Synthetic Metals (v.160, #7-8)
Fabrication and catalytic property of an Ag@poly(3,4-ethylenedioxythiophene) yolk/shell structure
by Youyi Xia; Liang Xu (pp. 545-548).
Poly(3,4-ethylenedioxythiophene) (PEDOT) hollow spheres with the size ranged from 210 to 850nm and a conductivity of 6×10−2Scm−1 have been prepared via electrochemical polymerization of 3,4-ethylenedioxythiophene in the presence of poly(vinyl pyrrolidone) as a soft template. Then, a novel Ag@PEDOT yolk/shell structure has been prepared simply and directly by a penetration and reduction approach. The morphology, formation, and the catalytic activity of the as-prepared Ag@PEDOT yolk/shell structure have been investigated. The experimental result shows that the as-prepared Ag@PEDOT yolk/shell structure exhibits excellent catalytic activity on reduction of p-nitrophenol. The employed approach may shed some light on preparing other noble metal@conductive polymer core/shell structure.
Keywords: Poly(3,4-ethylenedioxythiophene); Silver; Yolk/shell structure; Electrochemical polymerization
Synthesis and electro-optical properties of biphenyl analogues
by Ki-Soo Kim; Seonju Jeong; Cham Kim; Eunju Kim; Younghwan Kwon; Hoyoung Kim; Byoung-Dae Choi; Yoon Soo Han (pp. 549-555).
Three emitting materials containing a biphenyl core connected at both ends with phenoxazine or anthracene groups, 10-(3-(10 H-phenoxazin-10-yl)-6-phenylphenanthridin-8-yl)-10 H-phenoxazine (DPoPP), 8-(anthracen-10-yl)-3-(anthracen-9-yl)-6-phenylphenanthridine (DAnPP), and 2-(anthracen-10-yl)-7-(anthracen-9-yl)-4,5,9,10-tetrahydropyrene (DAnTP) were synthesized via the C–N Ullmann coupling or C–C Suzuki-coupling reaction. Optical properties, thermal stabilities and molecular orbital energies were analyzed as a function of their molecular microstructure. The thermal stabilities of them were influenced by biphenyl core. On the other hand, their emissions were primarily affected by anthracene or phenoxazine end groups. Two compounds with anthracene moiety at both ends showed electronic band structures suitable for host materials for reported blue dopants. The double-layer OLED (organic light-emitting diode) devices, ITO/NPD/synthesized material/LiF/Al, containing the synthesized materials as emitting layer emitted yellowish-green (DPoPP), greenish-blue (DAnPP) and blue (DAnTP).
Keywords: Phenoxazine; Anthracene; 6-Phenylphenanthridine; Tetrahydropyrene; Organic light-emitting diode
Crystal structure, band structure and electrical properties of κ-(BEDT-TTF)2SbF6 grown on a Si(001) electrode
by Aneta Aniela Kowalska; Jean-Philippe Savy; Dominique de Caro; Isabelle Malfant; Christophe Faulmann; Lydie Valade; Marie-Liesse Doublet; Jacek Ulanski (pp. 556-560).
The new κ-(BEDT-TTF)2SbF6 phase was grown by electrodeposition on a Si(001) electrode. This new phase was characterized by X-ray diffraction (XRD) and electronic conductivity measurements, accompanied by calculations of electronic band structures and Fermi surfaces. Below T=120K, a decrease in the electronic conductivity suggests a phase transition, attributed to anion ordering.
Keywords: Electrodeposition; BEDT-TTF; κ-Phase; Electronic band structures
Porous carbon nanotube electrodes supported by natural polymeric membranes for PEMFC
by Young Soo Yun; Hyeonseong Bak; Hyoung-Joon Jin (pp. 561-565).
A new type of porous multiwalled carbon nanotube (MWCNT) electrode with a macroporous networking inner-structure was prepared. First, the MWCNTs were homogeneously introduced inside and outside of a bacterial cellulose membrane with a 3D inter-connected network structure using ultrasound treatment and vacuum filtration in order to form the GDL. Second, the CL was formed on the surface of the GDL through vacuum filtration of the Pt incorporated MWCNTs (Pt/MWCNTs). Finally, the electrode was created through freeze-drying. The final electrode had a sheet resistance of 80Ω/□ and an electro-chemical active surface area (ECSA) of 10.1m2/g. Although the ECSA of the electrode did not have the efficiency (14.3m2/g) of a typical electrode (carbon cloth/Pt/carbon black), these results suggested that the new type of electrode has potential as a proton exchange membrane fuel cell.
Keywords: Multiwalled carbon nanotube; Proton exchange membrane fuel cells; Electrode; Porous carbon
Polyurethane/PEG-modified MWCNT composite film for the chemical vapor sensor application
by Jeongwoo Lee; Eun Ju Park; Jaewon Choi; Jinho Hong; Sang Eun Shim (pp. 566-574).
The changes of electrical resistance of the polymer composites on exposure to chemical vapors have been applied for the production of vapor sensors. In this study, to confirm the ability of elastomer as chemical vapors sensors, polyurethane/PEG-modified MWCNT composite film was prepared by in situ condensation polymerization and solution casting. The responses of this elastomer composite film for various organic vapors (polar and non-polar solvents) were calculated by monitoring the change in the resistance of the composite film when exposed to the organic vapors. The changes of electrical resistance of the composite films were explained on the basis of volume expansion as swelling and polar interaction of various vapors on the composite. Therefore, we were able to interpret the behavior of the polyurethane/PEG-modified MWCNT composite film as a chemical vapor sensor through diffusion, sorption, and permeation coefficients of the polymer film–analyte systems.
Keywords: Chemical vapor sensor; Polyurethane; Carbon nanotube; Composite film; Swelling behavior
Synthesis, characterization, and dc conductivity of hydrogen-bonding dibenzotetrathiafulvalene (DBTTF) based salts
by Y. Kobayashi; A. Suzuki; Y. Yamada; K. Saigo; T. Shibue (pp. 575-583).
The synthesis, characterization, and dc conductivity of organic conductors, 1-[2-(1,3-benzodithiol-2-ylidene)-1,3-benzodithiol-5-yl]ethylammonium tetrafluoroborate ([DBTTFCH(Me)NH3+]BF4−) and 1-[2-(1,3-benzodithiol-2-ylidene)-1,3-benzodithiol-5-yl]ethylammonium bromide ([DBTTFCH(Me)NH3+]Br−) salts are presented. These salts are prepared by mixing the corresponding primary amine and Brønsted acid in a one-to-one ratio without electrochemical oxidation. The change in the electronic state of insulating DBTTFCH(Me)NH2 into conductive [DBTTFCH(Me)NH3+]X− (X=BF4 and Br) salts and the carrier generation upon salt formation were confirmed by diffuse reflectance (UV–vis) and ESR spectra. The concentration of localized radicals is estimated to be 1 radical/3.3 units and 1 radical/1.8 units for BF4 and Br salts, respectively. The possible carrier generation mechanism is proposed by1H NMR and ESI-TOF-MS spectroscopic analyses. The dc conductivity and the activation energy are σrt=2.3×10−3S/cm with 0.24eV for the BF4 salt, and σrt=1.3×10−3S/cm with 0.21eV for the Br salt.
Keywords: Hydrogen-bonding salt; DBTTF; Protic doping; Carrier generation
Synthesis of vertically-aligned carbon nanotubes on stainless steel by water-assisted chemical vapor deposition and characterization of their electrochemical properties
by Byungwoo Kim; Haegeun Chung; Kyo Seon Chu; Ho Gyu Yoon; Cheol Jin Lee; Woong Kim (pp. 584-587).
