Synthetic Metals (v.156, #16-17)
Editorial Board (iii).
Synthesis, crystal structures and properties of new radical cation salts based on some tetrathiapentalene derivatives with halogenomercurate anions by E.I. Zhilyaeva; A.M. Flakina; R.N. Lyubovskaya; I.V. Fedyanin; K.A. Lyssenko; M.Yu. Antipin; R.B. Lyubovskii; E.I. Yudanova; J. Yamada (991-998).
New radical cation salts of BDH-TTP [2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene], BDA-TTP [2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] and DTDH-TTP [2-(1,3-dithiol-2-ylidene)-5-(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene] with halogenomercurate anions have been prepared. X-ray analysis at 120 K revealed the κ-type arrangement of conducting donor layers in (BDH-TTP)4Hg3Br8 and (BDH-TTP)4Hg3Cl8, and the β-type packing of donor layers in the (BDA-TTP)4Hg2Br6, (BDA-TTP)6Hg4I10.34 and (DTDH-TTP)6Hg3Br9 radical cation salts. The crystals of κ-(BDH-TTP)4Hg3Br8, κ-(BDH-TTP)4Hg3Cl8 and β-(DTDH-TTP)6Hg3Br9 behave as metals down to liquid helium temperatures, the resistivity of BDA-TTP salts shows semiconducting temperature dependence.
Keywords: Organic conductors based on radical cation salts; Electrical conductivity; X-ray diffraction;
The effects of acid treatment methods on the diameter dependent length separation of single walled carbon nanotubes by Youngjin Kim; Dockjin Lee; Youngseok Oh; Jaeboong Choi; Seunghyun Baik (999-1003).
The effects of acid treatment methods on the diameter dependent length separation of single walled carbon nanotubes were investigated using gel electrophoresis and Raman spectroscopic techniques. Carbon nanotubes were chemically treated using a mixture of H2SO4 and HNO3. The mechanism of gel electrophoresis is based on the migration of charged particles in an electric field, and the gel matrix acts as a sieve for the analyte. A comparative Raman spectroscopy analysis, performed on the migrated nanotubes in the gel, demonstrated that smaller diameter tubes were preferentially shortened by the acid treatments and moved farther during the gel electrophoresis.
Keywords: Single walled carbon nanotubes; Acid treatment methods; Raman spectroscopy; Length separation;
The use of cross-linkable interlayers to improve device performances in blue polymer light-emitting diodes by Seongyul Lee; Yi-Yeol Lyu; Soo-Hyoung Lee (1004-1009).
High efficiency blue PLEDs were fabricated by adding a thin interlayer between PEDT:PSS and emitting polymer layers. Two different cross-linkable alkoxysilane-based interlayer materials, X-NPB and X-PDA, were synthesized based on N,N′-bis(4-methylphenyl)-N,N′-diphenyl-1,4-phenylenediamine (PDA) and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1-biphenyl-4,4-diamine (NPB) which are well-known OLED HTLs. The devices, with configuration of indium tin oxide (ITO)/PEDT:PSS (65 nm)/interlayer (10–20 nm)/emitting polymer layer (70 nm)/BaF2 (2 nm)/Ca (50 nm)/Al (300 nm), were fabricated by spin coating and thermal evaporation. In this device structure, the cross-linked X-NPB or X-PDA interlayers are more adherent and mechanically robust as well as impervious to spin coating of next emitting polymer layer. In addition, the devices with these interlayers exhibit a higher luminescence and current efficiency than those without interlayers because interlayers have two functions which are blocking electrons and preventing from severe quenching by PEDT:PSS.
Keywords: Organic light-emitting diodes; Interlayer; Cross-link;
Crystal and molecular structure of the new anion-radical salts—(N-Me-2-NH2-Pz)(TCNQ)2 and (N-Me-Tetra-Me-Pz)(TCNQ)2 (Pz is pyrazine) by O.N. Kazheva; D.V. Ziolkovskiy; G.G. Alexandrov; A.N. Chekhlov; O.A. Dyachenko; V.A. Starodub; A.V. Khotkevich (1010-1016).
