Polypyrrole nanoparticles and dye absorption properties

Polypyrrole (PPy) nanoparticles were prepared by using microemulsion polymerization processes at 3 °C. Particle characterization was performed by using FTIR, elementary analysis, UV–vis spectra and scanning electron microscope (SEM). The size of the nanoparticles varied from about 50 to 100 to 100 to 200 nm with the change in concentration of surfactant from 0.8 to 0.44 M. Polypyrrole nanoparticles were dedoped by a 10% NaOH solution, followed by a redoping process using a nuclear fast red kernechtrot dye, which has a sulfonate group. Dedoping changed the optical absorption properties of the nanoparticles.     

Conducting organic polymers with electroactive dopants. Synthesis and electrochemical properties of hexacyanoferrate-doped polypyrrole

A systematic study of the synthesis of heacyanoferrate-doped polypyrrole (PPy/HCF) is reported. In addition to the electrochemical growth of films, we report three different modifications of a novel chemical synthesis for the preparation of bulk powdered materials by oxidative polymerization of pyrrole by the acid derivative of HCF. The effect of temperature and duration of the reaction, doping level and aging of the materials obtained on their conductivity has been systematically studied. Higher conductivities are obtained for materials prepared at lower temperatures (0°C). This is associated to a higher content of the doping HCF anion for these lower temperature materials. With time the conductivity of all samples decreases proportionally to the corresponding initial values. Finally, we report the electrochemical properties of these hybrid materials, the cyclic voltammograms of chemical and electrochemical derivatives and their intercalation behavior, which shows a deintercalation of the electroactive HCF anion in aqueous electrolytes but not in organic (propylene carbonate, dimethoxyethane) media.     

Anion effects on conductivity of isomorphous polypyrrole. Charge pinning by nucleophilic anions

Anion dependence of conductivity in well-ordered polypyrrole tosylate deposits was determined by anion exchange in aqueous medium with several inorganic (NO₃⁻, ClO₄⁻, F⁻, Cl⁻, Br⁻, BF₄⁻, HSO₄⁻, OH⁻) and organic (CF₃COO⁻, CH₃COO⁻, CH₃CH₂COO⁻, PhCOO⁻, PhO⁻, p-CH₃---C₆H₄---SO₃⁻) anions. Conductivity was found to be high (80–100 S cm⁻¹) and almost independent of anion size and (for anions of strong acids) of anion type, but it decreased with increasing anion basicity (70 S cm⁻¹ for carboxylate, 25 S cm⁻¹ for phenoxide and 3 × 10⁻² S cm⁻¹ for hydroxide anion). Quenching of conductivity by nucleophilic anions is explained by pinning of positive charges in the polypyrrole backbone with a pinning energy as high as 0.4 eV for OH⁻, as determined by E⁰ shifts in the cyclic voltammograms of the polymer.     

Electrical and optical properties of carbon nanotube/polypyrrole addressable intra-connects

Carbon nanotube (CNT) intra-connects (bridges spanning across in-plane electrodes) were electroplated with polypyrrole (PPy), an electrically conductive polymer (ECP). Sharp metal electrodes initiated the CNT growth at pre-selected locations. The CNT bridge was then used as an electrode for conductive polymer electro-deposition. The samples were characterized by Raman spectroscopy and current–voltage measurements. We found that current–gate voltage (I_ds–V_gs) characteristics changed dramatically for the electroplated structures when the polymer exceeded a threshold thickness, in the order of 80 nm. In addition, the CNT/PPy structures exhibited large sensitivity to UV radiation: the current substantially reduced upon irradiation with moderate UV intensity values.     

The influence of size effect of conductivity on the microwave absorption properties of thin Al films

采用中频磁控溅射法制备不同厚度的Al膜。利用直线型四探针法测量不同厚度Al膜的电导率,研究薄膜直流电导率随厚度的变化关系（尺寸效应）;并利用网络矢量分析仪测量Al膜与FR4-epoxy环氧树脂玻璃板复合结构微波吸收率,研究电导率尺寸效应对Al膜微波吸收性能的影响。实验结果表明：薄膜厚度对金属Al膜的电导率产生主要影响;在Al膜和FR4-epoxy环氧树脂玻璃板复合结构中,Al膜电导率变化对复合结构的最大吸收峰值以及吸收峰值对应的Al膜厚度会产生显著影响。实验结果利用传输矩阵方法计算得到了验证。     

The influence of quantum size effects on optical absorption of metallic composite

The optical properties of an ensemble of metallic nanoparticles in an insulating matrix have been studied in terms of the classical Maxwell Garnett theory. To estimate the quantum effects, the analytical expression for the dielectric function of a metallic particle in the form of a parallelepiped has been used that was derived within the model of free electrons and potential well of infinite depth. The absorption coefficient has been calculated for composites with particles of various metals in various matrices.     