We demonstrate synthesis of carbon nanotubes on stainless steel by water-assisted chemical vapor deposition using an Al/Fe bimetallic catalyst. A forest of vertically-oriented carbon nanotubes with a length of a few hundreds of micrometers were grown on the substrates. Electrical measurement confirmed that the carbon nanotubes were electrically connected to the stainless steel. Owing to the carbon nanotubes, electrochemical properties such as faradaic current and electron transfer were considerably improved. Carbon nanotubes grown on the stainless steel substrates would potentially be useful for various applications including electrochemical energy conversion and storage.
Keywords: Carbon nanotubes; Chemical vapor deposition; Stainless steel; Cyclic voltammetry
Synthesis and dispersion of polypyrrole nanoparticles in polyvinylpyrrolidone emulsion
by Hak-Young Woo; Woo-Gwang Jung; Dae-Woo Ihm; Jin-Yeol Kim (pp. 588-591).
Monodisperse particles of conducting polypyrrole (PPy) were directly synthesized in large quantities by emulsion polymerization with FeCl3 in organic solvents in the presence of polyvinylpyrrolidone (PVP). The particles were almost spherical form capped with PVP and their sizes ranged from 30 to 60nm with a narrow size distribution when molecular weight of PVP was 3700k. The particle sizes were decreased with an increase in molecular weight of PVP: as molecular weight is increased from 40k to 3600k, the size is decreased from 90–110 to 60–80nm, respectively. These PPy particles are easily dispersed in organic solvents such as water, methanol, butanol isopropanol and these solutions can also be blended with organic binder polymers by casting for film formation. The conductivity of pelletized PPy particles was 10–15S/cm.
Keywords: Polypyrrole; Nanoparticle; Polyvinylpyrrolidone; Emulsion polymerization
Polypyrrole/vermiculite nanocomposites via self-assembling and in situ chemical oxidative polymerization
by Chao Yang; Peng Liu; Jinshan Guo; Yunpu Wang (pp. 592-598).
Conductive polypyrrole (PPy) was chemically grafted from the self-assembled monolayer (SAM) coated on expanded vermiculite (VMT), resulting in PPy/VMT nanocomposites after VMT particles were surface modified. X-ray diffraction (XRD) analysis confirmed that the main peaks of PPy/VMT nanocomposites are similar to the SAM–VMT particles, which reveal that the crystal structure of SAM–VMT is well maintained after the coating process under polymerization conditions and exhibit semi-crystalline behavior. Thermogravimetric analysis shows that the thermal stability of PPy/VMT nanocomposites was enhanced and these can be attributed to the retardation effect of amine-functionalized VMT as barriers for the degradation of PPy. The morphology of PPy/VMT nanocomposites showed the sheet structure and encapsulated morphology. The composites possess high electrical conductivity at room temperature, weakly temperature dependence of the conductivity.
Keywords: Polypyrrole; Vermiculite; Self-assembled monolayer; Encapsulated structure; Temperature dependent conductivity
Optical and electrochemical investigation of diaminonaphthalene derivatives
by Guojie Wang (pp. 599-603).
A series of diaminonaphthalene derivatives with naphthalene as a core and butylamino and phenylamino as substituted groups were synthesized and their optical and electrochemical behavior were investigated. Phenylamino substituted naphthalene derivatives exhibit two absorption bands, which are assigned to n→π* electronic transitions that are due to electron transfer from nitrogen lone pairs to the π* orbital of the naphthalene group and the phenyl group, respectively. Comparing with butylamino substitutes, phenylated ones exhibit a red-shift in both absorption and emission for their electron-donating phenyl groups. The fluorescence quantum yields of the molecules were measured in THF. Cyclic voltammetric measurements demonstrated that the diaminonaphthalene derivatives possess two oxidation processes and the solid-state ionization potentials were estimated from the electrochemical potential. The phenylamino-naphthalenes possess higher ionization potentials than those of the alkylated ones. The relative HOMO and LUMO levels for these materials, important parameters for the design of efficient organic light-emitting or photovoltaic devices, were assessed through electrochemical and spectroscopic measurements.
Keywords: Naphthalene derivatives; Optical properties; Electrochemistry
Nanoscale photoluminescence of light-emitting poly (3-methylthiophene) nanotubes hybridized with Au nanoparticles
by Dong Hyuk Park; Young Ki Hong; Mi Suk Kim; Eun Hei Cho; Won Jun Choi; Kyung Ho Kim; Q.-Han Park; Dae-Chul Kim; Hugeun Song; Jeongyong Kim; Jinsoo Joo (pp. 604-608).
We reported on the fabrication and nanoscale luminescence characteristics of the hybrid nanotubes (NTs) of light-emitting poly (3-methylthiophene) (P3MT) NT with gold (Au) nanoparticles (NPs) (P3MT/Au-NPs). After hybridizing the Au-NPs onto the surface of P3MT NTs, the light-emitting color of P3MT NTs was dramatically changed from a green to a bright red. From laser confocal microscope photoluminescence (PL) experiments for an isolated single strand of the NTs, we observed a ∼220 times enhancement of the PL peak intensity for the hybrid NT of P3MT/Au-NPs compared to that of the P3MT single NT. The enhancement PL efficiency of the hybrid NT of P3MT/Au-NPs can be explained in terms of a surface plasmon resonance (SPR) and nanoscale local electric field enhancement effects.
Keywords: Hybrid nanotube; Poly (3-methylthiophene); Au nanoparticle; Laser confocal microscope; Photoluminescence; Surface plasmon resonance; Local field enhancement
Environmental responses of polyaniline inverse opals: Application to gas sensing
by Ling-Yueh Yang; Wen-Bin Liau (pp. 609-614).
Much attention has been directed toward the fabrication of nanostructured polyaniline and its applications. In this study, we examined the potential of polyaniline inverse opals as sensors. The inverse opals were chemically synthesized via templating polystyrene colloidal crystals and then subjected to four response tests: dry gas flow, ethanol vapor, hydrogen chloride, and ammonia. The three-dimensionally ordered macroporous polyaniline was of good quality as observed by scanning electron microscopy. The samples demonstrated high sensitivity and fast response to different conditions, which may be due to the porosity facilitating diffusion and large surface area interacting with substances. Moreover, the effect of the structural order on the responses is discussed.
Keywords: Colloidal crystal templating; Polyaniline; Sensors; Three-dimensionally ordered macroporous materials
Pure red electroluminescence from novel heteroleptic cyclometalated platinum(II) emitters embedded in polyvinylcarbazole
by Hidetaka Tsujimoto; Yoshiaki Sakurai; Shigeyuki Yagi; Yuichiro Honda; Hotaka Asuka; Hiroto Terao; Takeshi Maeda; Hiroyuki Nakazumi (pp. 615-620).
We fabricated molecularly doped, polymer-based light-emitting diodes possessing a single emitting layer containing a hole-transporting host polymer poly(N-vinylcarbazole) and an electron-transporting auxiliary, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, doped with novel phosphorescent cyclometalated Pt(II) complexes bearing arylpyridine and 1,3-diketone ligands. These novel cyclometalated Pt(II) complexes emit pure red color both in steady-state emissions (poly(methyl methacrylate) films)) and electrophosphorescence. They exhibited pure red emissions with the Commission Internationale de l’Eclairage coordinates ( X=∼0.67, Y=∼0.33), which is almost identical to the coordinates of standard red (0.66, 0.34) demanded by the National Television System Committee. The color coordinates remained unchanged over a range of operating voltages, even at luminances greater than 1×104cd/m2. The maximum external quantum efficiency of these devices exceeded 3.6% and the maximum brightness was greater than 1×104cd/m2.
