Synthetic Metals (v.160, #11-12)
Thermal cis–trans conversion in thiophene oligomers
by Y. Kimura; Y. Katano; S. Tanaka; T. Yoshinari; H. Itoh; Y. Kuriyama; S. Nagasaka (pp. 1131-1135).
Thermal cis–trans conversion has been examined in oligothiophene single molecules encapsulated in the molecular vessels of cyclodextrin and Na-mordenite. At high temperatures, optical absorption intensities are enhanced in bithiophene, terthiophene and quinquethiophene, while the intensity of quarterthiophene is temperature independent. Optical absorption comes from uncompensated transition dipole moment due to the thermal torsion between cis and trans forms.
Keywords: PACS; 78.40.−q; 31.15.CtThiophene oligomers; Cis–trans; conversion; Torsion potential energy; Optical absorption spectra
Preparation of one-dimensional (1D) polyaniline–polypyrrole coaxial nanofibers and their application in gas sensor
by Shaohuang Weng; Jianzhang Zhou; Zhonghua Lin (pp. 1136-1142).
A facile and low-cost method has been developed to prepare one-dimensional (1D) polyaniline–polypyrrole (PANI–PPy) coaxial nanofibers (PPCF). The morphology and molecular structure of PPCF were proved by scanning electron microscopy, transmission electron microscopy, EDX, UV–vis, FTIR and Raman spectroscopy. A possible synthetic scheme for the synthesis of PPCF has been proposed. The electrical responses of PPCF to triethylamine (TEA) vapor were measured at room temperature. It was found that PPCF showed a rapid, sensitive and reversible conductance change upon exposure to TEA vapor at concentrations ranging from 1 to 1000ppm. The results suggested that the comprehensive performance of the gas sensor using PPCF was better than the results obtained using PANI nanofibers and PPy separately. In addition, a sensing mechanism was proposed.
Keywords: Polyaniline–polypyrrole; Coaxial nanofibers; Gas sensor; TEA
Melt blending of carbon nanotubes/polyaniline/polypropylene compounds and their melt spinning to conductive fibres
by A. Soroudi; M. Skrifvars (pp. 1143-1147).
Blends of polypropylene with polyaniline and multi-walled carbon nanotubes have been prepared and melt spun to fibre filaments. The resulted filaments have been characterised regarding conductivity, morphology, thermal and mechanical properties. DSC suggests that carbon nanotubes act as nucleating sites for PP/polyaniline blend. Electrical conductivity has been measured for blends with extruded rod shape, as-spun fibre filaments and fibres made under draw ratio of four. Polypropylene containing 20wt% polyaniline polymer modified with 7.5wt% carbon nanotubes shows the maximum conductivity among all the samples, about 0.16S/cm.
Keywords: Conducting fibre; Melt spinning; Polyaniline; Carbon nanotube
3,12-Dimethoxy-7,8-dicyano-helicene as a novel emissive material for organic light-emitting diode
by Somboon Sahasithiwat; Tipwan Mophuang; Laongdao Menbangpung; Siriporn Kamtonwong; Thanasat Sooksimuang (pp. 1148-1152).
3,12-Dimethoxy-7,8-dicyano-helicene (DDH) was introduced as a novel emissive material for organic light-emitting diode. It shown good thermal stability and no glass transition temperature was observed. The LUMO, HOMO and energy band gap (−3.3, −5.9 and 2.6eV) of this compound were determined using cyclic voltammetry technique. Fluorescence quantum yield of DDH in chloroform is 0.27. The turn-on voltage of OLEDs with a configuration of ITO/PEDOT:PSS/DDH/Ca/Al was not a function of DDH thickness in a range of 60–100nm. The best OLED, in which DDH thickness was 100nm, exhibited a turn-on voltage of 3.7V with maximum brightness of 1587cd/m2 at 8.0V and 281mA/cm2. The maximum current efficiency and power efficiency were 0.64cd/A and 0.29lm/W, respectively. The CIE coordinates of the OLED electroluminescence, however, appeared to depend on the applied voltage as they were (0.38,0.47) at 5.0V and (0.51,0.44) at 8.0V.
Keywords: Helicene; Organic light-emitting diode; Electroluminescence
Synthesis and thermoelectric properties of hydrochloric acid-doped polyaniline
by Junjie Li; Xinfeng Tang; Han Li; Yonggao Yan; Qingjie Zhang (pp. 1153-1158).
A series of hydrochloric acid-doped polyaniline (PANI) were prepared by chemical oxidative polymerization. And the effects of HCl-doping concentration on the thermoelectric properties in the temperature range of 303–423K were discussed. The results show that an increase in HCl-doping concentration will lead to a trend of first increase and then decrease in both the electrical conductivity and thermoelectric figure-of-merit ZT, accompanied by the opposite trend of the Seebeck coefficient. The maximum ZT can reach 2.67×10−4 at 423K when HCl-doping concentration is 1.0M. Moreover, the temperature dependence of the electrical conductivity shows a transition from non-metallic to metallic sign with doping level increasing, while the Seebeck coefficient of all the samples has a metallic character.
Keywords: Polyaniline; Hydrochloric acid-doping; Metallic character; Thermoelectric properties
Conducting polypyrrole with nanoscale hierarchical structure
by Yongqin Han; Xutang Qing; Sunjie Ye; Yun Lu (pp. 1159-1166).