Two anion-radical salts (ARS) of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) – (N-Me-2-NH2-Pz)(TCNQ)2 and (N-Me-Tetra-Me-Pz)(TCNQ)2 (N-Me-2-NH2-Pz, N-methyl-2-amino-pyrazinium-; N-Me-Tetra-Me-Pz, N-methyl-tetra-methyl-pyrazinium-ions) – were synthesized and characterized. Both salts (ARS) were found to be semiconductors with a room-temperature conductivity of 3.8 × 10−5 and 1.93 × 10−2 Ω−1 cm−1, respectively. For both salts a layered structure of cations and anion-radicals was discovered, where layers composed of cations alternate along the b-axis with the layers containing TCNQ anion-radicals. The cations in the (N-Me-2-NH2-Pz)(TCNQ)2 form pairs bonded by strongly shortened 1.97 (2) Å intermolecular hydrogen N(1)…H(3a) links.
Keywords: 7,7′,8,8′-Tetracyanoquinodimethane; Pyrazine; Anion-radical salts; Organic conductors;
Fast trilayer polypyrrole bending actuators for high speed applications by Y. Wu; G. Alici; G.M. Spinks; G.G. Wallace (1017-1022).
The synthesis and performance evaluation of trilayer bending type polymer actuators in terms of frequency response and step response are described. The actuators are shown to achieve mechanical resonance at up to 90 Hz and giving tip displacements up to 60 mm for an input voltage of ±1 V at 4 Hz. Polypyrrole doped with trifluoromethanesulfonimide (TFSI) had a considerably higher speed of response when compared to polypyrrole-hexafluorophosphate (PF6) actuator with the same dimensions. The TFSI doped polypyrrole showed faster charging rates, likely due to higher ion diffusion rates through a gel-like polymer structure, thereby producing faster actuation response. These new actuators may be useful for applications requiring a high speed of response, e.g. a propulsion element for a swimming device/robotic fish.
Keywords: Polypyrrole; Actuator; Amplitude; Frequency; Speed;
Intercalation of polypyrrole into graphite oxide by Rabin Bissessur; Peter K.Y. Liu; Stephen F. Scully (1023-1027).
In this paper we report on the insertion of polypyrrole into layered graphite oxide. This was achieved by using the exfoliating and re-stacking properties of the host. The resulting intercalated product was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermogravimetric analysis and scanning electron microscopy.
Keywords: Intercalation chemistry; Graphite oxide; Polypyrrole;
Highly efficient organic light-emitting diodes using novel hole-transporting materials by Young Kook Kim; Seok-Hwan Hwang (1028-1035).
A new class of tetraminobiphenyl derivatives, which contains a 3,3′,5,5′-tetraminobiphenyl core, has been synthesized and examined as a hole-transporting material for organic light-emitting diodes. We fabricated the organic light-emitting diode (OLED) cells with tetraminobiphenyl derivatives as hole-injecting layer, hole-transporting layer and hole-injecting and transporting layer for green device with tris(8-quinolinolato)aluminum (Alq3) doped with 1% of Coumarin 545T (C545T) as green emitting layer. Tetraminobiphenyls were found to be useful as a novel hole-transporting material. The electroluminescent device with the 3,3′,5,5′-tetrakis(p-tolyldiamino)biphenyl (TTAB) as a hole-transporting layer was more efficient than that with the analogous triarylamine, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl benzidine (NPB). The external luminous efficiency of the device IV having TTAB as one hole-injecting and transporting layer can reach 14.55 cd/A, which is higher than the standard device I (11.66 cd/A) using two layers, a hole-injecting layer and a hole-transporting layer.
Keywords: Organic light-emitting diodes (OLEDs); Tetraminobiphenyl derivatives; Triarylamine; Hole-transporting material;
Poly(2,5-dimethoxy aniline)/fluoropolymer blend coatings to corrosion inhibition on stainless steel by Gastón Alvial Moraga; Glaura Goulart Silva; Tulio Matencio; Roberto Magalhães Paniago (1036-1042).