Keywords: Polymer light-emitting diodes; Heteroleptic cyclometalated platinum(II) complex; Photoluminescence; Pure red electrophosphorescence; Polyvinylcarbazole
Effect of Ag nanoparticles on the electron energy structure and electrical properties of poly( p-phenylene vinylene) (PPV)
by Cho-Young Lee; Yong-June Choi; Sook Yoon; Hyung-Ho Park (pp. 621-624).
The effects of inorganic nanoparticles on a conjugated polymer were investigated by measuring the electronic properties of poly( p-phenylene vinylene) (PPV) and PPV/Ag nanocomposites. Through hybridization, an enhancement in current density was achieved with PPV/Ag nanocomposites due to an increase in the electron affinity with Ag nanoparticle content. Furthermore, roughening of the surface morphology was observed with incorporation of Ag nanoparticles. This roughness induces an enhanced applied field at the thinner region of the film and an increase in the surface area with a resulting increase of electron injection, leading to current enhancement.
Keywords: PPV; Ag nanoparticles; Composite film; Electron energy structure
Synthesis, spectroscopy and electroluminescence of cadmium(II) polypyridyl complexes
by Xuegang Chen; Yuanqiang Ding; Yanxiang Cheng; Lixiang Wang (pp. 625-630).
Five new complexes [Cd(ptpy-R)2](PF6)2 (ptpy=4′-phenyl-2,2′:6′,2″-terpyridine; R=tert-Butyl (1), hexyloxy (2), carbozole-9-yl (3), naphthalene-1-yl-phenylamine-N-yl (4) and diphenylamine-N-yl (5)) were synthesized and characterized by1H NMR, elemental analyses, UV–vis spectroscopy and cyclic voltammetry. The emission color of resultant complex molecules has been tuned effectively, from violet (397nm) for1 to orange (602nm) for5 in film, by modifying the electron-donating ability of the substituent R. The UV–vis spectroscopy and the solution-state luminescence showing remarkable solvatochromism suggests the emission involves the intra-ligand charge transfer (1ILCT) excited state, occurring from the substituent R moiety to Cd(II) coordinated terpyridine. The electroluminescence (EL) properties for these organic materials were also studied and complexes3,4 and5 exhibit EL wavelength at 548nm, 596nm and 604nm with maximum current efficiency of 3.25cd/A, 3.15cd/A and 2.16cd/A, respectively.
Keywords: Cadmium polypyridyl complexes; Spectroscopy properties; Solvatochromism; Electroluminescence
Small molecule host system for solution-processed red phosphorescent OLEDs
by Kyeong Heon Kim; Jae Yeol Lee; Tae Jin Park; Woo Sik Jeon; G.P. Kennedy; Jang Hyuk Kwon (pp. 631-635).
We demonstrate high efficiency solution-processed red phosphorescent OLEDs with small molecule mixed host systems. 2-TNATA (4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine):TPBI (2,2′,2″-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole)) and m-MTDATA (4,4′,4″-tri-(N-3-methylphenyl-N-phenylamino)triphenylamine):TPBI host systems are reported as good soluble mixed host systems. A doping level of 3% bis(2-phenylquinoline)(acetylacetonate)iridium (Ir(phq)2acac) dopant in the 2-TNATA:TPBI (1:1 ratio) mixed host produces the best quantum efficiency and driving voltage. This fabricated red phosphorescent OLED has a driving voltage of 5.2V and maximum current and power efficiencies of 17.8cd/A and 11.3lm/W, respectively. Minimal electron or hole trapping in the phosphorescent dopant molecules and prevention of self quenching by the low doping technique appear to be the key reasons for good device performance.
Keywords: Phosphorescent; OLED; Host; Red
Effects of small octahedral mono, di, and trivalent hexafluoroanions on electronic and molecular structures of polypyrrole monitored by in situ UV–vis–NIR and resonance Raman spectroelectrochemical measurements
by Maria Grzeszczuk; Anna Kępas; Carita Kvarnstrom; Ari Ivaska (pp. 636-642).
In situ UV–vis–NIR and Raman spectra were recorded for three polypyrroles of different compositions established by the specific redox responses of the polymers. Polypyrrole has been electrodeposited in the reversibly oxidized state and concomitantly doped with a small octahedral counterion from aqueous solution of sodium hexafluorophosphate, sodium hexafluorosilicate or sodium hexafluoroaluminate. The dopant anions differ from each other by the charge valency, having at the same time very similar ionic radii. The spectra of the resulting three polypyrroles were found to differ noticeably. An origin of the differences was discussed. The doping level and/or structure of a polymer phase can be invoked to explain the observed spectral changes of the polymer due to the anion dopants. As expected, the most counterion sensitive are the N–H bond and the polaron and bipolaron electronic levels. Polypyrrole doped with hexafluoroaluminate has generated the spectra that differ markedly from that recorded for polypyrrole hexafluorosilicate and polypyrrole hexafluorophosphate. The spectroscopic results are in agreement with earlier findings concerning electrochemical properties of polypyrrole hexafluoroaluminate and polypyrrole hexafluorosilicate. Raman bands that are usually assigned to the ring deformation vibrations were shown to decrease significantly in energy on oxidation of polypyrrole (900–1000cm−1). Raman bands intensities are complex function of laser energy and electrode potentials so their analysis on the anion effects should be performed rather at a constant length of laser excitation.
Keywords: UV–vis–NIR spectroelectrochemistry; Raman spectroelectrochemistry; Polypyrrole in aqueous environment; Hexafluoranions of Al(III); Si(IV), and P(V)
Dipole assisted exciton dissociation at conjugated polymer/fullerene photovoltaic interfaces: A molecular study using density functional theory calculations
by C.F.N. Marchiori; M. Koehler (pp. 643-650).
Using density functional theory calculations we probe the electronic structure of the P3HT/fullerene supramolecule. Our simulations indicates that the mix of the polymer and fullerene wave functions give rise to a set of intragap charge transfer (CT) states at the polymer/fullerene interface. This overlap of wavefuctions produces a charge transfer in the ground state. The interaction between this effect and the permanent dipole in the polymer creates a dipole across the supramolecule pointing from the fullerene to the polymer. We find that an efficient exciton dissociation is possible because (i) the CT states are energetically favorable intermediary levels for the electron transfer from the polymer to the fullerene; (ii) there is a potential energy barrier height that blocks the hole transfer to the P3HT chain of the complex, keeping the charge carrier confined in the chain next to the P3HT/fullerene system. This barrier is created by the potential energy of the supramolecule’s dipole moment immersed in the electric field of the electron–hole pair. Finally, using a simple analytical model we show that the dipole’s induced barrier height depends critically on the orientation of the dipole vector relative to the polymer backbone. From this analysis we anticipate the main features of a conjugated polymer/fullerene complex with a high efficiency on exciton dissociation.
Keywords: PACS; 73.20.; −; r; 71.15.Mb; 71.20.TxOrganic photovoltaics; Exciton dissociation; Donor/acceptor complexes
Ellipsometric study on the optical property of UV exposed MEH-PPV polymer film
by Y.W. Jung; J.S. Byun; Y.H. Cha; Y.D. Kim (pp. 651-654).
