Structure and electrical properties of undoped oriented poly(phenylene vinylene) films

The influence of anisotropic structure on the electrical properties of undoped oriented poly(phenylene vinylene) (PPV) films was investigated with impedance spectroscopy and structural characterization. The oriented structure of the stretched PPV films was studied with wave-guide coupling and infrared dichroism. It was found that the unstretched PPV film had a highly planar structure, and one-way stretching converted the planar structure into a uniaxial structure. The impedance of undoped PPV thin films was measured along three different directions: through the film thickness direction, parallel to the stretch direction in the film plane, and perpendicular to the stretch direction in the film plane. Two relaxations were observed, one corresponding to the bulk behavior in the high-frequency range and the other to an interfacial contact polarization in the low-frequency range. From equivalent circuit modeling, it was found that the bulk conductivity through the film thickness direction decreased with increasing orientation, whereas the high-frequency dielectric constant through the film direction remained constant. In addition, the conductivities measured in the film plane were at least two orders of magnitude higher than the conductivity in the direction normal to the film surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 98–116, 2004     

Structural and electrical characterisation of betaine-type,organic, molecular,thin evaporated films and LB multilayers

The structure and electrical properties of highly polar indandione-1,3 pyridinium betaine (IPB) derivatives have been studied in vacuum-evaporated thin films and Langmuir-Blodgett (LB) multilayer assemblies. Phase transitions induced by temperature and/or electric field have been observed in LB films of an amphiphilic derivative of IPB.The LB films of IPB, obtained at room temperature, form a Y-like structure which melts at about 50 °C to produce spherical domains, having Z-like structure, which remain stable up to 110 °C. Similar phase transitions can be induced by an electric field with ε ≥ 2 × 10⁵ V cm⁻¹ at room temperature. In the new Z-like phase of the IPB LB films, the electrical conductivity increases by some five or six orders of magnitude and the activation energy of dark conductivity decreases from 0.18 ± 0.03 eV to practically zero.The vacuum-evaporated IPB films yield low electrical conductivity (σ = 10⁻¹⁵–10⁻¹⁶S cm⁻¹), whereas in the LB multilayers a notable anisotropy of conductivity is observed. In case of coplanar cells the conductivity increases to σ = 10⁻⁸S cm⁻¹. In sandwich-type LB samples the conductivity value is similar to that of the vacuum-evaporated polycrystalline thin films.     

Crystallographically oriented mesoporous WO3 films: synthesis, characterization, and applications.

Mesoporous semiconducting films consisting of preferentially orientated monoclinic-phase nanocrystals of tungsten trioxide have been prepared using a novel version of the sol-gel method. Transformations undergone by a colloidal solution of tungstic acid, stabilized by an organic additive such as poly(ethylene glycol) (PEG) 300, as a function of the annealing temperature have been followed by means of a confocal Raman microscope. The shape and size of WO3 nanoparticles, the porosity, and the properties of the films depend critically on preparation parameters, such as the tungstic acid/PEG ratio, the PEG chain length, and the annealing conditions. Well-crystallized WO3 films combine excellent photoresponse to the blue region of the solar spectrum, up to 500 nm, with good transparency at wavelengths larger than 550 nm. Particular applications of these nanocrystalline WO3 films include photoelectrochemical and electrochromic devices.     

The influence of structure change on electrical properties of conducting LB films produced from hexadecyl-TCNQ and heptadecyldimethyl-TTF mixture

Conducting Langmuir-Blodgett films of hexadecyl-TCNQ and heptadecyl dimethyl-TTF mixture in the ratios from 1:1 to 1:2.5 are studied. Temperature dependence of film conductivity possesses some specific features. Strong increase of conductivity and decrease of activation energy take place after annealing at 307–315 K. On the other hand, the film loses conductance after heating above 315 K. To explain this behaviour the investigations of conducting multilayers by means of electron diffraction, electron microscopy, and X-ray small-angle scattering were carried out. Some relations between changes of electrical properties and structural transformations are ascertained.     

Piezoelectric properties of oriented deoxyribonucleate films

The piezoelectric effect due to shear in oriented films of DNA is strongly dependent on the relative humidity at which the films are equilibrated. Below about 60% relative humidity, the sign of the piezoelectric modulus is negative and its magnitude passes through a maximum with increasing temperature. This type of polarization appears to be due to the stress-induced orientation of dipoles in sugar-phosphate main chain. Above 75% relative humidity, water molecules are adsorbed by the bases and stabilize the ordered structure of double strand helices. In this crystalline state, the sign of the piezoelectric modulus is positive and its magnitude decreases markedly at about?75°C. This type of polarization appears to be due to the stress-induced orientation of dipoles in bases attached to the main chain. From comparisons between piezoelectric, elastic, and dielectric measurements, it is concluded that the piezoelectric relaxation observed at?75°C and 75% relative humidity is mainly due to the dielectric relaxation of the bases in the double helix.     