Heterogeneous blends of a soluble substituted polyaniline, poly(2,5-dimethoxy aniline) (PDMA), and two fluoropolymers, poly(vinylidene fluoride) and poly(tetrafluoroethylene-co-vinylidene fluoride-co-propylene) were prepared by casting. The use of this ternary system allowed the compatibilization of the polymer mixture and the improvement of the adhesion to the substrate of stainless steel. Three compositions with increase content of PDMA were investigated and compared with PDMA coating behavior. The superficial composition of the coatings was characterized by wide-scan X-ray photoelectron spectroscopy, which indicated that the steel surface is totally covered by the polymers. Chronopotentiometry at zero current systematic study was used to determine the open circuit potential (OCP). After 7 days immersion in saline solution, PDMA and the three blends showed similar OCP values of −170 mV (reduced state), which is shifted to more positive values in relation to the bare steel. Electrochemical impedance spectroscopy was used to characterize the polymeric coatings in the absence of active corrosion at the metal/coating interface. The blends showed higher R ct compared to PDMA (102–103 times) and this result was interpreted as a contribution of barrier of fluoropolymers. Salt spray test was used to evaluate the corrosive resistance of coatings and blends in aggressive conditions during 1000 h. Energy dispersive spectrometer semi-quantitative chemical analysis was performed on the coatings after the test and indicated that blends show superior resistance to the fog test in relation to the PDMA coating. Therefore, the blends PDMA/fluoropolymer behave as an electrochemical barrier as well as a physical barrier showing superior corrosion inhibition in relation to PDMA.
Keywords: Poly(2,5-dimethoxy aniline); Fluoropolymers; Blends; Impedance spectroscopy;
Spectral studies of new organic conductors: κ-(BDH-TTP)4Hg3X8, where X = Cl, Br by B. Barszcz; A. Łapiński; A. Graja; A. Flakina; E. Zhilyaeva; J. Yamada; R. Lyubovskaya (1043-1051).
Raman spectra of single crystals of κ-(BDH-TTP)4Hg3X8, where X = Cl, Br, were recorded in the 250–3000 cm−1 frequency range for two polarizations of incident light. Additionally, the polarized reflectance spectra of the single crystals of the compounds were recorded from 600 to 7000 cm−1 and fitted with the Lorentz model. The ab initio calculations of normal mode frequencies of the neutral BDH-TTP molecule, the BDH-TTP+ cation, and mercury-containing anions were performed. The calculations provided the assignment of vibrational modes observed in the experimental spectra. The analysis of the theoretical and the experimental Raman spectra suggests that both salts contain two kinds of donor molecules: differently charged or/and crystallographically independent ones.
Keywords: BDH-TTP salts; Organic conductor; IR spectroscopy; Raman spectroscopy; Ab initio calculation; X-ray data; dc conductivity;
Redox behavior and stability of polypyrrole film in sulfuric acid by Ying Tian; Fenglin Yang; Weishen Yang (1052-1056).
Acid concentration can profoundly affect the redox behavior and stability of polypyrrole film in sulfuric acid solution. The electrochemical characteristics during the redox process of polypyrrole films prepared with p-toluenesulfonate were investigated by cyclic voltammetry. The redox stability was studied by recurrent potential pulses experiments in different concentrations of sulfuric acid. The reduction charge value (Q red), the ratio of the reduction and oxidation charges (Q red/Q ox) were calculated from the experiments to exclude the polypyrrole films’ redox stability with the time and the reversibility of the reduction/oxidation process. FT-IR and SEM were used to study the structure and morphology change of ppy films treated by different concentrated sulfuric acid solutions, respectively.
Keywords: Polypyrrole film; Redox behavior; Redox stability; Sulfuric acid;
All-solid-supercapacitor based on polyaniline and sulfonated polymers by P. Sivaraman; S.K. Rath; V.R. Hande; A.P. Thakur; M. Patri; A.B. Samui (1057-1064).
