Conductive behavior and ionic conductivity of composite polymer electrolytes

The ac impedance plots of ( PEO)(16) LiClO4-EC composite polymer electrolytes were studied. The equivalent circuit of stainless steel electrode(SS)/composite electrolyte/SS system was applied to explain the ac impedance plots, The results showed that the equivalent circuit could fit the experimental data very well. The ionic conductivity was calculated using the bulk resistance that was obtained from equivalent circuit. The effect of EC on the conductive behavior was explained by the interactions among different species formed in the composite polymer electrolytes. For lower EC concentration samples, the temperature dependence of conductivity in low temperature range followed Arrhenius type, but when EC concentration was larger than 20%, the temperature dependence of conductivity obeyed the Vogel-Tamman-Fulcher (VTF) equation in all temperature ranges.

Preparation and properties of polyimide films codoped with barium and titanium oxides

Polyimide hybrid films containing bimetalic compounds were obtained by codoping poly(amic acid) with a barium and titanium precursor prepared from BaCO3, Ti(OBu)(4), and lactic acid followed by casting and thermal curing. FTIR, WAXD, and XPS measurements showed that barium and titanium precursor could be transformed to BaTiO3 at a temperature above 650 degreesC, while the mixed oxides were only found in hybrid films. The measurements of TEM and AFM indicated a homogeneous distribution of inorganic phase with particle sizes less than 50 nm. The hybrid films exhibited fairly high thermal stability, good optical transparency, and promising mechanical properties. The incorporation of 10 wt % barium and titanium oxide lowered surface and volume electrical resistivity by 2 and 5 orders, respectively, increasing dielectric constant from 3.5 to 4.2 and piezoelectric constant from 3.8 to 5.2 x 10(-12) c/N, relative to the nondoped polyimide film.

Polymer/silica nanoscale hybrids through sol-gel method involving emulsion polymers. 1. Morphology of poly(butyl methacrylate)/SiO2

In this article, we report on an approach of using an emulsion polymerized polymer in preparing organic-inorganic nanocomposites through a sol-gel technique. By mixing a polymer emulsion with prehydrolyzed tetraethoxysilane transparent poly(butyl methacrylate)/SiO2, nanocomposites were prepared as shown by TEM. AFM, FTIR, and XPS results show that there is a strong interaction between polymer latex particles and the SiO2 network. Comparison of the emulsion method with a traditional solution method shows that nanocomposites can be prepared by both methods, but there is some difference in their morphology and properties.

Nanocluster-containing mesoporous magnetoceramics from hyperbranched organometallic polymer precursors

Pyrolysis of hyperbranched poly[1,1'-ferrocenylene(methyl)silyne] (5) yields mesoporous, conductive, and magnetic ceramics (6). Sintering at high temperatures (1000-1200 degrees C) under nitrogen and argon converts 5 to 6N and 6A, respectively, in similar to 48-62% yields. The ceramization yields of 5 are higher than that (similar to 36%) of its linear counterpart poly[1,1'-ferrocenylene(dimethyl)silylene] (1), revealing that the hyperbranched polymer is superior to the linear one as a ceramic precursor. The ceramic products 6 are characterized by SEM, XPS, EDX, XRD, and SQUID. It is found that the ceramics are electrically conductive and possess a mesoporous architecture constructed of tortuously interconnected nanoclusters. The iron contents of 6 estimated by EDX are 36-43%, much higher than that (11%) of the ceramic 2 prepared from the linear precursor 1. The nanocrystals in 6N are mainly alpha-Fe2O3 whereas those in 6A are mainly Fe3Si. When magnetized by an external field at room temperature, 6A exhibits a high-saturation magnetization (M-s similar to 49 emu/g) and near-zero remanence and coercivity; that is, 6A is an excellent soft ferromagnetic material with an extremely low hysteresis loss.

Effect of physical aging on fracture behavior of polyphenylquinoxaline films

The influence of physical aging on the tensile fracture behavior of notched Polyphenylquinoxaline (PPQ-E) samples has been studied. The dependence of fracture stress and strain on physical aging has been explained. The glass transition temperature (T-g) and the endothermic peak at the end of T-g transition with different physical aging were characterized using differential scanning calorimetry (DSC) and the results have also been explained. The morphology of fracture surface was observed by scanning electron microscopy (SEM). (C) 2000 John Wiley & Sons, Inc.

