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Percolation Threshold (percolation + threshold)
Kinds of Percolation Threshold Selected AbstractsHigh Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidene fluoride) and Exfoliated Graphite NanoplatesADVANCED MATERIALS, Issue 6 2009Fuan He A novel nanocomposite, based on poly-(vinylidene fluoride) and exfoliated graphite nanoplates (PVDF/xGnPs), exhibits high dielectric constant with a low percolation threshold, which can be attributed to the good dispersion of xGnP in the PVDF matrix and the formation of a large number of parallel-board microcapacitors. [source] Conductivity and Permittivity of Nickel-Nanoparticle-Containing Ceramic Materials in the Vicinity of Percolation ThresholdJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Umar Abdurakhmanov Conductivity and static permittivity of ceramic materials containing nanoparticles of Ni were measured in the vicinity of percolation threshold. It is found that, below this threshold, the experimentally obtained dependences of conductivity and static permittivity on the fractional Ni content in these materials are different from those calculated in the frame of the percolation theory. The origin of this discrepancy is discussed in terms of the network hierarchy model proposed recently by Balberg et al. for composite materials. [source] Glass Transition Temperature Depression at the Percolation Threshold in Carbon Nanotube,Epoxy Resin and Polypyrrole,Epoxy Resin CompositesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2005Sophie Barrau Abstract Summary: The glass transition temperatures of conducting composites, obtained by blending carbon nanotubes (CNTs) or polypyrrole (PPy) particles with epoxy resin, were investigated by using both differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). For both composites, dc and ac conductivity measurements revealed an electrical percolation threshold at which the glass transition temperature and mechanical modulus of the composites pass through a minimum. DC conductivity, ,dc, as a function of the conducting filler concentration of the CNT, (,) and PPy, (,) epoxy resin composites. [source] Time,Temperature,Transformation (TTT) Diagrams for Crystallization of Metal Oxide Thin FilmsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Jennifer L. M. Rupp Abstract Time,temperature,transformation (TTT) diagrams are proposed for the crystallization of amorphous metal oxide thin films and their specific characteristics are discussed in comparison to glass-based materials, such as glass-ceramics and metallic glasses. The films crystallize from amorphous to full crystallinity in the solid state. As an example the crystallization kinetics for a single-phase metal oxide, ceria, and its gadolinia solid solutions are reported made by the precipitation thin-film method spray pyrolysis. The crystallization of an amorphous metal oxide thin film generally follows the Lijschitz,Sletow,Wagner (LSW) Ostwald ripening theory: Below the percolation threshold of 20 vol% single grains crystallize in the amorphous phase and low crystallization rates are measured. In this state no impact of solute on crystallization is measurable. Once the grains form primary clusters above the threshold the solute slows down crystallization (and grain growth) thus shifting the TTT curves of the doped ceria films to longer times and higher temperatures in comparison to undoped ceria. Current views on crystallization of metal oxide thin films, the impact of solute dragging, and primary TTT diagrams are discussed. Finally, examples on how to use these TTT diagrams for better thermokinetic engineering of metal oxide thin films for MEMS are given, for example, for micro-Solid Oxide Fuel Cells and resistive sensors. In these examples the electrical properties depend on the degree of crystallinity and, thereby, on the TTT conditions. [source] Silver Surface Iodination for Enhancing the Conductivity of Conductive CompositesADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Cheng Yang Abstract The electrical conductivity of a silver microflake-filled conductive composites is dramatically improved after a filler surface treatment. By a simple iodine solution treatment, nonstoichiometric silver/silver iodide nanoislands form on the silver filler surface. Evidence of the decrease of surface silver oxide species is provided by TOF-SIMS and the redox property of the nanoclusters is studied using cyclic voltammetry and TOF-SIMS depth profile analyses. The redox property of the nanoclusters on silver flakes helps enhance the electrical conductivity of the conductive composites. The electrical resistivity of the improved conductive composites is measured by four-point probe method; the reliability of the printed thin film resistors is evaluated by both the 85 °C/85% relative humidity moisture exposure and the ,40 , 125 °C thermal cycling exposure. The conductive composite printed radio frequency identification (RFID) antennas with 27.5 wt% of the modified silver flake content show comparable performance