All-solid-supercapacitor based on chemically synthesized polyaniline (PANI) and sulfonated polymers have been reported. Poly vinyl sulfonic acid (PVSA) is used as a proton conducting solid electrolyte. Fluorinated ethylene propylene copolymer grafted with acrylic acid and sulfonated (FEP-g-AA-SO3H) membrane was used as the separator. Composite electrodes were prepared from PANI, PVSA, electronically conducing carbon and poly tetra fluroethylene (PTFE) powder. Electrochemical studies of the supercapacitor were carried out in a unit cell. The unit cell consisted of three layers structure: composite electrode//FEP-g-AA-SO3H//composite electrode. This symmetric configuration of supercapacitor represents type1 (p-p) class, since both the electrodes were made from p-dopable PANI based composite electrodes. Optimization of solid electrolyte in the composite electrode was carried out. Supercapacitor was characterized by cyclic voltammetry and charge–discharge cycles. Capacitance of 98 F/g of PANI was obtained. The reduction in the capacitance after 1500 cycles was found to less than 20%. The non-ideal behavior of the supercapacitor was analyzed by impedance analysis.
Keywords: Polyaniline; Poly vinyl sulfonic acid; Sulfonated copolymer membrane; Supercapacitor;
The role of ionic conductivity and interface in electrical resistance, ion transport and transmembrane redox reactions through polyaniline membranes by N.M. Kocherginsky; Zheng Wang (1065-1072).
Three different physico-chemical properties of HCl-doped polyaniline (PANI) membranes, separating two aqueous solutions are compared. The first one is electrical conductivity measured with electrochemical impedance spectroscopy (EIS). The second one is H+ ion permeation through the membrane under pH gradient, measured with pH electrodes, and the third is electron/ion coupled counter transport in a transmembrane redox reaction, measured with redox electrodes. Electrophysical properties of undoped membrane are not described by the Ohm's law. The non-linear dependence is due to a limited content of mobile electrons and is similar to the Child's law known for vacuum diodes and dielectrics. Although the impedance of the doped membrane separating aqueous solutions is much less than that for the undoped membrane, it is determined by ions and not by electrons. For doped membranes the ratio of ion diffusion coefficient and charge drift mobility, determined in the external electrical field, is close to the Einstein relationship, meaning that the same ions play the key role in both processes. Thickness dependent behaviour is used to differentiate the interfacial properties from those of the bulk properties of the membrane. Interpolation of properties to zero membrane thickness shows that the interfacial charge transport plays an important role in doped membrane impedance and influences ion and redox transport rates. The relative role of interface versus volume increases with acid doping, which makes the bulk membrane volume more permeable for ions.
Keywords: Polyaniline; Membrane; Ionic conductivity; Interface;
Dual-type electrochromic devices based on both n- and p-dopable poly(dithieno[3,4-b,3′,4′-e]-[1,4]-dithiine) by Elif Sahin; Pinar Camurlu; Levent Toppare (1073-1077).
Polydithieno[3,4-b,3′4′-e]-[1,4]-dithiine (PDTH), being both n- and p-dopable, reveals remarkable color changes as both anodically and cathodically coloring material. In order to investigate its utilization in the electrochromic devices, three different transmissive/absorbtive type polymer electrochromic devices based on both p-type and n-type PDTH were assembled. These are, namely (1) p-type PDTH/poly(3,4-ethylenedioxythiophene) (PEDOT); (2) polythiophene/n-type PDTH; (3) p-type PDTH/n-type PDTH. Spectroelectrochemistry, switching ability, stability and open-circuit memory of the devices were investigated by UV–vis spectrophotometer and cyclic voltammetry. These devices exhibit reasonable switching times and stability under atmospheric conditions.