We performed ellipsometric analysis on the effect of Ultra-Violet (UV) light exposure to the poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV) films. The measured dielectric function spectrum of the MEH-PPV film showed the consistent decrease of absorption coefficients with the UV light exposure time, especially at the ordinary axis. This work notes that UV light protection method should be included in the process of MEH-PPV films for the optical device applications to prevent the significant change of optical property of the film and to maintain its efficient absorption of sunlight for solar cell devices.
Keywords: Ellipsometry; MEH-PPV; Solar cell; Anisotropy; Optical property
Enhanced capacitance textile fibres for supercapacitors via an interfacial molecular templating process
by Gregory J. Wilson; Mark G. Looney; A.G. Pandolfo (pp. 655-663).
The application of poly(2-methoxyaniline-5-sulfonic acid), PMAS, as a molecular template in a bi-layered co-polymerisation process onto a microporous activated carbon fibre is presented. This process produces a bound, compact molecular layer of PMAS, onto which polyaniline (PAni) or polypyrrole (PPy) is co-polymerized as a thin permeable layer coating the surface of the carbon fibre. The physical porous structure of the coated carbon fibre is examined via multi-point isothermal N2 adsorption at 77K. Surface area and porosity data, calculated using BET and Density Functional Theory (DFT) models, indicates that the majority of the microporosity of the activated carbon fibre is still accessible after polymer deposition. Voltammetry and impedance data, in an aqueous electrolyte (1M H2SO4), is presented to show the enhancement of the capacitance and resistance properties of the composite material and the benefit of these improvements to its use as a supercapacitor electrode material. Formation of the bi-layer carbon fibre composite resulted in an effective increase in capacitance; from 125Fg−1 for the untreated carbon substrate, to as high as 222Fg−1 for the PAMS/PAni treated sample. The latter result represents a 69% improvement in capacitance and is attributed to the additional pseudocapacitive contribution of the ECP and the preservation of double-layer capacitance through the retention of fibre microporosity. Impedance analysis of the PMAS/PAni composite sample estimates the materials’ intrinsic resistance to be R s=3.7Ω and distributed pore resistances (ΩDPR) of 2.8Ω; compared to R s=1.8Ω and ΩDPR=6.4Ω for the untreated carbon substrate.
Keywords: EDLC; Ultracapacitor; Asymmetric supercapacitor; Activated carbon; Electrically conducting polymer; Carbon fibre
Morphological development of nanofibrillar composites of polyaniline and carbon nanotubes
by Ana López Cabezas; Zhi-Bin Zhang; Li-Rong Zheng; Shi-Li Zhang (pp. 664-668).
Nanofibrillar composite of polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) is readily synthesized by means of conventional in situ polymerization process. It is found that the MWNT loading during polymerization has a significant influence on both the micro- and macro-scale morphological properties of the composites. At low MWNT loadings, PANI/MWNTs are formed as individual nanofibers, similar to that of the neat PANI in the absence of MWNTs. With the increase in MWNT loading, the composite exhibits granular form and becomes a continuous porous matrix at higher MWNT loadings. A possible mechanism is proposed to account for the structural variation of the composites caused by MWNTs at the different loadings.
Keywords: Composite; Carbon nanotubes; Polyaniline; Conducting polymers
Electrochemical performance of a high cation-deficiency Li2Mn4O9/active carbon supercapacitor in LiNO3 electrolyte
by Yan Jing Hao; Qiong Yu Lai; Ling Wang; Xiao-Yun Xu; Hong Yan Chu (pp. 669-674).
A hybrid supercapacitor based on spinel Li2Mn4O9 and activated carbon (AC) was fabricated. The electrochemical performance of the capacitor was studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge in different aqueous electrolytes such as 1M LiNO3, Li2SO4, NaNO3 and KNO3 solution. A maximum specific capacitance of 261Fg−1 was obtained for the Li2Mn4O9 single electrode between 0 and 1.4V. The Li2Mn4O9/AC hybrid supercapacitor showed a sloping voltage profile from 0 to 1.4V and delivered an energy density of 53Whkg−1 based on the total weight of the active electrode materials. The hybrid capacitor exhibited a desirable profile and maintained over 80% of its initial energy density after 1000 cycles, indicating that Li2Mn4O9 has excellent cycling performance and structural stability in aqueous electrolyte. The hybrid supercapacitor also exhibited an excellent rate capability, even at a power density of 1250Wkg−1, it had a specific energy 29Whkg−1 compared with 48Whkg−1 at the power density of about 417Wkg−1.
Keywords: Supercapacitor; High cation-deficiency spinel Li; 2; Mn; 4; O; 9; Activated carbon; Aqueous electrolyte; Lithium-ion intercalated compound
Highly efficient bilayer blue phosphorescent organic light-emitting devices
by Tae-Yong Kim; Dae-Gyu Moon (pp. 675-677).
We have developed highly efficient blue phosphorescent organic light-emitting devices comprising of two organic layers. Hole transporting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) was used as an emitting host for iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato- N, C2′]picolinate (FIrpic) guest. In our bilayer system, the host–guest energy transfer process leads to a low optimal doping concentration of 2wt%, while the better charge balance is achieved by the better electron injection into the host layer from electron transport layer. Using these bilayer structures, we demonstrate a maximum current efficiency of 34cd/A in the device structure of ITO/TAPC: FIrpic (30nm, 2wt%)/3-(4-biphenyl-yl)-4-phenyl-5-(4- tert-butylphenyl)-1,2,4-triazole (50nm)/LiF/Al.
Keywords: Organic light-emitting device; Phosphorescence; Blue; Bilayer
A facile synthesis and characterization of semiconducting p-phenylenediamine–aniline copolymer
by M. Rani; R. Ramachandran; S. Kabilan (pp. 678-684).
Synthesis of p-phenylenediamine ( p-PDA)-aniline copolymer was carried out using K2S2O8 and (NH4)2S2O8 as an oxidizing agent. Of the two, K2S2O8 was found to be the best oxidizing agent and the newly synthesized copolymer was characterized by UV–visible, FT-IR, fluorescence, proton NMR, cyclic voltammetry, solubility and SEM studies. Conductivity studies of the same with different dopants were also made and found to fall in the region of semiconductor. Morphological study revealed that the neutral copolymer forms into less regular and amorphous structure.
Keywords: p; -Phenylenediamine; Aniline; Copolymer; Conductivity
Synthesis, characterization and magnetic properties of polyaniline-magnetite nanocomposites
by A.C.V. de Araújo; R.J. de Oliveira; S. Alves Júnior; A.R. Rodrigues; F.L.A. Machado; F.A.O. Cabral; W.M. de Azevedo (pp. 685-690).
In this work we report a new and straightforward method to prepare the polyaniline-magnetite nanocomposite PANI-Fe3O4. The method utilizes Fe3O4 nanoparticles as the oxidizing agent assisted by UV light to synthesize PANI-Fe3O4 magnetic nanocomposite. FTIR and XRD analyses confirm that polyaniline has been obtained in the emeraldine salt form and that the mean diameter of the Fe3O4 nanoparticles before synthesis was of the order of 25nm; for the PANI-Fe3O4 nanocomposite in HCl after 4h of reaction, the mean diameters were of the order of 11nm. Also, feroxyhite was detected as a secondary phase for the nanocomposite. The dc conductivity results for the pure magnetite were about 2.4×10−6Scm−1, while the nanocomposites were of the order of 10−5Scm−1, confirming the increase in conductivity with the increasing amount of PANI. The magnetic measurements showed ferromagnetic behavior for the nanoparticles, with high-saturated magnetization ( M S=74.30emug−1) and a coercive force of 93.40Oe. In addition, it was observed that the saturated magnetization for the nanocomposite strongly depends on the reaction time under UV irradiation.