in the RFID tag read range versus copper foil antennas, and better than those commercial conductive adhesives that require much higher silver content (i.e., 80 wt%). This work suggests that a surface chemistry method can significantly reduce the percolation threshold of the loading level of the silver flakes and improve the electrical conductivity of an important printed electronic passive component. [source] Silver Surface Iodination for Enhancing the Conductivity of Conductive CompositesADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Cheng Yang Abstract The electrical conductivity of a silver microflake-filled conductive composites is dramatically improved after a filler surface treatment. By a simple iodine solution treatment, nonstoichiometric silver/silver iodide nanoislands form on the silver filler surface. Evidence of the decrease of surface silver oxide species is provided by TOF-SIMS and the redox property of the nanoclusters is studied using cyclic voltammetry and TOF-SIMS depth profile analyses. The redox property of the nanoclusters on silver flakes helps enhance the electrical conductivity of the conductive composites. The electrical resistivity of the improved conductive composites is measured by four-point probe method; the reliability of the printed thin film resistors is evaluated by both the 85 °C/85% relative humidity moisture exposure and the ,40 , 125 °C thermal cycling exposure. The conductive composite printed radio frequency identification (RFID) antennas with 27.5 wt% of the modified silver flake content show comparable performance in the RFID tag read range versus copper foil antennas, and better than those commercial conductive adhesives that require much higher silver content (i.e., 80 wt%). This work suggests that a surface chemistry method can significantly reduce the percolation threshold of the loading level of the silver flakes and improve the electrical conductivity of an important printed electronic passive component. [source] Electrical Percolation Behavior in Silver Nanowire,Polystyrene Composites: Simulation and ExperimentADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Sadie I. White Abstract The design and preparation of isotropic silver nanowire-polystyrene composites is described, in which the nanowires have finite L/D (< 35) and narrow L/D distribution. These model composites allow the L/D dependence of the electrical percolation threshold, ,c, to be isolated for finite- L/D particles. Experimental ,c values decrease with increasing L/D, as predicted qualitatively by analytical percolation models. However, quantitative agreement between experimental data and both soft-core and core,shell analytical models is not achieved, because both models are strictly accurate only in the infinite- L/D limit. To address this analytical limitation, a soft-core simulation method to calculate ,c and network conductivity for cylinders with finite L/D are developed. Our simulated ,c results agree strongly with our experimental data, suggesting i) that the infinite-aspect-ratio assumption cannot safely be made for experimental networks of particles with L/D < 35 and ii) in predicting ,c, the soft-core model makes a less significant assumption than the infinite- L/D models do. The demonstrated capability of the simulations to predict ,c in the finite- L/D regime will allow researchers to optimize the electrical properties of polymer nanocomposites of finite- L/D particles. [source] Glass Fibers with Carbon Nanotube Networks as Multifunctional SensorsADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Shang-lin Gao Abstract A simple approach to deposit multiwalled carbon nanotube (MWNT) networks onto glass fiber surfaces achieving semiconductive MWNT,glass fibers is reported, along with application of fiber/polymer interphases as in-situ multifunctional sensors. This approach demonstrates for the first time that the techniques of conducting electrical resistance measurements could be applicable to glass fibers for in situ sensing of strain and damage; the techniques were previously limited to conductive and semiconductive materials. The electrical properties of the single MWNT,glass fiber and the "unidirectional" fiber/epoxy composite show linear or nonlinear stress/strain, temperature, and relative humidity dependencies, which are capable of detecting piezoresistive effects as well as the local glass transition temperature. The unidirectional composites containing MWNT,glass fibers exhibit ultrahigh anisotropic electrical properties and an ultralow electrical percolation threshold. Based on this approach, the glass fiber,the most widely used reinforcement in composites globally,along with the surface electrical conductivity of MWNTs will stimulate and realize a broad range of multifunctional applications. [source] Seismic singularities at upper-mantle phase transitions: a site percolation modelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Felix J. Herrmann SUMMARY Mineralogical phase transitions are usually invoked to account for the sharpness of globally