Effects of dopants and polymer structures on electrical conductivity of organosilicon polymers

A series of organosilicon polymers comprising disilanylene-phenylene, disilanylene-ethynylene and disilanylene-(bisethynylene-phenylene) chains carrying dibutyl or phenyl and methyl groups as side chains, and polysilanes carrying alkyl, aromatic or heteroaromatic side chains were synthesized. The electrical conductivities of their polymers doped with electron acceptors such as I₂, FeCl₃ and SbF₅ were measured by using vapor-phase doping. The electrical conductivities of organosilicon polymers doped with I₂ showed a good correlation with the ionization potentials of the original polymers. In contrast, in the case of SbF₅ doping, the degradation of polymers occurred and every polymer gave the same order of conductivity, 10⁻⁴−10⁻³ S/cm. The polymers carrying heteroaromatic substituents gave the higher conductivity by doping with I₂, while in the case of the polymers carrying phenyl groups, the conductivity was enhanced by doping with FeCl₃.     

Pressure dependence of electrical conductivity in polypyrrole

The electrical conductivity as a function of pressure to about 1.1 GPa is determined for p-toluenesulphonate-doped polypyrrole at two different doping levels and also for tetrafluoroborate-doped polypyrrole. A second-order polynomial is found to fit the observed data better than either of the existing models. The polynomial is of the form σ(P) = − aP² + bP+ σ(0).     

The role of anthraquinone sulfonate dopants in promoting performance of polypyrrole composites as pseudo-capacitive electrode materials

We report the role of anthraquinone sulfonate dopants in promoting performance of electro-synthesized polypyrrole (PPy) composites for use in electrochemical supercapacitors. The incorporation of anthraquinone sulfonate species into the polymer matrix can significantly improve the surface area of PPy composites that are composed of submicron-/nano-sized particles, as evidenced from scanning electron microscopy (SEM) results. Cyclic voltammetry and galvanostatic charge–discharge measurements in 1 M KCl solution reveal that these dopants result in an improved specific capacitance, a wide working potential range and enhanced long-cycle stability as compared to ClO₄^? dopant. Among the samples investigated, the resulting PPy/AQS (9,10-anthraquinone-2-sulfonic acid sodium salt) composite exhibits the highest specific capacitance of 608 F g^?1 at a scan rate of 5 mV s^?1 within a potential range between ?0.9 and 0.5 V (vs. saturated calomel electrode, SCE).     

Enhancement of the electrical conductivity of polypyrrole films on applying higher voltage

The effect of voltage on the conductivity of polypyrrole films has been investigated. It is found that the conductivity of the films increases with some structural change after the applied voltage reaches a higher value. The degree and the stability of the conductivity enhancement are related to the nature of the counter-anions doped in the polypyrrole films. A 65% increase in conductivity of the film doped with TsO⁻ is observed on applying higher voltage, and it remains stable after the treatment. The conductivity of the film doped with NO₃⁻ increases 47% on applying higher voltage, but it drops back to its original value quickly after the higher voltage is turned off. The structural change of PPy(TsO⁻) is studied through Vis and NIR absorption spectra.     

Negative differential resistance and sample conductivity in polypyrrole films

An unusual negative differential resistance (NDR) has been observed in I–V response in p-toluensulfonate-doped polypyrrole films, leading to a conductivity switching effect of almost four orders of magnitude. The effect appears at temperatures below 20 K for highly conducting samples while it is displaced to temperatures close to the room temperature for more resistive samples. The observed correlation between conductivity and switching phenomenon provides a fingerprint of the influence played by the sample nanostructure. The relation between the chemical structure of the material and the observed physical phenomenon is discussed.     

Microstructure and optical absorption properties of Au-dispersed CoO thin films

Au nanoparticles dispersed cobalt monoxide (CoO) composite films were fabricated via a chemical solution approach combined with a spin-coating processing. Au particles were spherical approximately and uniformly dispersed in the amorphous CoO matrix. The mean diameters of Au particles in the Au/CoO thin films with 40 mol% Au are about 30 nm. The optical absorption peaks due to the surface plasmon resonance (SPR) of Au particles were observed in the UV-vis absorption spectra in the wavelength range of 550-650 nm. The SPR peaks exhibit a red shift and intensify with increasing Au content from 10 to 40 mol%, but show a blue shift and weaken from 40 to 60 mol%. The band gap E_g decreases with increasing Au contents from 10 to 40 mol% but increases by further increasing Au content.     

Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films

Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electrochemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity σ of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole-coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity (σ_293 K = 4.5 × 10⁵ S m^?1) whereas the perchlorate doped one produced the lowest of all the films prepared (σ_293 K = 2 × 10⁴ S m^?1).     