Keywords: Polyaniline; Iron oxide; Nanoparticles; Nanocomposites
Deep blue organic light-emitting diodes based on triphenylenes
by Henning Wettach; Stefan S. Jester; Alexander Colsmann; Uli Lemmer; Nina Rehmann; Klaus Meerholz; Sigurd Höger (pp. 691-700).
We report about new easy-to-synthesize deep blue light-emitting organic materials. Various substituted low-molecular-weight triphenylene-derivatives have been prepared in a one-step procedure and are easily available on large scale and high purity. Furthermore, the synthesis of an oxetane functionalized, photo-crosslinkable triphenylene-based emitter material with enhanced film-forming properties is described. The low-molecular-weight emitters were vacuum-deposited, whereas the photo-crosslinkable emitter material derivative was processed from solution. The optical and electrical properties of the compounds were investigated. The corresponding photoluminescence emission spectra exhibit λmax,ems values around 400nm. Organic light-emitting multi layer devices were fabricated and characterized. OLED devices from these molecules emit deep blue light of 436–456nm.
Keywords: OLEDs; Triphenylenes; Blue light-emitting; Vacuum processing; Solution processing
Polypyrrole and polyaniline prepared with cerium(IV) sulfate oxidant
by Mária Omastová; Katarína Mosnáčková; Miroslava Trchová; Elena N. Konyushenko; Jaroslav Stejskal; Pavol Fedorko; Jan Prokeš (pp. 701-707).
The conducting polymers, polypyrrole and polyaniline, were synthesized by chemical oxidative polymerization of the corresponding monomers in 0.1M sulfuric acid using cerium(IV) sulfate as the oxidant at mole ratios of oxidant-to-monomer ranging from 0.5 to 3. The yields of the oxidation products were determined, and the samples were characterized with respect to their elemental composition, molecular structure, and morphology. The conductivity of polypyrrole prepared in 0.1M sulfuric acid, 10−1 to 100Scm−1, was higher compared with the conductivity of polyaniline prepared under the same conditions, 10−3 to 10−1Scm−1. The loss of mass after deprotonation with ammonium hydroxide is reported, and discussed in terms of the type of protonation as also reflected by FTIR spectroscopy. The conductivity of polypyrrole bases remained at relatively high level, 10−5 to 10−3Scm−1, while PANI bases became non-conducting, 10−12 to 10−10Scm−1. The polymers had a granular morphology in all cases.
Keywords: Polypyrrole; Polypyrrole base; Polyaniline; Cerium(IV) sulfate; Conducting polymer
Preparation, FTIR spectroscopic characterization and isothermal stability of differently doped conductive fibers based on polyaniline and polyacrylonitrile
by Asif Ali Khan; Mohd Khalid (pp. 708-712).
Conductive fibers based on polyaniline (PANI) and polyacrylonitrile (PAN) were obtained by stirring with magnetic bar. This research was conducted to investigate conducting fibers of polyaniline:polyacrylonitrile (PANI:PAN) composite with different weight ratios of aniline in PAN matrix. The fibers were prepared by stirring process. The best conductivity behavior of the fibers was obtained with 5mL of aniline. The fibers obtained were characterized using Fourier-transform infrared spectra (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The variation of electrical conductivity with different type doping agents (HCl, H2SO4 and HClO4) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.
Keywords: Conducting polymer; Electrical conductivity; Thermal stability
A paddlewheel dinuclear Cu(II) compound coordinated with TTF-py redox ligand
by Qin-Yu Zhu; Yu Liu; Zhe-Jun Lu; Jin-Po Wang; Li-Bin Huo; Yu-Rong Qin; Jie Dai (pp. 713-717).
A new paddlewheel dinuclear complex with a pyridyl-tetrathiafulvalene (TTF-py) ligand has been obtained and characterized crystallographically as [(DMT-TTF-py)2Cu2(OAc)4]·2C6H6 (1). Meanwhile a mononuclear compound [(DMT-TTF-py)2Cu(PhCOO)2(CH3OH)2]·2CH2Cl2 (2) was also isolated. UV–vis spectra and cyclic voltammogram of the paddlewheel complex were studied, showing that compound1 can undergo an oxidization to form a stable cation of [(DMT-TTF-py)2Cu2(OAc)4]2+. By this strategy, compound3, [(DMT-TTF-py)2Cu2(OAc)4](I3)2 as a radical salt, has been prepared and its conductivity of powder sample was 1.02×10−3ohm−1cm−1. Antiferromagnetic coupling of Cu(II)–Cu(II) was found from the results of ESR spectra, but the coupling between the radical–Cu(II) was very weak.
Keywords: Tetrathiafulvalene; Copper complex; Radical compound; Magnetic coupling; Redox ligand
High photoluminescence and photoswitch of bis(8-hydroxyquinoline) zinc nanoribbons
by Xiuhua Wang; Mingwang Shao; Li Liu (pp. 718-721).
Highly luminescent bis(8-hydroxyquinoline) zinc nanoribbons with average width of 150nm and thickness of 50nm and length up to several hundreds of micrometers have been synthesized via a facile solvothermal method. The room-temperature photoluminescence spectrum of the products showed a strong and stable emission centered at 515nm under excitation at 386nm. The nanoribbons were found to be sensitive to light. The photocurrent enhanced by ca. 24 times under irradiation of an incandescence lamp with power density of 2.5mW/cm2. This conclusion was interesting and might found potential application in light-controlled devices in the future.
Keywords: Bis(8-hydroxyquinoline) zinc; Nanoribbons; Photoluminescence; Photoswitch
Pure exciplex electroluminescence in blended film of small organic molecules
by Pabitra K. Nayak; Neeraj Agarwal; N. Periasamy; Meghan P. Patankar; K.L. Narasimhan (pp. 722-727).
3,6-diarylcarbazole derivatives, 3,6-di-(p-cyanophenyl)-N-hexylcarbazole (CNHC) and 3,6-di-(p-acetylphenyl)-N-hexylcarbazole (ANHC) were synthesized, characterized and energy levels determined. Steady state fluorescence of these molecules showed blue emission in thin films. Blends of these molecules with N,N′-diphenyl-N,N′-(bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) showed exciplex emission as the dominant one. Single layer organic light emitting devices (OLEDs) of CNHC, ANHC and their blends with TPD were fabricated using ITO as anode and Ca as cathode. The blend film devices showed pure exciplex electroluminescence.
Keywords: OLED; Electroluminescence; Exciplex; Blend film
Enhanced electrical conductivity of polyaniline film by a low magnetic field
by Jae-Kook Park; O-Pil Kwon; Eun-Young Choi; Chan-Keun Jung; Suck-Hyun Lee (pp. 728-731).