Keywords: Electrochromic devices; Electrochemical deposition; Anodically coloring material; Cathodically coloring material;
The preparation and gas sensitivity study of polypyrrole/zinc oxide by Lina Geng; Yingqiang Zhao; Xueliang Huang; Shurong Wang; Shoumin Zhang; Weiping Huang; Shihua Wu (1078-1082).
Polypyrrole (PPy) was prepared by chemical oxidation polymerization, analyzed by FT-IR, elemental analysis and HRTEM, and studied for gas sensitivity. It suggested that PPy had sensitivity to NH3, H2S and NO x , and showed irreversibility to NO x gas. The organic–inorganic hybrid materials PPy/ZnO with different PPy weight percents were prepared by mechanical mixing, and the sensitivity study of the materials to toxic gases NH3, H2S, NO x was carried out at different operating temperatures 30, 60, and 90 °C. It was found that PPy/ZnO materials (PPy(1%)/ZnO, PPy(3%)/ZnO, PPy(5%)/ZnO, PPy(10%)/ZnO, PPy(20%)/ZnO) had better selectivity and reversibility to NO x than pure PPy, and much lower working temperature than the reported working temperature of ZnO (about 350–450 °C). Their sensitivity increased with the increasing concentration of NO x at particular working temperature, and among them PPy(10%)/ZnO had the maximum sensitivity to NO x in the same condition. They showed no response to 1000, 1500, 2000 ppm NH3 or H2S. The response mechanism of PPy/ZnO materials to NO x was discussed.
Keywords: Preparation; Gas sensitivity; Polypyrrole; Zinc oxide;
Negative differential resistance and sample conductivity in polypyrrole films by V. Gomis; D. Bellver; N. Ferrer-Anglada; J.M. Ribó; Z. El-Hachemi; B. Movaghar (1083-1089).
An unusual negative differential resistance (NDR) has been observed in I–V response in p-toluensulfonate-doped polypyrrole films, leading to a conductivity switching effect of almost four orders of magnitude. The effect appears at temperatures below 20 K for highly conducting samples while it is displaced to temperatures close to the room temperature for more resistive samples. The observed correlation between conductivity and switching phenomenon provides a fingerprint of the influence played by the sample nanostructure. The relation between the chemical structure of the material and the observed physical phenomenon is discussed.
Keywords: Conducting polymer; Polypyrrole; Electrical conductivity; Metal–insulator phase transition;
Spirobifluorene derivatives for ultraviolet organic light-emitting diodes by Hideki Etori; Xiu Lan Jin; Takeshi Yasuda; Shuntaro Mataka; Tetsuo Tsutsui (1090-1096).
Four new spirobifluorene (SBF) derivatives, 1,3,5-tris(9,9′-spirobifluoren-2-yl)benzene (TSBFB), 1,3-bis(9,9′-spirobifluoren-2-yl)benzene (BSBFB), 2-(1-naphthyl)-9,9′-spirobifluorene (1SBFN), and 2-(2-naphthyl)-9,9′-spirobifluorene (2SBFN), were prepared as ultraviolet (UV)-emitting materials for organic light-emitting diodes (OLEDs). These SBF derivatives all have high glass transition temperatures (T g) above 95 °C, affording high-quality amorphous films with good morphological stability, and exhibit strong UV photoluminescence (PL) in solid state, showing no formation of excimers. In multilayer OLEDs using these SBF compounds as the emissive layers, the desired UV electroluminescence was achieved with high external quantum efficiencies of up to 2.9%. These results demonstrate that these compounds are promising UV-emitting materials for OLEDs.
Keywords: OLED; Ultraviolet emission; Spirobifluorene derivative;
Characteristics of the polyaniline films vacuum deposited at a high background pressure by Hui Li; Hong Qiu; Kun Fang; Jing Li; Chunying Fang (1097-1101).