Formation of conducting layers on excimer-laser-irradiated polyimide film surfaces

Conducting layers on KrF excimer-laser-irradiated polyimide film surfaces were investigated by XPS, SEM and Fourier transform infrared (FTIR)-Raman spectroscopy, Analysis of polyimide residue after laser irradiation provided valuable insight into the nature of the formation of conducting layers. The subtle different between KrF laser irradiation and the pyrolysis of polyimide was found by comparison of the formation process of conducting layers. A physical picture was presented to describe better the formation of conducting layers. Under KrF laser irradiation, polyimide films underwent thermal decomposition assisted by photoinduced direct bond breaking. Polycrystalline graphite was subsequently formed as the product of the secondary addition reaction of carbon-enriched clusters, Such reaction was supported by the remaining energy on the irradiated polyimide film surface. This result shows that the thermal process played an important role that was not just restricted to the formation of conducting layers, Copyright (C) 2000 John Wiley & Sons, Ltd.

Covalently attached multilayer assemblies containing photoreactive diazo-resins and conducting polyaniline

We reported on the multilayer architecture containing diazo-resins (DAR) as polycations and polyaniline poly(aniline-co-N-propanesulfonic acid aniline) (PAPSAH) as polyanions held together by electrostatic interaction. Upon UV irradiation, the adjacent interfaces of the multilayer reacted to form a covalently crosslinking structure which greatly improved the stability of the films as confirmed by solvent etching experiments. These changes were confirmed by UV-Vis and FTIR spectroscopy. The thickness of the covalently attached films were characterized with small angle X-ray diffraction (SAXD) and a value of 30.0 Angstrom per bilayer was obtained. This type of film was further characterized by cyclic voltammetry which showed that the electroactive property of PAPSAH was still kept in the films after photoreaction. (C) 2000 Elsevier Science B.V. All rights reserved.

Tuning the aggregation of polyimide thin films by modification of their molecular interactions

Thin films of an organo-soluble polyimide based on 1,4-(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA) have been studied. A prism coupler was used to measure the refractive indices. The average refractive indices of thin films prepared by annealing at different temperatures and times were chosen to characterize the condensation states of thin films. Thin films annealed at 200 degrees C show irreversible changes in physical properties, eg solubility. FTIR spectroscopy showed that the chain structures of the above thin films remained unchanged. It is proposed that specific molecular interactions induce the irreversible changes revealed by fluorescence spectroscopy. (C) 2000 Society of Chemical Industry.

Stimulated emission in the film of polymer/dye blend

Optically pumped stimulated emission behavior in an organic film was demonstrated in this study. The gain material consists of a laser dye perylene doped into polystyrene (PS) matrix in an appropriate weight ratio. The sample was transversely pumped by the three harmonic output of a mode-locked Nd:YAG laser. The change of the emission spectra showed a clear threshold action and gain narrowing phenomenon when increasing the excitation intensity. Three emission peaks were observed below the excitation threshold, which are locate at 446, 475 and 506 nm, respectively. However, only the gain narrowing peak centered at 475 nm could be detected above the threshold. The spectra narrowing observed results from the amplified spontaneous emission (ASE) in the gain material. (C) 2000 Elsevier Science S.A. All rights reserved.

Electrochemical behavior and electrocatalytic properties of ultrathin films containing silicotungstic heteropolyanion SiW12O404-

We describe here a controlled fabrication of ultrathin monolayer and multilayer films consisting of silicotungstic heteropolyanion SiW12O404- and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) on Au electrodes previously self-assembled with cysteamine monolayers based on layer-by-layer electrostatic interaction. The thus-forming monolayer and multilayer chemically modified electrodes are investigated by cyclic voltammetry on their electrochemical behavior and electrocatalytic properties. The composite ultrathin films exhibit remarkable electrocatalytic effects on the reduction of BrO3-, H2O2, and HNO2. The electrocatalytic effects on HNO2 reduction are enhanced with increasing layer number from 1 to 3 but level off with much thicker multilayers. The stability of the monolayer and multilayer films is also examined. (C) 2000 The Electrochemical Society. S0013-4651(99)04-057-4. All rights reserved.

Formation of mesophase mono-domains and micro-structures in thin films of a series of copolyethers containing both odd-numbered methylene units

The structural and morphological evolution of mono-domains in thin films has been investigated for a series of liquid crystalline (LC) copolyethers. The copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4 ' -biphenylyl)-2-(4-hydroxyl-phenyl)propane (TPP) with 1,7-dibromoheptane and 1,11-undecane at different compositions (coTPPs-7/11). In contrast to the solution-cast thin films without annealing, which exhibit the isotropic homogeneous molecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the high-temperature columnar phase (Phi '). Similar to the nucleation process in polymer crystallization, transmission electron microscopic observations show that small mono-domains appear in the initial stage of annealing, where molecules form a uniaxial in-plane chain orientation. With increasing annealing time, the molecular orientation gradually became tilted with respect to the substrate surface, and finally, a uniaxial homeotropic molecular orientation was achieved after a prolonged annealing time. The lateral size of mono-domains was found to increase continuously with annealing time and grew into a circular shape, indicating an isotropic lateral growth scheme which implies a hexagonal molecular packing proved by the electron diffraction experiments.