We report the enhanced electrical conductivity of polyaniline (PANI) films produced in a low magnetic field using polyaniline that was synthesized by a self-stabilized dispersion polymerization (SSDP). The sample PANI film prepared with a low magnetic field of 1.4T showed a 1.85-fold increase in electrical conductivity. Moreover, the film using the polyaniline prepared using the SSDP method showed greater conductivity enhancement than the conventionally prepared sample. In addition, the PANI films exhibited considerable anisotropy of the electrical conductivity depending on the direction of the applied magnetic field. This was attributed to the non-negligible contribution of the orientation of the polyaniline backbone segment and the face-to-face π–π stacking of the main-chains by the magnetic field.
Keywords: Polyaniline; Conducting polymers; Magnetic field; Electrical conductivity
Fabrication of Pt nanoparticles decorated PPy–MWNTs composites and their electrocatalytic activity for methanol oxidation
by Bo Qu; Yi-Ting Xu; Su-juan Lin; Yi-Fang Zheng; Li-Zong Dai (pp. 732-742).
Here we report the synthesis and characterization of a catalyst material constituted of Pt, polypyrrole (PPy) and multi-walled carbon nanotubes (MWNTs). The catalyst supports (PPy–MWNTs nanocomposites) were synthesized via in situ chemical polymerization in advance, in which MWNTs were regarded as the matrix material. The supports were characterized by SEM & TEM, elemental analysis, XRD, FTIR and conductivity measurements. Then the catalysts were synthesized by a chemical reduction using sodium borohydride (NaBH4) as reducing agent and acetic acid buffer (pH=4) containing trace K2C2O4 as reaction media. FTIR spectra showed that there existed relations between PPy and MWNTs during in situ polymerization. SEM and TEM micrographs of the catalyst samples exhibited that the existence of PPy layer which was evenly wrapped on the surface of MWNTs resulted in significant improvement in helping Pt particles well dispersed. XRD results showed that higher Pt(111) content in the catalyst deposited on PPy–MWNTs supports than that on MWNTs. The cyclic voltammetry (CV) tests of methanol electrocatalytic oxidation demonstrated that the electrode modified by Pt/PPy–MWNTs ternary composite catalyst showed higher catalytic stability than Pt/MWNTs binary catalyst, due to the synergic interaction between Pt and the carrier.
Keywords: Polypyrrole; Mutil-wall carbon nanotubes; Pt catalysts; Methanol electrocatalytic oxidation; CO anti-poisoning
Structure, DC and AC conductivity of oxazine thin films prepared by thermal evaporation technique
by A.A.M. Farag; F.S. Terra; G.M. Mahmoud (pp. 743-749).
Thin films of oxazine (OXZ) were prepared using thermal evaporation technique under high vacuum. The thermogravimetric analysis (TGA/DSC) was investigated. Thin films of nano-crystalline OXZ were identified by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Temperature dependence of the DC electrical conductivity was investigated in the temperature range 300–425K. Measurements revealed that the DC behavior of the films can be described by Mott's one-dimensional variable range hopping (VRH) model in the entire temperature range. The AC conductivity of the sample is found to be proportional to ω s. The temperature dependence of the AC conductivity and the frequency exponent, s is reasonably well interpreted in terms of the correlated barrier-hopping CBH model. Frequency dependence of the capacitance in the frequency range 42Hz–5MHz indicates that the capacitance is strongly frequency dependent. The capacitance was determined to decrease with increasing frequency at low frequency and less rapidly at higher frequencies. This is quantitatively interpreted using an equivalent circuit model.
Keywords: DSC; TGA; DC conductivity; AC conductivity; Oxazine
Phenyl-, carbazolyl- and fluorenyl-substituted derivatives of indolo[3,2- b]carbazole as hole-transporting glass forming materials
by M. Kirkus; J. Simokaitiene; J.V. Grazulevicius; V. Jankauskas (pp. 750-755).
A series of new derivatives of indolo[3,2- b]carbazole containing phenyl, fluorenyl and carbazolyl substituents at the nitrogen atoms were synthesized by Ullmann coupling of 6-pentyl-5,11-dihydroindolo[3,2- b]carbazole with the different aryl halogenides. The optical, photophysical, photoelectrical and thermal properties of the materials obtained were studied. All the synthesized compounds can be transformed into the amorphous phase with the glass transition temperatures ranging from 0 to 154°C. The ionization potentials of the newly synthesized derivatives of indolo[3,2- b]carbazole are in the range of 5.22–5.48eV. The lowest energy absorption edges and the lowest ionization potentials were observed for carbazolyl-substituted derivatives. Charge transport properties of the synthesized materials were estimated by the time-of-flight technique. The highest hole drift mobilities were observed for the fluorenyl-substituted derivative. For the molecular glass of 5,11-bis(9,9-dibutyl-9 H-fluoren-2-yl)-6-pentyl-5,11-dihydroindolo[3,2- b]carbazole they exceed 10−3cm2/Vs at an electric field of 3.6×105V/cm.
Keywords: Indolo[3,2-; b; ]carbazole; Molecular glass; Ionization potential; Hole drift mobility
White electroluminescence from stacked organic light emitting diode
by Priyanka Tyagi; Ritu Srivastava; Arunandan Kumar; Virendra Kumar Rai; Rakhi Grover; M.N. Kamalasanan (pp. 756-761).
Electroluminescent zinc complex [(2-(2-hydroxyphenyl)benzoxazole)(2-methyl-8-hydoxyquinoline)] zinc [Zn(hpb)mq] has been synthesized. It has been used with a blue emitting zinc complex Zn(hpb)2, to fabricate stacked organic light emitting diode (OLED). Thickness of layers of these materials has been optimized to achieve white light emission. The maximum luminescence of the device was 8390Cd/m2 at 14V. Commission Internationale de l’Eclairage coordinates of the device, with 40nm thickness of Zn(hpb)2 and 15nm thickness of Zn(hpb)mq, were (0.29, 0.38) at 7V and were well within the white region. A model has been presented for simulating the electroluminescence (EL) spectrum of stacked OLED based on Gaussian disorder model using Monte-Carlo technique. From the model the energetic disorders, highest ocuppied molecular orbital and lowest unoccupied molecular orbital positions of different emissive layers and the excimer layer have been estimated.
Keywords: Electroluminescence; SOLED; Monte-Carlo simulation; Gaussian DOS
Uniform polyaniline microspheres: A novel adsorbent for dye removal from aqueous solution
by Lunhong Ai; J. Jiang; Rui Zhang (pp. 762-767).
Uniform polyaniline (PANI) microspheres were synthesized by a facile polymerization of aniline monomer in the acidic medium. The structure and morphology of PANI microspheres were characterized by means of FTIR spectrometer, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Adsorption characteristics of PANI microspheres were examined using methyl orange (MO) as adsorbate. Batch adsorption experiments were carried out to investigate adsorption kinetics and isotherms of PANI microspheres. Adsorption equilibrium studies showed that MO adsorption followed Freundlich model. The adsorption kinetics was best described by pseudo-second-order model. The results indicated that PANI microspheres can be used as a novel, effective and low-cost adsorbent material for dye removal.
Keywords: Polyaniline; Microsphere; Adsorption; Dye removal
Polypyrrole/conductive mica composites: Preparation, characterization, and application in supercapacitor
by Chao Yang; Peng Liu (pp. 768-773).
Polypyrrole/conductive mica (PPy/CM) composites were prepared by coating polypyrrole (PPy) onto the surfaces of the conductive mica (CM) via the in situ chemical oxidative polymerization method. The encapsulating morphologies were revealed with the scanning electron microscopy (SEM) technique. The PPy/CM composites were characterized with Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The composites possess high electrical conductivity at room temperature, the weak temperature dependence of the conductivity. Based on the cyclic voltammetry and the charge/discharge behavior of the PPy/CM composites, it was found that the composites performed typical electrochemical supercapacitor behavior.