Conducting polypyrrole (PPy) with nanoscale hierarchical structure is chemically synthesized in an aqueous solution in the presence of cetyltrimethylammonium bromide (CTAB) and 1,5-naphthalene disulfonic acid (1,5-NDA). The effect of synthetic conditions including concentration of CTAB and pyrrole, reaction temperature, oxidants and their introduced modes on the PPy hierarchical nanostructure is systematically investigated. A hypothesis for the hierarchical structure formation of PPy with the aid of CTAB/1,5-NDA/pyrrole supramolecular template is presented, in which the pyrrole is polymerized in imitation of the CTAB/1,5-NDA/pyrrole crystal shape. The electrochemical performances of representative PPy sample show that the PPy with hierarchical nanostructures has potential application as supercapacitor materials.
Keywords: Polypyrrole; Nanoscale hierarchical structure; Supramolecular templates
Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC
by Qi Qin; Jie Tao; Yan Yang (pp. 1167-1172).
Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5M H2SO4 solution containing 0.3M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials ( Eappl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I3−/I− reaction was electrodeposited at 1.0V Eappl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the Eappl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.
Keywords: Polyaniline; Electrochemical; Stainless steel; Potentiostatic; Dye-sensitized solar cell
Phosphine functionalized polyaniline nanostructures
by Cosmin Laslau; William Henderson; Zoran D. Zujovic; Jadranka Travas-Sejdic (pp. 1173-1178).
We study the problem of limited functionalization options for polyaniline through the surface attachment of phosphine coupling reagents. These studied linkers are P(CH2OH)3 and Ph2PCH2OH, and are attached to both conventional and nanostructured polyaniline. Additionally, model compounds are considered, extending the scope of our analysis. The successful attachment results indicate the potential for further functionalization, using the hydroxymethyl terminal groups of the phosphines for primary and secondary amine chemistry. These results should enable the development of sensitive and molecule-specific polyaniline-based devices.
Keywords: Polyaniline; Nanostructures; Nanotubes; Phosphines; Functionalization
Synthesis of polyaniline nanostructures via soft template of sucrose octaacetate
by Hua Qiu; Shuhua Qi; Donghong Wang; Jin Wang; Xinming Wu (pp. 1179-1183).
Highly crystallized polyaniline (PANI) nanostructures were polymerized by oxidative polymerization in the presence of sucrose octaacetate acting as an in situ seed and a soft template, and ammonium peroxydisulfate (APS) acting as an oxidizing agent. PANI nanofibers and nanorods were obtained using 2 and 3g sucrose octaacetate, respectively. The nanostructures containing irregular-shaped agglomerates, such as particulate particles and scaffolds were observed with increasing the concentrations of sucrose octaacetate. The polymerized PANI was characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetry analysis (TGA). Results showed that the presence of sucrose octaacetate during polymerization could only induce a change in morphology, but could not influence the molecular structure of the resulting PANI. Compared with those derived with 1, 3, and 4g sucrose octaacetate, the polymerized PANI from 2g sucrose octaacetate possessed higher thermal stability and electrical conductivity due to its higher crystallinity and highly ordered structure. A mechanism for the formation of PANI nanostructures is also proposed.
Keywords: Polyaniline; Sucrose octaacetate; Nanofibers; Nanorods; In situ; seed; Soft template
Thermally stable fluorescent blue organic light-emitting diodes using spirobifluorene based anthracene host materials with different substitution position
by Sang Eok Jang; Chul Woong Joo; Kyoung Soo Yook; Joon-Woo Kim; Chil-Won Lee; Jun Yeob Lee (pp. 1184-1188).
Thermally stable blue organic light-emitting diodes (OLEDs) were developed using anthracene based host materials with a spirobifluorene group. 4-Bromospirobifluorene and 2-bromospirobifluorene were attached to the anthracene core and the effect of the substitution position on the physical properties and device performances of the blue fluorescent OLEDs was investigated. The 4-spirobifluorene substitution was better than the 2-spirobifluorene substitution in terms of thermal stability and widened the bandgap of the anthracene based host material due to the geometrical structure of the material. However, the wide bandgap of the host material with 4-spirobifluorene had negative effect on the current density and efficiency of the blue devices.
Keywords: Blue organic light-emitting diode; Spirobifluorene; Anthracene; High efficiency; Thermal stability; Bandgap
Polymerization of pyrrole derivatives on polyacrylonitrile matrix, FTIR–ATR and dielectric spectroscopic characterization of composite thin films
by Suat Cetiner; Hale Karakas; Romeo Ciobanu; Marius Olariu; N. Ugur Kaya; Cem Unsal; Fatma Kalaoglu; A. Sezai Sarac (pp. 1189-1196).
Oxidative polymerization of acrylonitrile (AN) initiated by Ce(IV)–oxalic acid redox system in the aqueous medium was performed and polyacrylonitrile (PAN)/polypyrrole (PPy) composite thin films were prepared by polymerization of pyrrole on polyacrylonitrile matrix. Effect of concentration of pyrrole derivatives on the resulting polymeric film properties was investigated. The influence of the pyrrole derivative type and content on the dielectric permittivity, dielectric loss and electrical properties of the composite films were analyzed in the frequency range from 0.05Hz to 10MHz. For a selected concentration of 200μl of composite films at 107Hz, the conductivity was found to be in the following order: PAN–PPy
Keywords: Dielectric properties; Conducting composite film; Polypyrrole
Low band gap conjugated polymers consisting of alternating dodecyl thieno[3,4- b]thiophene-2-carboxylate and one or two thiophene rings: Synthesis and photovoltaic property
by Baek Myung-Jin; Soo-Hyoung Lee; Kyukwan Zong; Youn-Sik Lee (pp. 1197-1203).