两亲性卟啉-紫精化合物LB膜的结构及光电性质研究

本文制备了两亲性卟啉-紫精化合物的LB膜材料, 用π-A等温曲线、吸收光谱、小角和低角X射线衍射以及扫描隧道电镜(STM)等方法研究了LB膜的结构。结果表明, LB膜内分子排列是二维有序的超晶格结构, 卟啉环在基片上的排列呈"站立"状态。单个分子占有面积为1.15nm^2, 单层高度为2.35nm, 相邻裂间的距离为1.07nm。这种规则有序的两亲性卟啉-紫精化合物呈现出良好的光量子收率和光电响应特性。     

The electrical properties of heterogeneous mixtures containing an oriented spheroidal dispersed phase

Theoretical equations for the permittivity and conductivity of a heterogeneous mixture containing an oriented dispersed phase of spheroidal shape are limited to low volume fractions of dispersed phase. Two new sets of equations have been derived here for such systems using approaches which have been shown previously to be applicable to higher concentrations. One set has generalised forms of equations given by Bruggeman and Hanai and includes simplifications applicable to oil in water (O/W) and water in oil (W/O) systems. The other set has generalised forms of an equation given by Looyenga. Tabulated mixture permittivityε and dielectric incrementΔε values are presented and, with the exception ofO 〈W systems containing prolate spheroids, the two types of equation show significant differences in bothε andΔε. For both typesΔε is strongly dependent on the ratio of the conductivities of the two media of aW/O system. The relevance of the mixture equations to the electrical behaviour of micellar, microemulsion and liquid crystalline systems is considered.     

Lipophilic derivative of rhodamine 19: characterization and spectroscopic properties

A new octadecylamide derivative of rhodamine 19 was synthesized by reaction of rhodamine 19 ethyl ester (rhodamine 6 G) with octadecylamine. This lipophilic dye exists in two forms: as a cationic species containing a secondary amide group and as an electrically neutral molecule containing an additional ring closed between the oxygen of the amide group and the central carbon of the xanthene part. Both forms were isolated and characterized in detail by means of elemental analysis, mass spectrometry, IR, NMR and UV-VIS spectroscopy. Depending on the hydrogen ion activity in solution and the availability of solvent hydrogen for hydrogen bond formation, the cationic form easily converted into a neutral one and vice versa. On the basis of absorption and emission UV-VIS spectroscopic data, the equilibrium of the two forms was studied in various solvents. An increase in dye concentration in acidified methanol/water mixture (volume fraction of water, ?=80%) led to aggregation of the cationic molecules. Using the UV-VIS absorption data, a corresponding dimerization constant was evaluated.     

Synthesis, characterization, and sorption properties of silica gel-immobilized pyrimidine derivative

5-Benzylidene-2-thiobarbituric acid (BzTBA), a pyrimidine derivative, was used to modify the surface of silica gel-chloropropyltrimethoxysilane (Si-Cl) via chemical immobilization to produce a new pyrimidine silica phase (Si-BzTBA). Identification of the surface modification was characterized and performed on the basis of infrared as well as elemental analysis. Thermal desorption method was found to give 0.129-0.143 mmol g(-1) as surface coverage values. Metal sorption properties of Si-BzTBA were also studied and the evaluated results refer to the high metal sorption of Si-BzTBA for copper(II), mercury(II), cadmium(II), and lead(II) with the same order. These four Si-BzTBA-metal complexes were also synthesized and the stoichiometric ratios were identified as 1:1 except lead complex was found to give a 1:2 ratio. Electron impact-mass spectrometric analysis (EI-MS) with 70 eV ionization energy was used as a potential thermal method for the confirmation of surface modification of Si-BzTBA and its metal complexes based on fragmentation elucidation of thermally desorbed ion peaks. The EI-MS of Si-BzTBA was found to show several characteristic fragment ion peaks that are directly related to the chemical binding of BzTBA to SiCl phase. Differential scanning calorimetry study (DSC) was also performed to evaluate the various kinetic and thermodynamic parameters of thermal degradation processes and have been enumerated. The results of EI-MS and DSC are very similar in many respects.     