Polyaniline films with different thickness were deposited on unheated glass substrates by vacuum evaporating HCl-doped polyaniline pellets at a high background pressure. Micromorphological, compositional, structural and electrical properties of the films were studied by using field emission scanning electron microscopy, energy dispersive of X-ray spectroscopy, Fourier transform infrared spectroscope and sub-femtoamp source meter. The polyaniline films consist of a large number of flakes. Some flakes are perpendicular to the substrate and they are more in the thick film compared with the thin film. No chlorine is detected in the films. The aromatic structure of polyaniline is retained in all the polyaniline films. However, the polar structure of polyaniline is destroyed in the films. The polyaniline film is in a higher oxidation state compared with the HCl-doped polyaniline pellet. The conductivity of the polyaniline films ranges from 10−8 to 10−9 S/cm and is lower than that of the HCl-doped polyaniline pellet as the starting material. Besides, the conductivity decreases with increasing film thickness.
Keywords: Polyaniline film; Vacuum deposited; High background pressure; Structure; Characteristic;
Transparent polymer cathode for organic photovoltaic devices by Abay Gadisa; Kristofer Tvingstedt; Shimelis Admassie; L. Lindell; X. Crispin; Mats R. Andersson; W.R. Salaneck; Olle Inganäs (1102-1107).
We demonstrate a prototype solar cell with a transparent polymer cathode, and indium-tin-oxide (ITO)/poly (3, 4-ethylene dioxythiophene)-poly (styrene sulphonate) (PEDOT:PSS) anode. As an active layer, thin film of a bulk heterojunction of polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2thienyl-2′,1′3′-benzothiadiazole)] (APFO-3) and an electron acceptor molecule -phenyl-C61-butyric acid methyl ester (PCBM) (1:4 wt.) was sandwiched between the two transparent polymer electrodes. The cathode is another form of PEDOT formed by vapor phase polymerised PEDOT (VPP PEDOT) of conductivity 102–103 S/cm. The cathode is supported on an elastomeric substrate, and forms a conformal contact to the APFO-3/PCBM blend. Transparent solar cells are useful for building multilayer and tandem solar cells.
Keywords: PEDOT; Vapor phase polymerization; VPP–PEDOT; Soft contact lamination; All-plastic solar cell; Ultraviolet photoelectron spectroscopy;
Inhomogeneous transport property of Alq3 thin films: Local order or phase separation? by I. Thurzo; H. Méndez; C. Iacoviţa; D.R.T. Zahn (1108-1117).
Steady-state current–voltage (I–V) and impedance–voltage (Z–V) measurements were performed on in situ (UHV) prepared metal (Ag, Al)/Alq3/indium-tin oxide (ITO) devices after exposure to air. When increasing the positive bias on the top metal electrode to a relatively well-defined critical value, a transition from semiconducting to semi- or even insulating behavior of the contacted Alq3 thin film is observed by means of I–V measurements. The final insulating state remains stable when applying negative bias to the Ag electrode. In the case of the Al electrode, there is a voltammetric current wave under a well-defined negative bias indicating a redox reaction of mobile ions at the Al electrode.The Z–V measurements reveal a peculiar feature of ac transport through the Alq3 thin films, namely the equivalent series capacitance is equal to its parallel counterpart in the frequency range from 100 to 1 MHz and amounts to only a fraction (0.3–0.5) of the expected geometrical capacitance of the device. An equivalent electrical circuit has been developed, based on the existence of two parallel transport paths: an insulating (amorphous) Alq3-phase shunted by a semiconducting (semi-insulating) one, both running into the impedance of the back contact. The equivalent circuit model composed exclusively of frequency independent elements is useful for predicting the maximum frequency for retaining the full geometrical capacitance. Even though the model is capable of describing the bias dependence of the impedance correctly, it does not shine light on the nature of the (ordered) phase or domain responsible for the dielectric loss. The possibility of local order connected with dipole–dipole interaction in the metal/Alq3 interface zone is discussed. In any case, the ordered portion of the organic material seems to form the huge interface dipole of about 1 eV with Ag or Al [M.A. Baldo, S.R. Forrest, Phys. Rev. B 64 (2001) 085201], the direction of the dipole promoting electron injection to Alq3. Then the semiconductor-to-insulator transition could be initiated by a damage of the interface dipole under a critical positive dc bias of the metal, preventing the flow of both dc and the real component of low-frequency ac current. The transition is not accompanied by any significant change in the impedance of the back contact common to both phases.