In order to develop conjugated polymers with low band gaps and deep HOMO levels, copolymers consisting of alternating dodecyl thieno[3,4- b]thiophene-2-carboxylate and one (DTT-T1) or two thiophene rings (DTT-T2) were synthesized. The estimated optical band gap and HOMO level of DTT-T1 and DTT-T2 were ∼1.58/1.61 and ∼−5.15/−5.20eV, respectively, indicating that the polymers have relatively low band gaps and deep HOMO levels, as compared to many other reported polymers. Photovoltaic devices were fabricated using DTT-T2 and a fullerene derivative (PCBM), and whose power conversion efficiency was 0.21% under the illumination of AM 1.5 (100mW/cm2). The low conversion efficiency of the devices was attributed to the inefficiency of exciton formation due to the low absorption coefficient and self-quenching of the polymer as well as the un-optimized device conditions.
Keywords: Conjugated polymer; Thieno[3,4-; b; ]thiophene; Low band gap; Photovoltaic device
Self-assembled necklace-like polyaniline nanochains from elliptical nanoparticles
by Yingmei Li; Chuanqin Zhang; Guicun Li; Hongrui Peng; Kezheng Chen (pp. 1204-1209).
Necklace-like polyaniline nanochains assembled by elliptical nanoparticles have been synthesized in chitosan aqueous solution by a facile dispersion polymerization method. The synthetic procedure is very simple and easy to scale up. A new self-assembly process of elliptical nanoparticles has been proposed for the formation of necklace-like polyaniline nanochains with fluctuant diameters.High quality necklace-like polyaniline nanochains assembled by elliptical nanoparticles have been synthesized in chitosan aqueous solution by a facile dispersion polymerization method. The synthetic procedure is very simple and easy to scale up. The necklace-like nanochains coated by a layer of chitosan are typical doped polyaniline in its emeraldine salt form, which is easy to form stable polyaniline dispersion in water. Open-circuit potential measurements show that the rate of polymerization of aniline has a substantial decrease due to the steric effects of chitosan. The synthetic parameters, such as reaction times, and the concentrations of chitosan, aniline, and dopant acid, have profound influences on the sizes and morphologies of polyaniline nanostructures. A new self-assembly process of elliptical nanoparticles has been proposed for the formation of necklace-like polyaniline nanochains with fluctuant diameters, which is different from that of other one-dimensional polyaniline nanostructures including nanofibers and nanotubes.
Keywords: Chitosan; Conducting polymers; Dispersion polymerization; Polyaniline; Self-assembly
Multicolor emitting from a single component emitter: New iridium(III) complexes with ancillary ligand 2-(2-hydroxyphenyl) benzothiazole
by Yuying Hao; Xiaoxia Guo; Liping Lei; Jianning Yu; Huixia Xu; Bingshe Xu (pp. 1210-1215).
Four new types of Ir(III) complexes (ppy)2Ir(LX) (ppy=2-phenylpyridine, LX=BTZ, 3-MeBTZ, 4-MeBTZ, and 4-TfmBTZ) were synthesized and investigated by optical spectroscopy, electrochemistry as well as density functional theory (DFT). These complexes all exhibit multi-emission bands under ultraviolet light excitation at room temperature because there are efficient energy transfers between different excited states (1LC,1MLCT,1ILCT,3MLCT,3ILCT), especially for complexes I–III. The blue emitting relates to the fluorescence of Ir(R-BTZ) and the green emission originates in3MLCT emission of Ir(ppy)2 fragment. The red emission corresponds to3ILCT transition (R-BTZ→ppy) for complexes I–III, but3MLCT transition of Ir(4-TfmBTZ)2 fragment for (ppy)2Ir(4-TfmBTZ). The red emission peak wavelength can be fine-tuned from 583 to 626nm by the electron withdrawing or donating substituent at 3- or 4-position of BTZ ligand. For these single component complexes with multicolor emitting, a very promising application is the generation of white light. Although these complexes span non-uniformly the spectral range of the visible region and consequently are insufficient to produce satisfactory white light characteristics, the luminescence mechanism of them provides a new strategy for designing organic white light-emitting material.
Keywords: Iridium(III) complexes; Multicolor emitting; Single component
Bistability and improved hole injection in organic bistable light-emitting diodes using a quantum dot embedded hole transport layer
by Soon Ok Jeon; Kyoung Soo Yook; Jun Yeob Lee (pp. 1216-1218).
Organic bistable light-emitting diodes (OBLED) were developed by using a quantum dot embedded hole transport layer in the organic light-emitting diodes. The driving voltage of the OBLED was decreased due to the good hole transport properties of quantum dot embedded hole transport layer and the OBLED also showed bistability at negative bias due to the switching behavior of the quantum dot based hole transport layer. The origin for the switching behavior of the OBLED was confirmed by fabricating organic bistable device with the quantum dot embedded hole transport layer.
Keywords: PACS; 85.60.jbOrganic bistable light-emitting diode; Quantum dot; Bistability
Fabrication and characterization of cuprous oxide: fullerene solar cells
by Ryosuke Motoyoshi; Takeo Oku; Atsushi Suzuki; Kenji Kikuchi; Shiomi Kikuchi; Balachandran Jeyadevan; Jhon Cuya (pp. 1219-1222).
Cuprous oxide (Cu2O)-based solar cells with fullerene (C60) were fabricated on indium tin oxide (ITO) by a spin-coating method. The microstructure and cell performance of the solar cells with the Cu2O:C60 structure was investigated. A photovoltaic device based on an ITO/Cu2O:C60 bulk heterojunction structure fabricated by the spin-coating method provided short-circuit current density of 0.11mAcm−2 and open-circuit voltage of 0.17V under an Air Mass 1.5 illumination. The microstructures of the Cu2O active layer were examined by using X-ray diffraction and transmission electron microscopy. The energy levels of the present solar cells are also discussed.
