromatic polyimides and various molecular complexes of Pt porphyrins as heavy-atom-containing luminophores was studied. On the basis of spectral and electron-hole transport properties of aromatic polyimides and Pt porphyrins, as well as the current concepts adopted in polymer photonics, the processes of singlet-singlet and triplet-triplet energy transfer in the examined single-layer systems aromatic PI-Pt porphyrin with a high electrophosphorescence quantum yield exceeding 2% are discussed.     

Infrared photorefractive composites based on polyvinylcarbazole and carbon nanotubes

Photorefractive materials based on unplasticized polymers that have a high glass-transition temperature and the frozen random orientation of chromophores were prepared by layer casting. Under these conditions, only the third-order susceptibility has a nonzero value, increasing with an increase in the conjugation-chain length and reaching considerable values in the case of nanosized molecules, such as single-wall carbon nanotubes (SWNTs). In SWNT-containing polyvinylcarbazole, the photoelectric sensitivity and photorefractive characteristics were measured at 1064 nm. Using electric-field induced second-harmonic generation, the third-order susceptibility was estimated. In a composite containing 0.26 wt % SWNT, the diffraction grating is displaced by 5° relative to the interference pattern, the result that is presumably due to the close mobility of unlike charge carriers. Therefore, the beam-coupling gain coefficient Γ and the net gain Γ-α have low values, which are 53 and 42 cm^?1, respectively, at 115 V/μm.     

On the Role Played by Dimers of Radical Cations in the Process of Electrochemical Oxidation–Reduction of Polyaniline: The Data that Were Obtained Using the Method of Cyclic Voltabsorptometry in the Presence of Counteranions of a Diverse Nature

The electrochemical oxidation–reduction of films of polyaniline is studied in the presence of various counteranions. The differential cyclic voltabsorptometric (DCVA) curves (dA/dt relative to potential, where A is the optical absorption) are recorded at characteristic wavelengths corresponding to individual spectrum components previously isolated with the Alentsev–Fok method. The DCVA curves for aqueous solutions of HCl, HClO₄, and H₂SO₄ at different potential scan rates are compared to traditional cyclic voltammograms. For the DCVA curves obtained at 665 nm discovered is one broad peak of dA/dt in the region of potentials between the first and second stages of polyaniline oxidation (0.6 V vs. Ag/AgCl). An assumption is made about a chemical nature of the process of generation of absorption in this spectral region, which, more likely than not, is connected with the emergence of dimers of radical cations of polyaniline. It is discovered that the electrochemical processes in the region of potentials that correspond to the first stage of oxidation give rise to variations in the absorption inside several regions of spectrum: 435 nm (radical cations) and 755 nm (localized polarons). An assumption is made that the first peak of the current corresponds to several successive processes that occur in a polyaniline molecule in the course of oxidation as well as to the existence of heterogeneous regions where the generation of localized polarons proceeds at different rates.     

The third-order nonlinear optical properties in polymer ferroelectrics

The third-order susceptibility of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer are analyzed by using the z-scan technique with a nanosecond laser as an excitation source. It is established that optical transmittance of the VDF-TrFE samples decreases after their polarization in an electric field.     

Effect of interface in bilayer polydiphenylenephthalide film on electron transport

The results of studies of multilayer film structures based on a wide-gap polymer using the time of flight technique are shown. Experimental data showed that transport of charge carriers depends strongly on the presence of a polymer/polymer interface. The possibility is shown of increasing the threshold thickness of the experimental structure, in which effects of switching to a highly conducting state induced by uniaxial mechanical pressure are also found. Preliminary interpretation of the obtained data is performed.     

Photorefractive properties of a nanocomposite based on a ferroelectric polymer

The photorefractive effect is demonstrated for the first time for the composite consisting of a ferroelectric material (polyvinylidenefluoride-trifluoroethylene) and single-walled carbon nanotubes that serve as nonlinear optical chromophores and, simultaneously, spectral sensitizers for the laser radiation with a wavelength of 1064 nm. It is demonstrated that the internal field in the ferroelectric material makes it possible to measure the photorefractive effect in the absence of the external field.     

Photorefractive polymer composites for the IR region based on carbon nanotubes

The photorefractive properties of polymer composites based on aromatic polyimide and single-wall carbon nanotubes are studied using radiation at a wavelength of 1064 nm. It is found that the nanotubes possess photoelectric sensitivity in this spectral region and that the kinetic photorefractive characteristics of the polymer composites are entirely determined by the photogeneration and charge transport characteristics of the layers. The two-beam gain coefficient of the signal beam measured for a composite consisting of aromatic polyimide and 0.25 wt % of single-wall carbon nanotubes in a constant electric field E₀ = 79 V/μm is equal to 84 cm^?1 and exceeds the optical absorption coefficient by 59 cm^?1. The refractive index modulation is equal to Δn = 0.004 at E₀ = 54 V/μm.