Keywords: Organic semiconductor; Conduction; Dielectric loss; Inhomogeneity;
Modification of soluble polyphenylene by Friedel–Crafts reactions: by Masahiro Abe; Takakazu Yamamoto (1118-1122).
Introduction of benzyl and toluoyl groups to a soluble p-phenylene/m-phenylene copolymer, PP, was carried out by Friedel–Crafts reactions using benzyl chloride and toluoyl chloride. Degrees of the introduction of the benzyl and toluoyl group per the phenylene unit of PP were estimated at 8.5 and 16.3%, respectively, from 1H NMR data. Original PP and the polymer with the benzyl group showed a strong photoluminescence with a quantum yield higher than 60% in chloroform. Introduction of the toluoyl group strongly affected the light emitting behavior of the polymer and caused a red shift of the emitted light.
Keywords: Conjugated polymers; Functionalization of polymers; Polyaromatics; Optical properties;
Synthesis, characterization, conductivity and thermal degradation of oligo-2-[(4-morpholin-4-yl-phenyl)imino]methylphenol and its oligomer–metal complex compounds by İsmet Kaya; Süleyman Çulhaoğlu; Murat Gül (1123-1132).
Schiff base oligomer of 2-[(4-morpholin-4-yl-phenyl)imino]methylphenol (2-MPIMP) was synthesized via oxidative polycondensation reaction by using air O2 and NaOCl oxidants in an alkaline medium between 40 and 90 °C. The structure of oligo-2-[(4-morpholin-4-yl-phenyl)imino]methylphenol (O-2-MPIMP) was characterized by using 1H, 13C NMR, FT-IR, UV–vis, size exclusion chromatography (SEC) and elemental analysis techniques. At the optimum reaction conditions, the yield of O-2-MPIMP was found to be 73% (for air O2 oxidant) and 97% (for NaOCl oxidant). According to the SEC measurements, the number-average molecular weight (M n), weight-average molecular weight (M w) and polydispersity index (PDI) values of O-2-MPIMP was found to be 1725, 2030 mol−1 and 1.177, respectively, using air O2 and 1345, 1490 g mol−1 and 1.108, using NaOCl, respectively. Oligomer–metal complex compounds were synthesized from the reactions of O-2-MPIMP with Cu2+, Co2+, Cd2+, Zn2+, Pb2+ and Zr4+ ions. Electrochemical the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and electrochemical energy gaps ( E ′ g ) for 2-MPIMP and O-2-MPIMP were found to be between −5.85 and −5.82, −2.63 and −2.87, 3.22 and 2.95 eV. Also, conductivity values of oligomer and oligomer–metal complex compounds were determined from their solid conductivity measurements. Conductivity measurements of doped and undoped Schiff base oligomer and its metal complexes were carried out by electrometer at room temperature and atmospheric pressure and were calculated from four-point probe technique. When iodine was used as doping agent, conductivity of this oligomer and its metal complexes were observed to be increased.
Keywords: Oligo-2-[(4-morpholin-4-yl-phenyl)imino]methylphenol; Thermal analyses; Oxidative polycondensation; Conductivity; Band gap;
Use of polymeric ionic liquids as stabilizers in the synthesis of polypyrrole organic dispersions by Rebeca Marcilla; Cristina Pozo-Gonzalo; Javier Rodríguez; Juan A. Alduncin; José A. Pomposo; David Mecerreyes (1133-1138).