Keywords: Bulk heterojunction solar cells; Cuprous oxide; Fullerene; Spin-coating method
Ionic liquid-stabilized nanoparticles of charge transfer-based conductors
by Dominique de Caro; Kane Jacob; Christophe Faulmann; Jean-Pierre Legros; François Senocq; Jordi Fraxedas; Lydie Valade (pp. 1223-1227).
Well-dispersed nanoparticles of molecule-based conductors, namely TTF·TCNQ and TTF[Ni(dmit)2]2, have been prepared in organic solution using 1-butyl-3-metylimidazolium tetrafluoroborate as a stabilizing agent. TTF·TCNQ nanoparticles (prepared at room temperature) exhibit sizes ranging from 2 to 5.5nm, whereas those of TTF[Ni(dmit)2]2 (prepared at −80°C) are larger (sizes in the 16–45nm range). Nanoparticle powders have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and by transport measurements.
Keywords: Nanoparticles; Molecular conductors; Ionic liquids; Tetrathiafulvalene; Dithiolene complexes
Investigation of polyaniline co-doped with Zn2+ and H+ as the electrode material for electrochemical supercapacitors
by Jie Li; Mu Cui; Yanqing Lai; Zhian Zhang; Hai Lu; Jing Fang; Yexiang Liu (pp. 1228-1233).
Polyaniline co-doped with Zn2+ and H+ was synthesized in aqueous HCl solution containing ZnCl2, and tested for its supercapacitive behavior in three-electrode or two-electrode system with 1.0M H2SO4 as electrolyte by cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) techniques were employed for characterization of polyaniline co-doped with Zn2+ and H+. Compared with polyaniline doped with H+, it shows a larger specific capacitance of 369Fg−1. Moreover, the specific capacitance remains 90% after 1000 cycles at a current density of 0.5Ag−1, indicating good cycleability.
Keywords: Supercapacitor; Polyaniline; Zn; 2+; ions; Co-doped
Ex situ XANES, XPS and Raman studies of poly(3,4-ethylenedioxythiophene) modified by iron hexacyanoferrate
by A. Lisowska-Oleksiak; A.P. Nowak; M. Wilamowska; M. Sikora; W. Szczerba; Cz. Kapusta (pp. 1234-1240).
X-ray (XPS and XANES) and Raman spectra of poly(3,4-ethylenedioxythiophene) (pEDOT) modified by iron hexacyanoferrate (Fehcf) network are presented. XANES studies allowed to postulate an octahedral surrounding of iron atoms in the material and identified nitrogen and carbon atoms as nearest neighbourhoods. XPS measurements reveal iron–nitrogen and iron–carbon bonds, supporting the XANES results. Chemical interaction between sulphur from pEDOT and iron was also evidenced by XPS. Although both methods give proof of Prussian Blue structure inside the polymer, Raman studies did not show any signal typical for CN at about 2160cm−1 ( ν). However, the presence of Fehcf was confirmed by the stretching vibrations of Fe–N bond at 146cm−1 and Fe–CN vibrations at 270cm−1. AFM imaging was performed to illustrate the roughness and morphology of the pEDOT/Fehcf surface.
Keywords: Poly(3,4-ethylenedioxythiophene); Prussian Blue; XANES; XPS; Raman spectroscopy; Metal hexacyanoferrate
Theoretical study the trap and carrier-density dependent electron mobility in pentacene ab-plane by the steady master equation
by Shiwei Yin; Yongmei Yang; Yanfeng Lv (pp. 1241-1246).
The steady state master equation coupled Marcus–Hush electron transfer theory is developed to calculate the two-dimensional electron and hole mobilities in pentacene ab-plane. In this paper, we numerically investigated the influences of the random distributed traps and charge-carrier densities on the 2D mobilities. The study showed that shallow traps (<7.5 kT) give few effects on the mobilities for various carrier densities, while deep traps (>10 kT) remarkably decrease mobilities, in particularly, when the carriers density cannot quenched them. However, when the traps are fully quenched due to large carrier densities, the mobility will be nearly back to their intrinsic mobility values.
Keywords: Pentacene; Trap-dependant electron mobility, Master equation
Synthesis of ternary intercalation compounds of carbon fiber
by Asami Takenaka; Tomoki Tsumura; Masahiro Toyoda (pp. 1247-1251).
Ternary intercalation compounds of carbon fiber (ICCF) were successfully synthesized by soaking pitch-based carbon fibers in solvents such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF) containing dissolved alkali metals (lithium, sodium, or potassium). ICCF with stage-1 and random stage was synthesized in alkali metal–DME and potassium–THF systems using different types of carbon fibers. However, ICCF with stage-1 could not be synthesized in lithium– or sodium–THF systems using carbon fibers with a low graphitization degree. Furthermore, the influence of the graphitization degree in the synthesis of ICCF was discussed. The graphitization degree of the host carbon fiber, in addition to the dimensions and steric structure of the intercalated complex affected the formation of TICCF.
Keywords: Ternary intercalation compounds; Carbon fibers; Graphitization degree; Alkali metal
Electrochemical study on the semiconductor properties and fractal dimension of poly ortho aminophenol modified graphite electrode in contact with different aqueous electrolytes
by M.G. Mahjani; A. Ehsani; M. Jafarian (pp. 1252-1258).
The fractal dimension of poly ortho aminophenol (POAP) films in the presence of different counter ions was investigated. The POAP films were deposited on graphite electrode by cyclic voltammetry. The deposited films were also characterized by electrochemical impedance spectroscopy (EIS) in wide frequency range. The length scale, the distances between two nearest points that the anions somehow sense (by yardstick of the size of their jump-length), were also derived. The resulting Mott-Schottky plot of the polymer capacitance describes the reduced polymer as a p-type semiconductor with a flat band potential of about 200mV vs. SCE. The discussion shows that the nature of the anion plays a major role on the electrochemical behavior of the polymer.