Keywords: Polypyrrole; Conductive mica; Composites; Electrical conductivity; Electrochemical supercapacitor
Field, temperature and thickness dependent electron transport in 5,5′-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole)
by Arunandan Kumar; Ritu Srivastava; Priyanka Tyagi; D.S. Mehta; M.N. Kamalasanan; M. Ananth Reddy; K. Bhanuprakash (pp. 774-778).
Charge transport in 5,5′-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is investigated as a function of temperature and organic layer thickness. The thickness dependence of the current indicates towards the trap charge limited conduction (TCLC) with a field and temperature dependent mobility. The density of trap states has been found to be dependent on sample thickness. As the thickness has increased from 80nm to 120nm, trap energy has correspondingly increased from 78meV to 130meV. TCLC model with Poole Frenkel type field dependent mobility has been fitted into the data and has been found in excellent agreement. Temperature dependency of zero field mobility ( μ0) and β has been estimated from the model.
Keywords: Charge transport; Trap energy; Trap density; TCLC
Improved open circuit voltage of the photovoltaic device using ferrocene as a donor material
by Rakesh A. Afre; Yasuhiko Hayashi; Tetsuo Soga (pp. 779-782).
In this work, we have studied the combination of ferrocene (Fc), the donor material and fullerene derivatives such as [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and the acceptor material, for fabricating organic photovoltaic devices. The effect of temperature on open circuit voltage ( Voc), short-circuit current density ( Jsc), fill factor ( FF) and the photoconversion efficiency ( PCE), η has been investigated. By varying the annealing temperature, the Voc, FF and PCE, η, were increased up to 140°C and further increasing of temperature it remains constant. However, the short-circuit current density was not varied concomitantly with other parameters. The maximum PCE was observed to be 0.053% at 140°C, which is the best annealing temperature in the present study. There have been many attempts to synthesize Fc and fullerene dyads but as an application wise very few report are available. Therefore here we have tried to use Fc and PCBM for photovoltaic device applications.
Keywords: Ferrocene; Fullerene derivative (PCBM); Photovoltaic device
Preparation and characterization of polyaniline micro/nanotubes with dopant acid mordant dark yellow GG
by Li Ren; Xue Feng Zhang (pp. 783-787).
Polyaniline(PANI) micro/nanotubes doped with novel dopant acid mordant dark yellow GG (AMY GG) were prepared by soft template method in the presence of ammonium persulfate (APS) as an oxidant. It was found that the molar ratio of HCl to aniline and washing method of the products played key roles in the formation of PANI micro/nanotubes. Changing the molar ratio of HCl to aniline, the typical morphology of PANI could be changed from nanotubes to microtubes. In order to get the final product, different solvents were tried to wash away the by-products. After the by-products were removed by water/methonal/ether, the PANI micro/nanotubes appeared. The morphology of PANI micro/nanotubes was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical structure and thermal stability of PANI micro/nanotubes were examined by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) and the thermogravimetric analysis (TGA). The formation mechanism of PANI micro/nanotubes was also discussed.
Keywords: Polyaniline; Micro/nanotube; Acid mordant dark yellow GG; Dopant
Improved performance of Si-based top-emitting organic light-emitting device using MoO x buffer layer
by Xiao-Wen Zhang; Jun Li; Liang Zhang; Hua-Ping Lin; Xue-Yin Jiang; Wen-Qing Zhu; Zhi-Lin Zhang (pp. 788-790).
Highly efficient Si-based top-emitting organic light-emitting device (TOLED) using MoO x buffer layer is demonstrated. With tris(8-hydroquinoline) aluminum as emitting and electron-transport layer, the p-Si/MoO x based TOLED shows a maximum luminous efficiency of 1.1cd/A and a power efficiency of 0.68lm/W, which are almost double those (0.64cd/A and 0.34lm/W) of p-Si/SiO2 based TOLED. Moreover, in comparison with the widely used thermally grown SiO2 buffer layer, MoO x can be deposited by conventional evaporation technology and thereby simplifying fabrication process.
Keywords: PACS; 78.60.Fi; 73.40.Lq ;78.66.Qn; 72.80.Cw ;72.80.LeOLED; Top-emitting; Si; Work function; Buffer layer
Mechanically strong conducting hydrogels with special double-network structure
by Tingyang Dai; Xutang Qing; Hui Zhou; Chen Shen; Jing Wang; Yun Lu (pp. 791-796).
Mechanically strong conducting hydrogels composed of poly(acrylamide) (PAAm) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) have been synthesized through the construction of a special double-network (sDN) structure. The novelty of the sDN hydrogels lies in the introduction of PEDOT-PSS semi-interpenetrating polymer network (semi-IPN) hydrogel as the second network. Based on the experimental results and the double-network theory, an additional strengthening effect resulting from the formation of the PEDOT clusters in a three-step fracture process is proposed. The applicability of as-prepared PAAm/PEDOT-PSS sDN hydrogels in electromechanical actuators is also briefly discussed.
Keywords: Hydrogels; Conducting polymers; Special double-network; Mechanical toughness; Electromechanical actuator
Crystal structures and magnetic properties of two molecular solids based on bis(maleonitriledithiolate)nickelate monoanion with substituted piperidinium cations
by Jia-rong Zhou; Xing Chen; Yong Hou; Ying-ying Zheng; Qian Huang; Hong-rong Zuo; Le-min Yang; Chun-lin Ni; Qing-jin Meng (pp. 797-802).
Two new molecular solids, [1-NaMePid][Ni(mnt)2](1) and [2-NaMePid][Ni(mnt)2](2) (mnt2−=maleonitriledithiolate, [1-NaMePid]+=1-(1′-naphthylmethyl)piperidinium and [2-NaMePid]+=1-(2′-naphthylmethyl)piperidinium) have been characterized structurally and magnetically. Both [Ni(mnt)2]− anions and the cations of1 and2 form segregated column stacks, and the Ni(III) ions form a 1D zigzig alternating magnetic chain within a [Ni(mnt)2]− column through Ni···S, S···S, Ni···Ni, or π···π interactions. Some conformational features in two isomeric cations and the geometry of the individual [Ni(mnt)2]− anion for1 and2 remain similar, while the changes of the space filling properties, the packing requirements and the existence of the water molecule in2 result in the difference of the stacking mode of the [Ni(mnt)2]− anions. Magnetic susceptibility measurements in the temperature range 2–300K show that1 is diamagnetism, while2 exhibits a novel and interesting spin–gap transition around 16.8K with antiferromagnetic interaction ( J=−4.6cm−1) in the high-temperature phase (HT) and the spin–gap (Δ/ k b=68.5K) in the low-temperature phase (LT).
Keywords: Bis(maleonitriledithiolate)nickelate(III) anion; Substituted piperidinium; Crystal structure; Overlapping mode; Magnetic properties; Spin–gap transition
Influence of electrochemical doping on low frequency noise of conducting poly(3-methylthiophene) film
by Wenbin Xue; Xiaoqing Jiang; Yutaka Harima (pp. 803-807).