Polypyrrole dispersions in several organic media were synthesized by using polymeric ionic liquids (PILs) both as steric stabilizers and as phase transfer agents. Firstly, PPy aqueous dispersions were prepared by polymerizing pyrrole in the presence of poly(1-vinyl-3-ethylimidazolium bromide) as steric stabilizer. By addition of different salts: lithium triflate, bis(trifluoromethane)sulfonimide lithium salt, bis(pentafluoroethane)sulfonimide lithium salt, dodecylbenzenesulfonic acid sodium salt and p-toluene-4-sulfonic acid monohydrate, the polymeric stabilizer becomes hydrophobic, precipitating in water and trapping the PPy dispersed microparticles inside. Polypyrrole organic dispersions were obtained by dispersion of the corresponding powders in a variety of organic solvents such as methanol, N,N-dimethylformamide (DMF), acetone, tetrahydrofurane (THF), butanone and toluene. The dispersability or non-dispersability of the PPy powders in each of the organic solvents depended on the nature of the added coagulating salt. Characterization of the PPy organic dispersions by photon correlation spectroscopy and atomic force microscopy (AFM) showed individual particles with sizes between 100 and 400 nm. After casting the organic dispersions, the films showed a granular nanostructured surface and electrical conductivity values as high as 10−1 S/cm.
Keywords: Conducting polymers; Polypyrrole dispersions; Polymeric ionic liquids; Phase transfer; Morphology; Nanostructured surface;
Synthesis, characterization and low frequency AC conduction of polyaniline/niobium pentoxide composites by Y.T. Ravikiran; M.T. Lagare; M. Sairam; N.N. Mallikarjuna; B. Sreedhar; S. Manohar; A.G. MacDiarmid; T.M. Aminabhavi (1139-1147).
New types of conducting polyaniline–niobium pentoxide (PANI/Nb2O5) nanocomposites have been synthesized by in situ deposition technique by placing fine grade powder of Nb2O5 during in situ polymerization of aniline. The composites formed were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). XRD and TEM indicated the dominant role-played by Nb2O5 particles, whereas XPS indicated incomplete protonation of imine moieties. SEM images indicated a systematic morphological variation of particles aggregated in the composite matrix as compared to the pristine PANI. Three step decomposition patterns were observed for PANI and its composites. AC conductivity and dielectric response of the composites were investigated in the frequency range, 102–106 Hz. AC conductivity obeyed the power law index, which decreased with increasing wt.% of Nb2O5. PANI showed high dielectric constant, which could be related to conductivity relaxation phenomenon. Both dielectric constant and dielectric loss decreased with increasing wt.% of Nb2O5. Variations in measured AC response parameters with increasing Nb2O5 contents of the composite followed systematic trends that are similar to those observed with decreasing temperature and level of doping.
Keywords: Polyaniline; Niobium pentoxide; Polymer composites; Electrical properties; Scanning electron microscopy; Thermogravimetric analysis;
Polyaniline by new miniemulsion polymerization and the effect of reducing agent on conductivity by Sambhu Bhadra; Nikhil K. Singha; Dipak Khastgir (1148-1154).
A new stable miniemulsion of aniline was prepared using sodium dodecyl sulphate (SDS) as the surfactant and cetyl alcohol as the cosurfactant. The oxidative polymerization reaction was initiated by ammonium peroxy disulphate (APS). At the end of the polymerization reaction polyaniline (PAni) formed was treated with stannous chloride (SnCl2) and finally doped with p-toluene sulphonic acid (PTSA). The monomer to oxidant and polymer to dopant mole ratio were optimized. Maximum conductivity is obtained with monomer to oxidant mole ratio1:1 and polymer to dopant mole ratio 1:0.5. There is a decrease in particle size and increase in the solubility in miniemulsion process. Dramatic increase in the conductivity is due to the treatment with SnCl2. Part of the pernigraniline (PNB) form of PAni formed was reduced by SnCl2 to emeraldine base (EB) form having higher conductivity. Plausible reduction mechanism with SnCl2 is proposed. The conduction mechanism is explained using EPR measurement. The reason for difference in conductivity of different forms of PAni is explained with the help of polaron formation and hole theory.
Keywords: Hopping mechanism; Miniemulsion polymerization; Polyaniline; Reduction;