Keywords: Impedance; Poly ortho aminophenol; Semiconductor; Fractal
A highly efficient deep blue fluorescent OLED based on diphenylaminofluorenylstyrene-containing emitting materials
by Seul Ong Kim; Kum Hee Lee; Gu Young Kim; Ji Hoon Seo; Young Kwan Kim; Seung Soo Yoon (pp. 1259-1265).
We have designed and synthesized five blue emitters based on diphenylaminofluorenylstyrene emitting core groups. Multilayered OLEDs were fabricated using these materials as dopants in a 2-methyl-9,10-di(naphthen-2-yl)anthracene (MADN) host. One of them in particular a deep blue OLED using dopant 9-[4-(2-diphenylamino-9,9-diethylfluoren-7-yl)phenyl]-9-phenylfluorene (3) at 15% doping concentration exhibited a maximum luminance of 4720cdm−2 at 9.0V, a luminous efficiency of 5.3cdA−1 at 20mAcm−2, a power efficiency of 2.9lmW−1 at 20mAcm−2, an external quantum efficiency of 4.8% at 20mAcm−2, and CIE coordinates ( x=0.15, y=0.13) at 8.0V. Furthermore, this deep blue device had very stable CIE coordinates of ( x=0.15, y=0.13) that did not vary with doping concentration from 5% to 15%.
Keywords: OLEDs; Blue fluorescent dopant; Diphenylaminofluorenylstyrene; Horner–Wadsworth–Emmons reaction
Synthesis and characterization of the carbon nanotube-based composite materials with poly(3,4-ethylenedioxythiophene)
by Tran Thanh Tung; Ji Hye Yeon; Tae Young Kim; Kwang S. Suh (pp. 1266-1272).
We report a procedure to prepare a conducting nano-composites composed of multi-walled carbon nanotubes (MWNTs) and PEDOT by using a poly(sodium 4-styrenesulfonate) (PSSNa) as a inter-linking molecule between MWNT and PEDOT. When PSSNa chains are introduced on the MWNTs via physicochemical interaction, the surface of MWNT becomes negatively charged, and PSS-modified MWNTs promote the effective association of the positively charged PEDOT chains. The resulting MWNT-PSS/PEDOT composites are characterized by a better interconnection between MWNT and PEDOT components.
Keywords: Carbon nanotubes; Composites; Self-assembly; Poly(3,4-ethylenedioxythiophene)
Newly synthesized fused heterocyclic compounds in thin films with semiconductor properties
by L. Leontie; R. Danac; I. Druta; A. Carlescu; G.I. Rusu (pp. 1273-1279).
Temperature-dependent electrical conductivity and thermoelectric power of some recently synthesized fused heterocyclic compounds (nonsymmetrical bisindolizines), are studied. Thin-film samples ( d=0.10–0.20μm) deposited from dichloromethane solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 300–600K.The studied compounds show typical p-type semiconductor behavior. The activation energy of the electrical conduction ranges between 0.90 and 1.17eV, while the ratio of charge carrier mobilities was found in the range 0.94–0.97.Some correlations between semiconducting parameters and molecular structure of the organic compounds have been discussed.In the higher temperature range (373–601K), the electronic transport in examined compounds can be interpreted in terms of the band gap representation model, while in the lower temperature range, the Mott's variable-range hopping conduction model was found to be appropriate.
Keywords: Organic compounds; Thin films; Chemical synthesis; Electrical conductivity
Electro-stiffening in polypyrrole films: Dependence of Young's modulus on oxidation state, load and frequency
by Tina Shoa; Tissaphern Mirfakhrai; John D.W. Madden (pp. 1280-1286).
Electrochemically driven actuation of polypyrrole in aqueous sodium hexafluorophosphate (NaPF6) solution has been shown to produce repeated large strains (>6%) at low voltages and with high conductivity, making it one of the most promising electroactive conducting polymers. Little is known about the voltage dependent stiffness of this version of the polymer. This information is important in determining the strain as a function of load. In this paper the complex Young's modulus (storage and loss components) of a hexafluorophosphate-doped polypyrrole film in aqueous NaPF6 electrolyte at different oxidation states, under various loads and as a function of the frequency of the applied load, is investigated. Uniformity of doping was ensured by allowing enough time to reach steady state charge levels, and the creep during measurements was minimized by using preconditioning cycles. The results of this study show that storage modulus decreases (from 1GPa to 0.80GPa) as the polypyrrole oxidation potential increases (from −0.4V to +0.4V versus Ag/AgCl reference electrode). The loss modulus, on the other hand, increases from 55MPa to 80MPa. An increasing trend in the Young's modulus is also observed with the applied load. The storage modulus increases from 0.65GPa to 1GPa by increasing the applied load from 0.2MPa to 2.5MPa. The modulus is found to increase with time through the experiment, which may be due to stretch alignment of the polymer. It is also observed that complex Young's modulus increases in proportion to the logarithm of frequency.
Keywords: Polypyrrole actuator; Young's modulus
Fabrication of aligned microwire arrays of perylene bisimide by micromolding in capillary
by Yunoh Jung; Jangwon Seo; Jong H. Kim; Dong Ryeol Whang; Se Hoon Gihm; Chong Rae Park; Soo Young Park (pp. 1287-1290).
In this work, we synthesized a novel perylene tetracarboxylic acid diimides derivative (APBI-G) which shows a strong self-assembling tendency to the semiconducting nano/microwires based on the augmented intermolecular hydrogen bonding interaction. We demonstrate the spinning of continuous thread of APBI-G from the liquid–liquid interface and also the fabrication of patterned nano/microwire arrays using MIMIC (micromolding in capillaries) method. MIMIC-fabricated APBI-G nano/microwires showed the excellent uniaxial orientation, large birefringence, and reproducible electrical conductivity (1.93±0.47×10−6Scm−1).