Electrostatic-field-induced chain alignment of liquid crystalline copolyether TPP thin films

A liquid crystalline (LC) copolyether has been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane with 1,7-dibromoheptane and 1,11-dibromoundecane with a 50/50 (both in %) equal composition of the 7- and 11-methylene monomers [coTPP-7/11(5/5)]. A mono-domain with a homeotropic alignment can be induced by a thin film surface in the LC phase. When an electrostatic field is applied to the surface-induced mono-domains parallel to the thin film surface normal, the molecular alignment undergoes a change from the homeotropic to uniaxial homogeneous arrangement. However, when the field is applied to a direction perpendicular to the thin film surface normal. the molecular alignment is about 10 degrees -tilt with respect to the homeotropic alignment toward the a*-axis. This is because the permanent dipole moment of the copolyether is not right vertical to the molecular direction. The calculation of molecular dipoles indicates that the permanent dipole moment of this copolyether is about 70 degrees away from the molecular axis, which leads to a negative dielectric anisotropy. It is speculated that the 10 degrees- rather than 20 degrees -tilt is due to a balance between the alignment induced by the electrostatic field and the surface. In the electrostatic field, molecules are subjected to a torque tau, which is determined by the permanent dipole moment P and the electrostatic field E: tau = P x E. The molecular realignment in both parallel and perpendicular directions to the thin film surface normal is determined by satisfying the condition of tau = P x E = 0. (C) 2001 Elsevier Science Ltd. All rights reserved.

Preparation of polyimide-BaTiO3 hybrid films by a dispersion process and their microstructure

Barium titanate (BaTiO3) powders with particle sizes of 30 similar to 50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wit % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.

Formation and characterization of heteropolyacid/polycation multilayer films on gold electrode

Ultrathin multilayer films of a polybasic lanthanide heteropoly tungstate-molybdate complex and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) have been fabricated on a gold electrode precoated with a cysteamine self-assembled monolayer. The multilayer films have been characterized by optical spectroscopy, small-angle X-ray diffraction, and electrochemical methods (cyclic voltammetry and electrochemical impedance). Especially, the electrochemical impedance spectroscopy is developed to monitor the layer deposition processes. It provides important information such as double-layer capacitance and charge-transfer resistance. All obtained results reveal regular film growth with each layer adsorption. (C) 2001 The Electrochemical Society.

Electrochemical growth and characterization of polyoxometalate-containing monolayers and multilayers on alkanethiol monolayers self-assembled on gold electrodes

A general strategy has been developed for fabrication of ultrathin monolayer and multilayer composite films composed of nearly all kinds of polyoxometalates (POMs), including isopolyanions (IPAs), and heteropolyanions (HPAs). It involves stepwise adsorption between the anionic POMs and a cationic polymer on alkanethiol (cysteamine and 3-mercaptopropionic acid) self-assembled monolayers (SAMs) based on electrostatic interaction. Here a Keggin-type HPA SiMo11VO405- was chosen as a main representative to elucidate, in detail, the fabrication and characterization of the as-prepared composite films. A novel electrochemical growth method we developed for film formation involves cyclic potential sweeps over a suitable potential range in modifier solutions. It was comparatively studied with a commonly used method of immersion growth, i.e., alternately dipping a substrate into modifier solutions. Growth processes and structural characteristics of the composite films are characterized in detail by cyclic voltammetry, UV-vis spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), micro-Fourier transform infrared reflection-absorption spectroscopy (FTIR-RA), and electrochemical quartz crystal microbalance (EQCM). The electrochemical growth is proven to be more advantageous than the immersion growth. The composite films exhibit well-defined surface waves characteristic of the HPAs' redox reactions. In addition, the composite films by the electrochemical growth show a uniform structure and an excellent stability. Ion motions accompanying the redox processes of SiMo11VO405- in multilayer films are examined by in situ time-resolved EQCM and some results are first reported. The strategy used here has been successfully popularized to IPAs as well as other HPAs no matter what structure and composition they have.