observed upper-mantle seismic discontinuities. We propose a percolation-based model for the elastic properties of the phase mixture in the coexistence regions associated with these transitions. The major consequence of the model is that the elastic moduli (but not the density) display a singularity at the percolation threshold of the high-pressure phase. This model not only explains the sharp but continuous change in seismic velocities across the phase transition, but also predicts its abruptness and scale invariance, which are characterized by a non-integral scale exponent. Using the receiver-function approach and new, powerful signal-processing techniques, we quantitatively determine the singularity exponent from recordings of converted seismic waves at two Australian stations (CAN and WRAB). Using the estimated values, we construct velocity,depth profiles across the singularities and verify that the calculated converted waveforms match the observations under CAN. Finally, we point out a series of additional predictions that may provide new insights into the physics and fine structure of the upper-mantle transition zone. [source] Effective elastic properties of randomly fractured soils: 3D numerical experimentsGEOPHYSICAL PROSPECTING, Issue 3 2004Erik H. Saenger ABSTRACT This paper is concerned with numerical tests of several rock physical relationships. The focus is on effective velocities and scattering attenuation in 3D fractured media. We apply the so-called rotated staggered finite-difference grid (RSG) technique for numerical experiments. Using this modified grid, it is possible to simulate the propagation of elastic waves in a 3D medium containing cracks, pores or free surfaces without applying explicit boundary conditions and without averaging the elastic moduli. We simulate the propagation of plane waves through a set of randomly cracked 3D media. In these numerical experiments we vary the number and the distribution of cracks. The synthetic results are compared with several (most popular) theories predicting the effective elastic properties of fractured materials. We find that, for randomly distributed and randomly orientated non-intersecting thin penny-shaped dry cracks, the numerical simulations of P- and S-wave velocities are in good agreement with the predictions of the self-consistent approximation. We observe similar results for fluid-filled cracks. The standard Gassmann equation cannot be applied to our 3D fractured media, although we have very low porosity in our models. This is explained by the absence of a connected porosity. There is only a slight difference in effective velocities between the cases of intersecting and non-intersecting cracks. This can be clearly demonstrated up to a crack density that is close to the connectivity percolation threshold. For crack densities beyond this threshold, we observe that the differential effective-medium (DEM) theory gives the best fit with numerical results for intersecting cracks. Additionally, it is shown that the scattering attenuation coefficient (of the mean field) predicted by the classical Hudson approach is in excellent agreement with our numerical results. [source] High-Conductivity Polymer Nanocomposites Obtained by Tailoring the Characteristics of Carbon Nanotube Fillers,ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008Nadia Grossiord Abstract We present a detailed study of the influence of carbon nanotube (CNT) characteristics on the electrical conductivity of polystyrene nanocomposites produced using a latex-based approach. We processed both industrially-produced multi-wall CNT (MWCNT) powders and MWCNTs from vertically-aligned films made in-house, and demonstrate that while the raw CNTs are individualized and dispersed comparably within the polymer matrix, the electrical conductivity of the final nanocomposites differs significantly due to the intrinsic characteristics of the CNTs. Owing to their longer length after dispersion, the percolation threshold observed using MWCNTs from vertically-aligned films is five times lower than the value for industrially-produced MWCNT powders. Further, owing to the high structural quality of the CNTs from vertically-aligned films, the resulting composite films exhibit electrical conductivity of 103,S m,1 at 2,wt% CNTs. On the contrary, composites made using the industrially-produced CNTs exhibit conductivity of only tens of S m,1. To our knowledge, the measured electrical conductivity for CNT/PS composites using CNTs from vertically-aligned films is by far the highest value yet reported for CNT/PS nanocomposites at this loading. [source] Fabrication of radial ZnO nanowire clusters and radial ZnO/PVDF composites with enhanced dielectric properties,ADVANCED FUNCTIONAL MATERIALS, Issue 17 2008Guangsheng Wang Abstract Using an improved microemulsion process novel ZnO nanostructures can be prepared on a large scale. These radial ZnO nanowires grow on hexagonal prism tips and form nanowire clusters. A detailed study of variations in dielectric properties dependent on frequency and