Low frequency noise properties of the poly(3-methylthiophene) film prepared by electrochemical polymerization on two-band Pt electrode are investigated. The relation between flicker noise and conducting properties under different doping potential is discussed on the basis of the Hooge empirical equation. Under light doping state, the Hooge parameter almost remains constant with increasing doping potential. However, in the case of heavy doping, it increases with doping potential. The dependence of the Hooge parameter on doping level reflects the evolution of metallic domains and the transport process of charge carriers. It is believed that the amorphous structure and high carrier concentration in the poly(3-methylthiophene) film lead to a greater Hooge parameter value.
Keywords: Low frequency noise; Poly(3-methylthiophene) film; Hooge parameter; Electrochemical polymerization; Electrochemical doping
Amperometric alcohol biosensors based on conducting polymers: Polypyrrole, poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxypyrrole)
by Özlem Türkarslan; A. Elif Böyükbayram; Levent Toppare (pp. 808-813).
Alcohol biosensors based on conducting polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxypyrrole) (PEDOP) were constructed. Alcohol oxidase (AlcOx, from Pichia pastoris) was immobilized during electropolymerization of the monomers in sodium dodecylsulfate (SDS) and phosphate buffer electrolysis medium. Optimization of several parameters was carried out. The highest affinity was observed for the PEDOT/AlcOx sensor. Lowry protein determination method was also used to calculate the amount of immobilized enzyme in sensors. Before testing the biosensors on alcoholic beverages effects of interferents (glucose, acetic acid, citric acid, andl-ascorbic acid) were determined. The alcohol contents of the distilled beverages (vodka, dry cin, whisky, and rakı) were determined with the sensors constructed. A good match with the chromatography results was observed.
Keywords: Amperometric biosensor; Alcohol sensor; Alcohol oxidase; Conducting polymers
Polypyrrole-carbon nanotube composite films synthesized through gas-phase polymerization
by Yeon-Kyeong Lee; Keum-Ju Lee; Dae-Sung Kim; Dong-Jin Lee; Jin-Yeol Kim (pp. 814-818).
Polypyrrole-carbon nanotubes (CNTs) composite films, having high conductivity and uniformity, were directly synthesized by depositing polymerization in the gas-phase. The conductive polypyrrole was filled as a matrix material between the CNT networks by self-organization of the pyrrole monomer. Compared to the traditional composite technique and film-coating procedures, this process can be largely increased the carrier mobility for electrical conductivity because act to conducting bridge connecting PPy, increased the conductivity up to five times, and simultaneously improved the thermal stability. The characterization of the composite film was established by TEM, XRD, TGA, and IR/Raman spectroscopic analysis.
Keywords: Polypyrrole; Carbon nanotube; Composite; Gas-phase polymerization
Synthesis, characterization and nonlinear optical properties of 2-[( E)-2-(4-ethoxyphenyl)ethenyl]-1-methylquinolinium 4-substitutedbenzenesulfonate compounds
by Pumsak Ruanwas; Tawanrat Kobkeatthawin; Suchada Chantrapromma; Hoong-Kun Fun; Reji Philip; N. Smijesh; Mahesh Padaki; Arun M. Isloor (pp. 819-824).
In the present investigation, 2-[( E)-2-(4-ethoxyphenyl)ethenyl]-1-methylquinolinium 4-substituted benzenesulfonate (X=CH3 (1), X=OCH3 (2), X=Cl (3), X=Br (4)) have been synthesized and characterized by1H NMR, UV–Vis and FT-IR spectroscopy methods. In addition compound3 was also characterized by single crystal X-ray diffraction (XRD) and found that it crystallized out in the monoclinic space group P21 with cell parameters, a=9.8072(9)Å, b=6.4848(5)Å, c=19.4405(16)Å, α=90°, β=103.421(5)°, γ=90°, z=2 and V=1202.61(17)Å3. The nonlinear optical absorption of the samples has been studied at 532nm using 5ns laser pulses, employing the open-aperture z-scan technique. It is found that some of the samples are potential candidates for optical limiting applications.
Keywords: Nonlinear optics; Crystal structure; Quinolinium; Benzenesulfonate
Formation of hybrid spin crossover polymer microspheres
by Brandon Djukic; Marsha A. Singh; Martin T. Lemaire (pp. 825-828).
We report the formation of hybrid metallopolymer microspheres, deposited from an acetonitrile solution containing a known iron(3+) spin crossover complex bearing a thienyl substituent. We characterize the metallopolymer using SEM, FT-IR, elemental analysis (including C, H, N, S, Fe analyses), small-angle X-ray scattering (SAXS) techniques, and PXRD. Of greatest significance, the polymeric microspheres also exhibit spin crossover, conferring on metallopolymer2 the first spin crossover nanoscale material of its kind.
Keywords: Metallopolymers; Conjugated polymers; Hybrid materials; Spin crossover
White organic light-emitting devices with a bipolar transport layer between blue fluorescent and yellow phosphor-sensitized-fluorescent emitting layers
by Qin Xue; Guohua Xie; Ping Chen; Jianhua Lu; Dandan Zhang; Yanna Tang; Yi Zhao; Jingying Hou; Shiyong Liu (pp. 829-831).
We report white organic light-emitting devices (WOLEDs) based on 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) and phosphorescence sensitized 5,6,11,12-tetraphenylnaphthacene (rubrene). By introducing a bipolar transport 4,4′-N,N′-dicarbazole-biphenyl (CBP) layer between the fluorescent and the phosphor-sensitized-fluorescent layers, additional light emission from the phosphorescence sensitized layer is observed. This can be attributed to the elimination of the Dexter energy transfer between these two emitters. White emission with Commission International de L’Eclairage coordinates of (0.22,0.33) and a maximum luminance of 22,360cd/m2 were obtained. The maximum current efficiency can reach 10.7cd/A.
Keywords: White organic light-emitting diodes; Bipolar transport layer; Phosphorescence sensitized
Mechanical properties of polyaniline
by H. Valentová; J. Stejskal (pp. 832-834).
In spite of extensive electrical characterization of polyaniline, the information on its mechanical properties is missing in the literature. Complex Young's modulus of polyaniline compressed into pellets was measured at room temperature and an influence of preparation conditions of the polyaniline pellets on mechanical properties was studied. Young's modulus of PANI hydrochloride pellets was 0.9±0.2GPa and that of polyaniline base 1.3±0.2GPa. These values are comparable with common polymers, such as bulk polystyrene, 1.8±0.1GPa, or compressed polystyrene powder, 0.80±0.02GPa. Modulus of polyaniline is independent of the compression pressure above 300MPa, the time of compression had no effect.
Keywords: Polyaniline; Conducting polymer; Conductivity; Young's modulus; Mechanical properties; DMA
Color stable white polymer light-emitting diodes with single emission layer
by Sun Hee Kim; Youngeup Jin; Jin Young Yu; Jinwoo Kim; Suhee Song; Hongsuk Suh; Kwanghee Lee (pp. 835-838).
We report color stable white polymer light-emitting diodes achieved with single emission layers. The emitting layers are blending films of blue-, green- and red-emitting polymers based on color-stabilized backbones of poly(2,6-(4,4-bis(2-ethylhexyl)-4 H-cyclopenta[ def]phenanthrene)) (PCPP) and poly(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydroindeno[2,1- a]indene-2,7-diyl) (PININE). The white emission is realized with a combination of energy transfer and charge carrier trapping between the polymers in the devices. The devices exhibit a high color quality of white light with CIE coordinates of (0.31, 0.32) and excellent color stability as the driving voltage increases.
Keywords: PACS; 885.60.Jb; 78.60.FiPolymer light-emitting diodes; White emission