二茂铁衍生物LB膜修饰Pt电极的循环伏安法性能

本文研究了单取代二茂铁酯和双取代亚麻酸二茂铁酯LB膜修饰Pt电极的循环伏安法性能,用修饰电极的循环伏安模型对实验结果进行拟合,计算了在转移压力分别为20,30,40mN·m^-^1下LB膜修饰Pt电极的覆盖度,并分析和讨论了不同转移压力下修饰的二茂铁LB膜的电荷转移中介作用     

Single-walled carbon nanotube-based coaxial nanowires: synthesis, characterization, and electrical properties

We report herein the template-directed synthesis, characterization, and electric properties of single-walled carbon nanotube- (SWNT-) based coaxial nanowires, that is, core (SWNT)-shell (conducting polypyrrole and polyaniline) nanowires. The SWNTs were first dispersed in aqueous solutions containing cationic surfactant cetyltrimethylammonium bromide (CTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonyl phenyl ether (O pi-10). Each individual nanotube (or small bundle) was then encased in its own micellelike envelope with hydrophobic surfactant groups orientated toward the nanotube and hydrophilic groups orientated toward the solution. And thus a hydrophobic region within the micelle/SWNT (called a micelle/SWNT hybrid template) was formed. Insertion and growth of pyrrole or aniline monomers in this hybrid template, upon removal of the surfactant, produce coaxial structures with a SWNT center and conducting polypyrrole or polyaniline coating. Raman and Fourier transform infrared (FTIR) spectroscopy and scanning (SEM) and transmission (TEM) electron microscopy were used to characterize the composition and the structures of these coaxial nanowires. The results revealed that the micellar molecules used could affect the surface morphologies of the resulting coaxial nanowires but not the molecular structures of the corresponding conducting polymers. Electric properties testing indicated that the SWNTs played the key roles in the conducting polymer/SWNT composites during electron transfer in the temperature range 77 K to room temperature. Compared with the SWNT network embedded in the conducting polymers, the composites within which SWNTs were coated perfectly by the identical conducting polymers exhibited higher barrier heights during electron transfer.     

Synthesis,characterization, optical,thermal and electrical properties of polybenzimidazoles

The variation of dielectric constant and dielectric loss of two novel polybenzimidazole (PBI) were studied at constant temperature with variable frequency. The polymers have shown maximum dielectric constant at low applied frequency 50 Hz at 393 K due to the space charge polarization. The AC conductivity and activation energy of polymers were arrived from dielectric constant and dielectric loss values. PBIs were synthesized by the oxidative polycondensation of benzimidazole monomers, 2-(1H-benzo [d] imidazole-2-yl)-4-bromophenol (BIBP), and 2-(1H-benzo [d] imidazole-2-yl)-6-methoxyphenol (BIMP) in an aqueous alkaline medium using NaOCl as oxidant. The monomers and polymers were characterized by various spectroscopic techniques. Fluorescence spectra of monomers and polymers showed their λ _max emission in the region of 472–479 and 463–472 nm respectively. The electrical conductivities of iodine doped polybenzimidazoles were measured by four-point probe technique and it increases with increase in iodine vapour contact time. The electrical conductivity values were correlated with the charge density on imidazole nitrogen obtained from Huckel calculation method. Both the PBI are having reasonably good thermal stability and are shown by high carbines residues of around 40% at 500°C in thermogravimetric analysis.     

Structural,thermal, and electrical properties of carbonaceous films containing palladium nanocrystals

Carbonaceous films containing Pd nanocrystals can be applied as active layers in gas sensor applications. In this article we show results of studies of C-Pd films, obtained with two different methods: (1) physical and (2) physical + chemical deposition. First type of film prepared by physical vapor deposition (PVD) process was composed of fullerenes, amorphous carbon, and palladium nanograins. In the second method PVD film was modified in chemical vapor deposition (CVD) process forming a foam-like structure. Both types of films were studied by SEM, TEM, TGA, and electrical characterization (measurement of resistivity versus composition of gaseous hydrocarbons mixture).     

Synthesis, characterization, and sorption properties of silica gel-immobilized Schiff base derivative

Silica gel was derivatized with benzophenone 4-aminobenzoylhydrazone (BAH), a Schiff base derivative, after silanization of silica by 3-chloropropyltrimethoxysilane (CPTS) by using a reported method. Characterization of the surface modification was confirmed through infrared spectroscopy, thermogravimetry, and elemental analysis. The immobilized surface was used for Cu(II), Ni(II), Zn(II), and Co(II) sorption from aqueous solutions. The influence of the amount of sorbent, ion concentration, pH, and temperature was investigated. The sorption data followed Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. The mean sorption energy (E) of benzophenone 4-aminobenzoylhydrazone (BAH) immobilization onto silica gel was calculated from D-R isotherms, indicating a chemical sorption mode for four cations. Thermodynamic parameters, i.e., DeltaG, DeltaS, and DeltaH, were also calculated for the system. From these parameters, DeltaH values were found to be endothermic: 27.0, 22.7, 32.6, and 34.6 kJ mol(-1) for Cu(II), Ni(II), Co(II), and Zn(II) metal ions, respectively. DeltaS values were calculated to be positive for the sorption of the same sequence of divalent cations onto sorbent. Negative DeltaG values indicated that the sorption process for these three metal ions onto immobilized silica gel is spontaneous.     