temperature shows that composites of radial ZnO and PVDF have significantly higher dielectric constants and exhibit better thermal stability than bulk ZnO/PVDF composites as well as showing a low percolation threshold. Already a low content of radial ZnO increases the dielectric constant of the polymer matrix significantly to a value above 100. [source] One-Step Ionic-Liquid-Assisted Electrochemical Synthesis of Ionic-Liquid-Functionalized Graphene Sheets Directly from Graphite,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2008Na Liu Abstract Graphite, inexpensive and available in large quantities, unfortunately does not readily exfoliate to yield individual graphene sheets. Here a mild, one-step electrochemical approach for the preparation of ionic-liquid-functionalized graphite sheets with the assistance of an ionic liquid and water is presented. These ionic-liquid-treated graphite sheets can be exfoliated into functionalized graphene nanosheets that can not only be individuated and homogeneously distributed into polar aprotic solvents, but also need not be further deoxidized. Different types of ionic liquids and different ratios of the ionic liquid to water can influence the properties of the graphene nanosheets. Graphene nanosheet/polystyrene composites synthesized by a liquid-phase blend route exhibit a percolation threshold of 0.1 vol % for room temperature electrical conductivity, and, at only 4.19 vol %, this composite has a conductivity of 13.84,S m,1, which is 3,15 times that of polystyrene composites filled with single-walled carbon nanotubes. [source] Three-dimensional Electrical Property Mapping with Nanometer ResolutionADVANCED MATERIALS, Issue 48 2009Alexander Alekseev The conductivity behavior of MWCNT networks within the volume of polymer nanocomposite samples is analyzed with nanometer resolution in all three dimensions. It is demonstrated that close to but above the percolation threshold for electrical conduction most of the MWCNTs do not contribute to the conductive network within the nanocomposite. [source] High Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidene fluoride) and Exfoliated Graphite NanoplatesADVANCED MATERIALS, Issue 6 2009Fuan He A novel nanocomposite, based on poly-(vinylidene fluoride) and exfoliated graphite nanoplates (PVDF/xGnPs), exhibits high dielectric constant with a low percolation threshold, which can be attributed to the good dispersion of xGnP in the PVDF matrix and the formation of a large number of parallel-board microcapacitors. [source] A Novel Percolative Ferromagnetic,Ferroelectric Composite with Significant Dielectric and Magnetic Properties,ADVANCED MATERIALS, Issue 3 2007Q. Huang A series of BaTiO3,Ni0.55Zn0.45Fe2.03O4composites are synthesized. The composites exhibit excellent dielectric and magnetic properties in the neighborhood of the percolation threshold,a high dielectric constant that is nearly temperature and frequency independent (see figure),and considerable initial permeability with excellent frequency stability, and may be useful as a high-performance multifunction ceramic composite. [source] Waterborne, Nanocomposite Pressure-Sensitive Adhesives with High Tack Energy, Optical Transparency, and Electrical Conductivity,ADVANCED MATERIALS, Issue 20 2006T. Wang Transparent and conductive pressure-sensitive adhesives are cast from aqueous colloidal dispersions of poly(butyl acrylate) (P(BuA)) and functionalized carbon nanotubes (CNTs). At the percolation threshold for network formation (at only 0.3,wt,% functionalized CNT), the nanotubes remarkably double the amount of strain at adhesive failure and increase the adhesion energy by 85,% (see figure). The tack properties are explained by current models of adhesive debonding. [source] Percolative Mechanism of Aging in Zirconia-Containing Ceramics for Medical Applications,ADVANCED MATERIALS, Issue 6 2003C. Pecharromán For biomedical applications, zirconia-toughened alumina ceramics (see Figure) would be very appropriate materials, provided that the zirconia content is kept below the percolation threshold (upper limit of 16 vol.-% 3Y-TZP inside an alumina matrix). That the concept of a percolation threshold is relevant when talking about aging degradation, is demonstrated by comparing specular IR reflectance measurements with aging experiments. [source] Prediction of the effective dielectric constant in SWNT polyimide nanocomposites using the Bruggemann modelJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Ricardo PérezArticle first published online: 27 APR 200 Abstract The Bruggemann model is used in this work to predict the effective dielectric constant of two kinds of single-wall carbon nanotube (SWNT) polyimide nanocomposites. Electrical conductivity and dielectric constant exhibit a dramatic enhancement at low content of SWNT fillers with a percolation threshold at 0.06 vol %. Results of the Bruggemann model are compared with the experimental values of the dielectric constant in CP2/SWNT and ,CN/SWNT polyimide nanocomposites. A reasonable agreement for SWNT contents under the