Keywords: Organic nanowire; Soft lithography; Electrical conductivity; Organic devices; Naphthalene; Diimide
Poly( p-phenylenevinylene) derivatives with conjugated thiophene side chains: Synthesis, photophysics and photovoltaics
by Ping Shen; Tianpeng Ding; Hui Huang; Bin Zhao; Songting Tan (pp. 1291-1298).
Three novel poly( p-phenylenevinylene) (PPV) derivatives with conjugated thiophene side chains,P1,P2 andP3, were designed and synthesized for application in polymer solar cells (PSCs). The effects of the conjugated side chains on the thermal, photophysical, electrochemical and photovoltaic properties of these polymers were investigated. The polymers exhibited good thermal stability and film-forming ability. The absorption spectra indicated that the short conjugated side chains have slight influence on the UV-region spectra of PPVs; whereas with increasing the length of conjugated side chains, the absorption of the UV-region red-shifted. The photoluminescence spectra reveal that complete exciton energy transfer occur from the conjugated side chains to the main chains of the polymers. The polymers emitted yellow-orange light with the emission maximum peaks in the region of 525–550nm in chloroform solution and 611–616nm in thin films. Cyclic voltammograms displayed that the band gaps were reduced effectively by the attachment of the conjugated thiophene side chains. The bulk heterojunction solar cells were fabricated based on the blend of the polymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in a 1:4 weight ratio. The maximum power conversion efficiency (PCE=0.53%) was obtained by usingP3 as the electron donor under the illumination of AM 1.5, 100mW/cm2.
Keywords: Poly(; p; -phenylenevinylene); Conjugated side chains; Photophysics; Synthesis; Polymer solar cells; Thiophene
Chemical synthesis of cobalt oxide thin film electrode for supercapacitor application
by S.G. Kandalkar; D.S. Dhawale; Chang-Koo Kim; C.D. Lokhande (pp. 1299-1302).
Cobalt oxide thin film electrode was grown on copper substrate from an aqueous alkaline bath containing cobalt chloride as a cobalt source by adopting simple and inexpensive chemical deposition method and characterized for structural and morphological studies. The supercapacitive properties of cobalt oxide electrode were studied in aqueous KOH electrolyte solution. The effect of electrolyte concentration on specific capacitance and the stability of cobalt oxide electrode were studied. The highest specific capacitance achieved with cobalt oxide films was 118Fg−1. The specific energy ( E), specific power ( P) and coulomb efficiency ( η%) were 5.8Whkg−1, 0.33kWkg−1 and 93.44%, respectively.
Keywords: Cobalt oxides; Thin films; Chemical synthesis; Energy-storage
Structure and properties of selenious acid doped polyaniline with varied dopant content
by Ngo Trinh Tung; Hoik Lee; Yeari Song; Nguyen Duc Nghia; Daewon Sohn (pp. 1303-1306).
In this study, the effects of dopant content on the structure, especially crystalline structure, and properties of selenious acid doped polyaniline (PAni) were investigated. The structure and properties of PAni were characterized by X-ray diffraction, FTIR spectroscopy, UV–vis spectroscopy, DSC, and TGA. By varying the dopant/monomer molar ratio (D/M), the morphology as well as the crystalline structure of PAni was significantly changed. The presence of water in the crystalline structure of PAni prepared with a low D/M ratio caused a change in the d-spacing of the PAni crystalline structure. The oxidation level and doping degree of PAni were also changed by varying the D/M ratio. The electrical conductivity of PAni increased with increasing D/M ratio, and the thermal stability of PAni in the doped state was about 200°C for different D/M ratios.
Keywords: Polyaniline; Selenic acid; Selenious acid; Conductivity
Synthesis of potential capacitive Poly 4, 4′-diaminodiphenyl sulphone–metal nanocomposites and their characterizations
by C. Vedhi; J. Anandha Raj; N. Gopal; R.M. Somasudaram; P. Manisankar (pp. 1307-1312).
4, 4′-Diaminodiphenyl sulphone was polymerized (with lithium/cobalt/lithium–cobalt salts) by chemical oxidation method using potassium perdisulphate. The solubility of the chemically prepared polymer–metal nanocomposite was ascertained and it showed good solubility in DMF, chloroform, trichloroethylene and DMSO. The PDDS–Li/Co/Li–Co nanocomposites were characterized by UV–vis and FTIR spectral studies. Amine and imine vibrations observed at 1593 and 1503cm−1 were shifted to lower wave numbers when the polymer–metal composites were formed. A single absorption peak due to the N–H stretching vibration of the imino groups of polymer–metal nanocomposite is observed around 3459cm−1 and it suggests the participation of NH group during polymerization. The X-ray diffraction studies revealed the formation of nano sized (82nm) crystalline polymer. The conductivity of the PDDS–Li–Co nanocomposite was determined to be 6.26×10−2Scm−1. SEM analysis showed mixed granular nature of the polymer–metal nanocomposite. The capacitance (159.04μF) of chemically synthesized PDDS–Li–Co nanocomposite is suggested as a potential capacitive material.
Keywords: 4, 4′-Diaminodiphenyl sulphone; Lithium nitrate; Cobalt sulphate; Polymer–metal nanocomposite; Capacitance
Synthesis, characterization, and NLO properties of novel chromophores based on dipicolinate
by Haibo Xiao; Lei Wang; Xiaoming Tao; Minjuan Chen (pp. 1313-1317).