Gold nanoparticles: assembly and electrical properties in 1-3 dimensions

Ligand stabilized gold nanoparticles have attracted much attention in the search for new chemically designed compounds for a future information technology, based on single-electron devices. This article gives an overview about the strategies used to synthesize and to assemble uniform gold nanoparticles in different dimensions as well as about the present status of the electrical properties of these. Examples are given for three-dimensional organisations, for the formation of self-assembled monolayers as well as for one-dimensional assemblies.     

Synthesis,characterization and enhanced electrical properties of CTAB-directed polyaniline nanoparticles

Inverse microemulsion system of cetyltrimethylammonium bromide (CTAB) molecules is utilized for virtually monodispersed and controlled growth of HCl polyaniline (PANI) nanoparticles at room temperature (ca. 300 K). The templated electroconductive polymer reveals lamellar crystalline structure under X-ray diffraction signifying marked sub-chain alignment of the polymerized nanoparticles. The nanostructured polymer has spherically symmetric morphology in a size range of 2.0 nm to 6.0 nm under electron microscope examination. Gel permeation chromatography gives polydispersity index of 1.02 for nanostructured polymer in agreement with the size monodispersity transpired by electron microscopy. The d.c. electrical conductivity σ _dc of PANI at room temperature is 10.11 S/cm whereas the variation of conductivity with temperature in the range 227–303 K reveals that the conducting mechanism can be considered as three-dimensional variable-range-hopping (3D-VRH). UV-Vis spectrum indicates two broad absorption bands due to polaron formation that contributes to enhanced electrical conductivity of the polymer. The fundamental absorption edge in the polymer is formed by direct allowed transitions to the extent that the optical band gap value was found to be 2.35 eV. The crystalline nanostructure and homogeneous doping attained in the cationic template of amphiphile are argued as contributing factors to the enhanced conductivity of the polymer.     

Ancillary ligand-controlled assembly of three coordination polymers: synthesis,characterization, luminescent,and catalytic properties

Abstract

By changing the ancillary ligands, three new zinc-based coordination polymers (CPs), {[Zn(4,4′-bpy)(H₂O)₄]·(TDC)·(H₂O)}_n (1), [Zn(2,2′-dmbpy)(TDC)]_n (2), and [Zn₂(3,3′-dmbpy)(TDC)₂]_n (3) (H₂TDC =2,5-thiophenedicarboxylic acid, 4,4′-bpy =4,4′-bipyridine, 2,2′-dmbpy =2,2′-dimethyl-4,4′-bipyridine, 3,3′-dmbpy =3,3′-dimethyl-4,4′-bipyridine) have been synthesized under the same reaction conditions (H₂O, pH =7–8, and 140°C) and were structurally characterized. 1 is a linear chain structure and further connected into a 3-D structure through hydrogen bonds. 2 shows a 2-D (4,4) network when the dinuclear [Zn₂(COO)₄N₂] building unit is regarded as a six-connected node. 3 has a twofold-interpenetrating 3-D zinc-organic framework pcu topology. Furthermore, 1–3 show strong photoluminescence at room temperature in the solid state, and the catalytic activities of 1–3 for degradation of methyl orange in a Fenton-like process have been investigated. The results suggest that the ancillary ligands influence the final resulting CPs.     

Structural characterization of a spin-assisted colloid-polyelectrolyte assembly: stratified multilayer thin films

The assembly of polyelectrolytes and gold nanoparticles yields stratified multilayers with very low roughness and high structural perfection. The films are prepared by spin-assisted layer-by-layer self-assembly (LbL) and are characterized by X-ray reflectivity (XRR), UV-vis spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Typical structures have four repeat units, each of which consists of eight double layers (DL) of poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride), one monolayer of gold nanoparticles (10 nm diameter), and another layer of poly(allylamine hydrochloride). XRR scans show small-angle Bragg peaks up to seventh order, evidencing the highly stratified structure. Pronounced Kiessig fringes indicate a low global roughness, which is confirmed by local AFM measurements. TEM images corroborate the layered structure in the growth direction and nicely show the distinct separation of the individual particle layers. An AFM study reveals the lateral gold particle distribution within one individual particle layer. Interestingly, the spin-assisted deposition of polyelectrolytes reduces the roughness induced by the particle layers, leading to self-healing of roughness defects and a rather perfect stratification.     

Synthesis, characterization, and electrical and electrochemical properties of sandwich dilutetium tetraphthalocyanine

Lu2Pc2 and lithium hexylthio-phthalocyanine have been used to synthesize [Lu2(Pc)4] which exhibits variable range hopping conductivity as inorganic semiconductors and also observed electrochromic effect from cyclic voltammetric (CV) measurement.