percolation threshold and a SWNT dielectric constant of 2000 was found between the Bruggeman model modified by Giordano and the experimental values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Effects of the filler loading and aging time on the mechanical and electrical conductivity properties of carbon black filled natural rubberJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008A. R. Azura Abstract The effects of the filler loading and aging time on the mechanical and electrical conductivity properties of natural rubber were investigated. In this work, carbon black (type N220) was used as a filler, and its loading was varied from 0 to 50 phr. The mechanical properties (e.g., the tensile strength and catastrophic tearing energy) increased with a filler loading up to a certain loading, and a decrease in the mechanical properties was observed with higher filler loadings. The tensile strength and catastrophic tearing energy of the aged samples decreased after 3 and 6 days of aging at 100°C. The results for the electrical conductivity properties of unaged samples showed a percolation threshold at 20 phr, and the values were consistent with further filler loadings. After aging, the percolation threshold was still maintained at 20 phr. The morphologies of unaged and aged samples were significantly different: holes were observed to occur in the aged samples. This might have been due to the movement of fillers when the materials were subjected to heat, and this subsequently influenced the mechanical properties of the natural rubber composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Recycled carbon fiber filled polyethylene compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Tony McNally Abstract Composites of recycled carbon fiber (CF) with up to 30 wt % loading with polyethylene (PE) were prepared via melt compounding. The morphology of the composites and the degree of dispersion of the CF in the PE matrix was examined using scanning electron microscopy, and revealed the CF to be highly dispersed at all loadings and strong interfacial adhesion to exist between the CF and PE. Raman and FTIR spectroscopy were used to characterize the surface chemistry and potential bonding sites of recycled CF. Both the Young's modulus and ultimate tensile stress increased with increasing CF loading, but the percentage stress at break was unchanged up to 5 wt % loading, then decreased with further successive addition of CF. The effect of CF on the elastic modulus of PE was examined using the Halpin-Tsai and modified Cox models, the former giving a better fit with the values determined experimentally. The electrical conductivity of the PE matrix was enhanced by about 11 orders of magnitude on addition of recycled CF with a percolation threshold of 7 and 15 wt % for 500-,m and 3-mm thick samples. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Electrical behavior of polyurethane composites with acid treatment-induced damage to multiwalled carbon nanotubesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Pill Gyu Jang Abstract We have studied the electrical conductivity and percolation threshold of polyurethane (PU) composites filled with multiwalled carbon nanotubes (MWCNT) purified by increasing immersion time in aqueous solutions of either nitric acid or a mixture of nitric and sulfuric acids at 80°C. The MWCNT crystallinity peaks after 2 h of treatment, which enables the PU composites to enhance the percolation threshold and electrical conductivity in the conductive network formation region. MWCNT treated under either a milder or severer acidic condition deteriorate the electrical behavior of the composites, since MWCNT are poorly dispersed in the PU matrix in the former condition, but lost their intrinsic electrical conductivity due to the partial destruction of their crystalline structure in the latter. Therefore, the acid treatment needs to be carefully controlled to effectively purify the MWCNT, maintain the crystalline structure without further damage, and thereby improve the electrical behavior of PU/MWCNT composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Morphology and electrical properties of carbon black filled LLDPE/EMA compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Ping Zhou Abstract The morphology and electrical properties of linear low density polyethylene (LLDPE)/poly (ethylene-methyl arylate) (EMA) blends filled with carbon black (CB) are investigated in this work. Comparing to LLDPE/CB composite, the higher percolation threshold of EMA/CB composite is attributed to the good interaction between EMA and CB. However, carbon black is found to locate preferentially in the LLDPE phase of LLDPE/EMA immiscible blends from the characterization of SEM and electrical properties, which greatly decreases the percolation threshold of the composites. The viscosity of the two polymers is the key factor to determine the distribution of CB instead of interfacial energy in this system. This suggests a method to control the distribution of CB in the immiscible blends by choosing the viscosity ratio of polymer blend. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 487,492, 2007 [source] Schlieren formation in diatexite migmatite: examples from the St Malo migmatite terrane, FranceJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2003I. Milord Abstract Schlieren are trains of platy or blocky minerals, typically the ferromagnesian minerals and accessory phases, that occur in granites and melt-rich migmatites, such as diatexites. They have been considered as: (1) unmelted residue from xenoliths or the source region; (2) mineral accumulations formed during magma flow; (3) compositional layering; and (4) sites of melt loss. In order to help identify schlieren-forming processes in the diatexites at St Malo, differences in the size, shape, orientation, distribution and composition of the biotite from schlieren and from their hosts have been investigated. Small biotite grains are much less abundant in the schlieren than in their hosts. Schlieren biotite grains are generally larger, have greater aspect ratios and have, except in hosts with low (< 10%) biotite contents, a much stronger shape preferred orientation than host biotite. The compositional ranges of host and schlieren biotite are similar, but schlieren biotite defines tighter, sharper peaks on composition-frequency plots. Hosts show magmatic textures such as imbricated (tiled), unstrained plagioclase. Some schlieren show only magmatic textures (tiled biotite, no crystal-plastic strain features), but many have textures indicating submagmatic and subsolidus deformation (e.g. kinked grains) and these schlieren show the most extensive evidence for recrystallization. Magmas at St Malo initially contained a significant fraction of residual biotite and plagioclase crystals; smaller biotite grains were separated from the larger plagioclase crystals during magma flow. Since plagioclase was also the major, early crystallizing phase, the plagioclase-rich domains developed rapidly and reached the rigid percolation threshold first, forcing further magma flow to be concentrated into narrowing melt-rich zones where the biotite had accumulated, hence increasing shear strain and the degree of shape preferred orientation in these domains. Schlieren formed in these domains as a result of grain contacts and tiling in the grain inertia-regime. Final amalgamation of the biotite aggregates into schlieren involved volume loss as melt trapped between grains was expelled after the rigid percolation threshold was reached in the biotite-rich layers. [source] Water-resistant conducting hybrids from electrostatic interactionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2007Jing Luo Abstract Conductive hybrids were prepared in a water/ethanol solution via the sol,gel process from an inorganic sol containing carboxyl groups and water-borne conductive polyaniline (cPANI). The inorganic sol was prepared by the hydrolysis and condensation of methyltriethoxysilane with the condensed product of maleic anhydride and aminopropyltriethoxysilane as a catalyst, for which the carboxyl counterion along the cPANI backbone acted as an electrostatic-interaction moiety. The existence of this electrostatic interaction could improve the compatibility of the two components and contribute to the homogeneous dispersion of cPANI in the silica phase. The electrostatic-interaction hybrids displayed a conductivity percolation threshold as low as 1.1 wt % polyaniline in an emeraldine base, showing 2 orders of magnitude higher electrical conductivity than that without electrostatic interactions. The electrostatic-interaction hybrids also showed good water resistance; the electrical conductivity with a cPANI loading of 16 wt % underwent a slight change after 14 days of soaking in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1424,1431, 2007 [source] Raman spectroscopy of conducting poly (methyl methacrylate)/polyaniline dodecylbenzenesulfonate blendsJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2010Abdul Shakoor Abstract Polyaniline soluble in organic solvents was prepared using dodecylbenzenesulphonic acid (DBSA) as functional dopant. The solubility parameter was calculated and the most suitable solvent chloroform was checked for the solubility and the most compatible polymer PMMA was selected for blending. Miscibility was maximized with 1% by weight of hydroquinone. Blending of doped polyaniline with dodecylbenzenesulphonic acid (PAni.DBSA) in poly (methyl methacrylate) (PMMA) was explained by a change in the conformation of the polymeric chains leading to an increase in the conductivity. The electrical conductivity increased as the weight percent of PAni.DBSA increased, showing a percolation threshold as low as 3.0% by weight and the highest conductivity was achieved at 20% by wt of PAni.DBSA. Scanning electron micrographs showed lowest level of phase separation. Raman spectroscopy is used to characterize the blending process of two polymers aiming to understand the transformations in different types of charged segments. Raman results give complementary