Three novel chromophores, trans-dimethyl 4-(4′-methoxystyryl)pyridine-2,6-dicarboxylate (5), trans-dimethyl 4-(4′-nitrostyryl)pyridine-2,6-dicarboxylate (6), trans-dimethyl 4-(2-(1H-benzo[d]imidazol-2-yl)vinyl)pyridine-2,6-dicarboxylate (7) were synthesized and characterized. Their absorption, photoluminescence as well as two-photon absorption properties were studied. These compounds have strong linear absorption bands around 322–340nm. From femtoscond nonlinear transmission measurements, compounds5 and7 have effective two-photon cross sections ( σ) at 800nm.
Keywords: Dipicolinate; Two-photon absorption; Chromophore; Donor; Acceptor; Nonlinear optics
Self-assembling into interconnected nanoribbons in thin films of hairy rod poly(9,9-di(2-ethylhexyl)fluorene): Effects of concentration, substrate and solvent
by Rakchart Traiphol; Nipaphat Charoenthai; Toemsak Srikhirin; Dvora Perahia (pp. 1318-1324).
This study utilizes atomic force microscopy to investigate the self-assembling behaviors from dilute solution into thin film of a well-known conjugated polymer, poly(9,9-di(2-ethylhexyl)fluorene) (PF2/6). We have found that the structures of nanoscale aggregates depend on various experimental parameters including concentration, substrate and solvent. The self-assembling of PF2/6 from 0.05mg/mL solution in toluene onto SiO x/Si substrate results in the formation of interconnected nanoribbons with thickness and width of about 20 and 150nm, respectively. Varying polymer concentration and type of substrate (SiO x/Si or mica) significantly affects the nanoscale structures. The change of solvent to chlorobenzene, a slightly more polar solvent with slower evaporation rate, causes the growth of ribbon width to micron size with slight increase of the thickness. When the solvents with higher evaporation rate (i.e. chloroform and dichloromethane) are used, densely packed nanoribbons are obtained. Its width also grows to micron size. The measurements of UV/vis absorption and photoluminescence spectra detect some discrepancies in pattern, reflecting the variation of local chain organization within thin films prepared by using different solvents.
Keywords: Conjugated polymer; Self-organization; Aggregates; Photophysics; Nanostructures
Self-assembled polyaniline nanotubes and nanoribbons/titanium dioxide nanocomposites
by Marija Radoičić; Zoran Šaponjić; Jovan Nedeljković; Gordana Ćirić-Marjanović; Jaroslav Stejskal (pp. 1325-1334).
Self-assembled polyaniline (PANI) nanotubes, accompanied with nanoribbons, were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium, in the presence of colloidal titanium dioxide (TiO2) nanoparticles of 4.5nm size, without added acid. The morphology, structure, and physicochemical properties of the PANI/TiO2 nanocomposites, prepared at various initial aniline/TiO2 mole ratios, were studied by scanning (SEM) and transmission (TEM) electron microscopies, FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), conductivity measurements, and thermogravimetric analysis (TGA). The electrical conductivity of PANI/TiO2 nanocomposites increases in the range 3.8×10−4 to 1.1×10−3Scm−1 by increasing aniline/TiO2 mole ratio from 1 to 10. The morphology of PANI/TiO2 nanocomposites significantly depends on the initial aniline/TiO2 mole ratio. In the morphology of the nanocomposite synthesized using aniline/TiO2 mole ratio 10, nanotubes accompanied with nanosheets prevail. The nanocomposite synthesized at aniline/TiO2 mole ratio 5 consists of the network of nanotubes (an outer diameter 30–40nm, an inner diameter 4–7nm) and nanorods (diameter 50–90nm), accompanied with nanoribbons (a thickness, width, and length in the range of 50–70nm, 160–350nm, and ∼1–3μm, respectively). The PANI/TiO2 nanocomposite synthesized at aniline/TiO2 mole ratio 2 contains polyhedral submicrometre particles accompanied with nanotubes, while the nanocomposite prepared at aniline/TiO2 mole ratio 1 consists of agglomerated nanofibers, submicrometre and nanoparticles. The presence of emeraldine salt form of PANI, linear and branched PANI chains, and phenazine units in PANI/TiO2 nanocomposites was proved by FTIR and Raman spectroscopies. The improved thermal stability of PANI matrix in all PANI/TiO2 nanocomposites was observed.
Keywords: Nanocomposites; Nanoribbons; Nanostructures; Nanotubes; Polyaniline; Titanium dioxide
Electrochemical relaxation study of polythiophene as a conducting polymer (II)
by A.A. El-Maghraby; G.M. Abou-Elenien; G.M. El-Abdallah (pp. 1335-1342).
The electrosynthesis of polythiophene films from thiophene, 2,2′,5,2″-terthiophene, 3-methylthiophene and 3-bromothiophene monomers was investigated using different electrochemical techniques. The stability and electrical conductivity of the prepared films were studied. The most stable polythiophene film was obtained using galvanostatic technique in acetonitrile solvent and TBAPF6 as a supporting electrolyte at 5°C, except in the case of electropolymerization of 3-bromothiophene the most stable film was obtained potentiodynamically. The relaxation kinetics of the films was extensively studied. It was found that a very thin film would hardly shows the slow relaxation. Also by using TBAPF6 as an electrolyte, the most sensitive film was obtained, which has the lowest relaxation. The relaxation time is sharply affected by increasing the donor number of the solvent used and also by temperature.
Keywords: Electropolymerization; Relaxation studies; Polythiophene; Conducting polymer; Film building
Self-dispersed polyaniline derivative extending electrochemical activity to neutral media
by Xingwei Li; Shirong Pan; Tao Zhuang; Gengchao Wang (pp. 1343-1348).