The effect of polypyrrole coatings on the adhesion and structure properties of UHMWPE fiber

To improve the adhesion between ultrahigh molecular weight polyethylene (UHMWPE) fiber and polymer matrix, pyrrole is oxidatively polymerized on the UHMWPE fiber surface continuously. The micro-composite of polypyrrole (PPy)-coated fiber/epoxy was prepared and the fiber was studied by interfacial shear strength (IFSS) through a single fiber pull-out method. Compared with the UHMWPE fiber as-received, the mean value of IFSS between PPy-coated UHMWPE and epoxy increased from 1.06 MPa to 5.72 MPa. In addition, the surface morphology and structure of PPy-coated UHMWPE fiber were studied by SEM, FT-IR, DSC and DMA. The results showed that PPy-coated UHMWPE fiber surface was observed with some particles attached. Although there is no chemical interaction between PPy and UHMWPE chains, PPy has some interaction with UHMWPE molecular chains according to the results of DMA. The PPy coatings have an effect on the adhesion may be associated with the roughened surface of the fiber and upon intermolecular interaction.     

Photoinduced absorption and nonlinear optical properties of disubstituted polyacetylenes: Theory

In this paper, we summarize results of our recent large-scale correlated calculations of nonlinear optical spectra and photoinduced absorption (PA) spectra of phenyl-disubstituted polyacetylenes (PDPA). Calculations were performed on oligomers of PDPA's using correlated-electron Pariser–Parr–Pople (P–P–P) model and configuration interaction (CI) methodology. Computed PA spectra are compared with the recent experiments of Korovyanko et al., and good agreement is obtained between the two.     

Electrical conductivity and thermoelectric power of polypyrrole with different doping levels

The electrical conductivity and absolute thermoelectric power of the conducting polymer polypyrrole have been measured between approximately 4 K and 350 K. Normally-doped films had a conductivity of 26 Ω⁻¹ cm⁻¹, whilst lightly-doped films had a conductivity of 8 Ω⁻¹ cm⁻¹. The Mott variable-range hopping model for electrical conductivity is obeyed at higher temperatures for both types. The thermoelectric power is approximately linear in temperature, reaching about 5 μV K⁻¹ at 200 K, but is sublinear at higher temperatures and becomes constant above about 300 K. The Kuivalainen model, which explains the reported anomaly between optical and d.c. electrical conductivity, gives a good fit to the experimental data.     

Electronic properties of mislinked polypyrrole and polythiophene

Electronic properties of polypyrrole and polythiophene involving α-β linkages have been studied using the one-dimensional tight-binding SCF-CO (self consistent field-crystal orbital) method. It has been found that in such polymers the degree of π-conjugation is reduced and that the nature of the band gap varies compared with polymers consisting of only α-α′ (normal) linkages. It is mentioned that formation of the bipolaron structure along several pyrrole or thiophene rings with α-β linkages will be difficult.     

Optical absorption and vibrational spectroscopy of conducting polypyrrole under pressure

Polypyrrole in its conducting form was chemically synthesized using p-toluenesulfonic acid as doping agent. UV–Vis absorption and vibrational spectroscopy was used for characterization of the electronic properties. The measurements were conducted under high pressure up to 4 GPa which allows for observation of changes of the structural parameters without changing the chemical nature. The results are interpreted in terms of the stability of charge carriers. A change of the character of the charge carriers from bipolarons to polarons is suggested.     

A novel route to synthesis of photoluminescent dye/polypyrrole nanoparticles: Effects of intermolecular energy transfer on nucleation and growth of polypyrrole

Photoluminescent dye/polypyrrole nanoparticles were prepared by one-step polymerization of pyrrole monomer in the presence of the dye molecules under UV light illumination. Oxygen in the air was selected as an oxidant in this method. Optical properties of the nanoparticles were investigated, revealing that the nanoparticles exhibited higher photostability than pure RhB. In addition, it was found that the presence of both dye molecules and UV light played the important role in the formation of the nanoparticles. And then the mechanism for the formation of well-confined nanoparticles was explained via the effects of intermolecular energy transfer between the dye molecules and pyrrole monomer on nucleation and growth of polypyrrole.     

The influence of polymerization time and dopant concentration on the absorption of microwave radiation in conducting polypyrrole coated textiles

Temperature changes in conducting polypyrrole/para-toluene-2-sulphonic acid (PPy/pTSA) coated nylon textiles due to microwave absorption in the 8–9 GHz and 15–16 GHz frequency ranges were obtained by a thermography station during simultaneous irradiation of the samples. The temperature values are compared and related to the amounts of reflection, transmission and absorption obtained with a non-contact free space transmission technique, indicating a relationship between microwave absorption and temperature increase. Non-conductive samples showed no temperature increase upon irradiation irrespective of frequency range. The maximum temperature difference of around 4 °C in the conducting fabrics relative to ambient temperature was observed in samples having 48% absorption and 26.5 ± 4% reflection. Samples polymerized for 60 or 120 min with a dopant concentration of 0.018 mol/l or polymerized for 180 min with a dopant concentration of 0.009 mol/l yielded optimum absorption levels. As the surface resistivity decreased and the reflection levels increased, the temperature increase upon irradiation reduced.