data about the blending process showing that together with the structural change of the polymeric chains, there is also a chemical transformation of these polymers. Analysis of Raman spectra was done investigating the relative intensities of the bands at 574 cm,1 and 607 cm,1. A relationship between conductivity and Raman was also proposed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of Multiwall Carbon Nanotubes on Electrical and Dielectric Properties of Yttria-Stabilized Zirconia CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006Sui-Lin Shi MWCNT/3Y-TZP (3 mol% yttria-stabilized tetragonal polycrystalline zirconia) composites with different multiwall carbon nanotube (MWCNT) contents were prepared by the spark plasma sintering technique. The effect of MWCNT addition on the electrical and dielectric properties of the composites at room temperature was studied. The experimental results showed that the DC conductivity of the composites demonstrated a typical percolation behavior with a very low percolation threshold between 1.0 and 2.0 wt% MWCNT content, and the dielectric constant was greatly increased when the MWCNT concentration was close to the percolation threshold, which was attributed to dielectric relaxation, the space charge polarization effect, and the percolation effect. [source] Conductivity and Permittivity of Nickel-Nanoparticle-Containing Ceramic Materials in the Vicinity of Percolation ThresholdJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Umar Abdurakhmanov Conductivity and static permittivity of ceramic materials containing nanoparticles of Ni were measured in the vicinity of percolation threshold. It is found that, below this threshold, the experimentally obtained dependences of conductivity and static permittivity on the fractional Ni content in these materials are different from those calculated in the frame of the percolation theory. The origin of this discrepancy is discussed in terms of the network hierarchy model proposed recently by Balberg et al. for composite materials. [source] Yodel: A Yield Stress Model for SuspensionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Robert J. Flatt A model for the yield stress of particulate suspensions is presented that incorporates microstructural parameters taking into account volume fraction of solids, particle size, particle size distribution, maximum packing, percolation threshold, and interparticle forces. The model relates the interparticle forces between particles of dissimilar size and the statistical distribution of particle pairs expected for measured or log-normal size distributions. The model is tested on published data of sub-micron ceramic suspensions and represents the measured data very well, over a wide range of volume fractions of solids. The model shows the variation of the yield stress of particulate suspensions to be inversely proportional to the particle diameter. Not all the parameters in the model could be directly evaluated; thus, two were used as adjustable variables: the maximum packing fraction and the minimum interparticle separation distance. The values for these two adjustable variables provided by the model are in good agreement with separate determinations of these parameters. This indicates that the model and the approximations used in its derivation capture the main parameters that influence the yield stress of particulate suspensions and should help us to better predict changes in the rheological properties of complex suspensions. The model predicts the variation of the yield stress of particulate suspensions to be inversely proportional to the particle diameter, but the experimental results do not show a clear dependence on diameter. This result is consistent with previous evaluations, which have shown significant variations in this dependence, and the reasons behind the yield stress dependence on particle size are discussed in the context of the radius of curvature of particles at contact. [source] Interpreting Impedance Response of Silicon Carbide Whisker/Alumina Composites Through Microstructural SimulationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006David S. Mebane A three-dimensional, object-defined Monte Carlo simulation is applied to alumina-silicon carbide whisker ceramic matrix composites. The simulation takes whisker orientation and size distributions into account simultaneously, and calculates a connectivity factor that relates whisker conductivity to macroscopic conductivity. Simulation results are compared with electrical measurements taken on real samples via impedance spectroscopy. Results show that the effect of whisker clumping can be seen in the impedance response as a decrease in the overall measured conductivity. Results also show that interfacial resistance influences the overall resistivity strongly relative to connectivity at volume fractions far above the percolation threshold. The possible mechanisms for interfacial resistance in the composite and their effect on the impedance response are discussed. [source] | |||||||||||||||||||||||||||||||