Self-dispersed poly-N-[5-(8-quinolinol)ylmethyl]aniline, which can be easily dispersed in some organic solvents without any dispersant, has been prepared by oxidative polymerization of 5-(anilinomethyl)-8-hydroxyquinoline. Although its conductivity only reaches 1.45×10−3Scm−1, it possesses good redox reversibility in aqueous electrolyte ranging from pH 1.0 to 7.0, and its cyclic voltammetry curves also show good cycling stability in the aqueous medium of pH 5.0. It will be a promising material for several applications such as biosensors due to increasing the operating pH window in aqueous media.
Keywords: Polyaniline derivatives; Self-dispersed; Electrochemical activity
Suppression of the magneto resistance in high electric fields of polyacetylene nanofibers
by A. Choi; H.J. Lee; A.B. Kaiser; S.H. Jhang; S.H. Lee; J.S. Yoo; H.S. Kim; Y.W. Nam; S.J. Park; H.N. Yoo; A.N. Aleshin; M. Goh; K. Akagi; R.B. Kaner; J.S. Brooks; J. Svensson; S.A. Brazovskii; N.N. Kirova; Y.W. Park (pp. 1349-1353).
We present results of non-linear magneto resistance (MR) of polyacetylene nanofibers in high magnetic field up to H=30T at low temperature T=1.5K. The MR was proven to be of the spin origin; it reaches 16% at highest H. Unexpectedly, the MR was suppressed by increasing electric field E, vanishing at E≳5×104V/cm. It is understood that the doping induced spinless charged soliton pairs, which are initially confined to a certain distance because of the interchain phase correlations, and are deconfined in high electric fields, resulting in a vanishing magneto resistance (VMR). The role of the specific, degenerate ground state of the polyacetylene is confirmed by parallel studies of the different magneto resistances of polyaniline nanofibers which contrarily is not affected by the electric field.
Keywords: Polyacetylene nanofiber; Magneto resistance; Spinless charged soliton
Synthesis of discus-like Poly(3,4-ethylenedioxythiophene) nanoparticles using a bicellar template
by Kaixuan Sheng; Gaoquan Shi (pp. 1354-1358).
Poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles with discus-like morphology were synthesized by chemical oxidation polymerization using bicelles as a soft template. The bicelles were assembled from the surfactant molecules of sodium perfluorooctanoate (FC7) and cetyltrimethylammonium bromide (CTAB). The PEDOT nanodiscuses have an average diameter around 200nm and a central thickness of about 50nm. The effects of synthetic parameters, such as surfactant concentration, molar ratio of oxidant and monomer, reaction temperature on PEDOT nanostructures have been investigated.
Keywords: Conducting polymers; Bicelles; Nanoparticles; Templates
Electrochemically deposited polyethyleneimine films and their characterization
by Olivier Segut; Guillaume Herlem; Boris Lakard; Virginie Blondeau-Patissier; Michel Nardin; Simon Gree; Jean-Yves Rauch (pp. 1359-1364).
Polyethyleneimine films have been deposited on platinum electrode surfaces by electrochemical oxidation of ethylenediamine H2N–CH2–CH2–NH2 (EDA) in acetonitrile solutions. This electrochemical synthesis was realized by cyclic voltammetry and gravimetry techniques. Then, the characterization of the thin solid polyethyleneimine film was performed using X-ray photoelectron spectroscopy and infrared spectroscopy. It was also shown, using atomic force microscopy, that the solid polymeric coating has a granular and homogeneous structure. The influence of EDA concentration on the electropolymerization process was studied leading to the conclusion that the reaction is easier for high EDA concentration. Then, the influence of the nature and concentration of the supporting salt was investigated, showing that its nature is not very important, contrary to its concentration.
Keywords: Polyethyleneimine; Polymer coating; Spectroscopy; Microscopy; Electrochemical quartz crystal microbalance
Polypyrrole nanofibers synthesized via reactive template approach and their NH3 gas sensitivity
by Xiaoming Yang; Liang Li (pp. 1365-1367).
The synthesis of polypyrrole (PPy) nanofibers has been achieved via a simple reactive template approach. The reactive template of FeCl3 and methyl orange (MO) leads to the formation of uniform PPy nanofibers. Moreover, the fabrication of PPy nanofibers with high yield is realized, suggesting that this methodology is appropriate for the large-scale production of the corresponding nanomaterials. In contrast to the NH3 gas sensor based on bulk PPy, the gas sensor based on the as-prepared PPy nanofibers exhibits greatly improved performances.
Keywords: Polypyrrole; Nanofiber; Sensors
Highly efficient synthesis of thieno[3,4- b]thiophene derivatives and (opto)electrochemical properties of new low bandgap conjugated polymers
by Wha Sun Lee; Jin Hong Park; Myung-Jin Baek; Youn-Sik Lee; Soo-Hyoung Lee; Myoungho Pyo; Kyukwan Zong (pp. 1368-1371).
Various thieno[3,4- b]thiophene derivatives functionalized by n-octyl, 4- tert-butylphenyl, 4- n-butylphenyl, and 4- n-pentylphenyl were synthesized in a concise and efficient way. Previously reported synthetic processes were modified to produce target molecules in relatively high yields. Electrochemical and optical properties of polymers were examined by cyclic voltammetry and Vis–NIR spectrophotometry. The bandgap of electrochemically prepared polymers varied with substituents, ranging from 0.91eV to 0.98eV. While HOMO of conjugated polymers was raised by inductive effect of alkyl substituents, the bandgap was mainly determined by resonance stabilization of phenyl substituents.
Keywords: Thieno[3,4-; b; ]thiophene; Low bandgap; Conjugated polymer; NIR