			Home About us Contact

Low Percolation Threshold (low + percolation_threshold)

Distribution by Scientific Domains

Polymers and Materials Science	81%

Distribution within Polymers and Materials Science

General & Introductory Materials Science	33%

Selected Abstracts

High Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidene fluoride) and Exfoliated Graphite Nanoplates

ADVANCED MATERIALS, Issue 6 2009
Fuan 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]

Fabrication of radial ZnO nanowire clusters and radial ZnO/PVDF composites with enhanced dielectric properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2008
Guangsheng 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]

High Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidene fluoride) and Exfoliated Graphite Nanoplates

Effect of Multiwall Carbon Nanotubes on Electrical and Dielectric Properties of Yttria-Stabilized Zirconia Ceramic

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006
Sui-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]

A Novel Concept for Highly Oriented Carbon Nanotube Composite Tapes or Fibres with High Strength and Electrical Conductivity

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2009
Hua Deng
Abstract A new concept is described for the creation of multifunctional polymer nanocomposite tapes (or fibres) that combines high stiffness and strength with good electrical properties and a low percolation threshold of carbon nanotubes (CNTs). The concept is based on a bicomponent tape (or fibre) construction consisting of a highly oriented polymer core and a conductive polymer composite (CPC) skin based on a polymer with a lower melting temperature than the core, enabling thermal annealing of these skins to improve conductivity through a dynamic percolation process while retaining the properties of the core and hence those of the tape (or fibre). The percolation threshold in the CPC skins of the highly drawn conductive bicomponent tapes could be decreased from 5.3 to 1.1,wt.-% after annealing. [source]

Electrically Conductive Poly(DL -lactide)/Chitosan/Polypyrrole Complexes

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2006
Ying Wan
Abstract Summary: The fabrication of novel conductive poly(DL -lactide)/chitosan/polypyrrole complex membranes is reported. Using poly(DL -lactide)/chitosan blends as matrices and polypyrrole as a conductive component, several kinds of membranes with various compositions are prepared. A percolation threshold of polypyrrole as low as 1.8 wt.-% is achieved for some membranes by controlling the chitosan proportion between 40 and 50 wt.-%. SEM images exhibit that the membranes with a low percolation threshold show a two-phase structure which consists of poly(DL -lactide) and chitosan phases. Dielectric measurements indicate that there is limited miscibility between the poly(DL -lactide) and chitosan but polypyrrole is nearly immiscible with the other two components. Based on the structural characteristics of the membranes, the polypyrrole particles are suggested to be localized at the interface between two phases. Dependence of conductivity of complex membranes on the PPy content. (,) PDLLA/PPy, (,) PDLLA/ch(10)/PPy, (,) PDLLA/ch(20)/PPy, (,) PDLLA/ch(30)/PPy, (,) PDLLA/ch(40)/PPy, and (,) PDLLA/ch(50)-PPy. [source]

Study of prelocalized graphite/styrene acrylonitrile conducting composites for device applications

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2006
V. K. Sachdev
Abstract Conductive polymer composites were prepared by compression molding of prelocalized graphite on to styrene acrylonitrile (SAN) particles. The electrical conductivity is found to be strongly dependent on the graphite content. Three different series were prepared for different processing and material parameters. A low percolation threshold has been noticed when only 1 wt% of graphite is incorporated. Resistivity as low as ,14 , cm has been achieved in a composite with SAN resin particles of 180,212 µm size and graphite 10,20 µm at 90 °C, 105 MPa and 15 min. An electrically conducting network of graphite channels has been observed using scanning electron microscopy. V,I characteristic reveals that at a lower percentage of graphite the increase in current with increase in electric field is due to the hopping/tunneling of electrons, while for higher percentages of graphite ohmic behavior similar to metals has been observed. The data has been analyzed using percolation model. The value of the exponent t that determines the increase in electrical conductivity above the percolation threshold is found to be close to the values given in the literature. The theoretically calculated values of conductivity are found to be in satisfactory agreement with the experimental ones. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Fabrication and electrical properties of CNT/PP conductive composites with low percolation threshold by solid state alloying

POLYMER COMPOSITES, Issue 6 2010
D.L. Gao
The carbon nanotube/polypropylene conductive composites with a percolation threshold as low as 0.25 wt% were fabricated by solid state alloying. This solid state alloying method uses the super-high speed mechanical shearing (at 10,000 rpm) to process the entangled catalytically grown carbon nanotubes (CNTs) and the polymer matrix in solid state. The electrical properties of the nanocomposites and the structure and distribution of CNTs were investigated. The results indicated that via the shear-intensive process, CNTs were truncated and dispersed effectively, and their length could be controlled properly to fully exert the advantage of high aspect ratios (length-to-diameter ratios). At the same time, a linear structure conductive network which may considerably lower the percolation threshold was also formed by this method. Moreover, the CNTs could be further dispersed under the action of thermo energy provided by increasing the processing temperature. The super-high speed solid state alloying method is a favorable approach for the production of low percolation threshold conductive composites of CNTs filled high viscosity resins. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source]

Electrical and mechanical properties of multi-walled carbon nanotubes reinforced PMMA and PS composites

POLYMER COMPOSITES, Issue 7 2008
R.B. Mathur
The use of multi-walled carbon nanotubes (MWCNT) as reinforcing material for thermoplastic polymer matrices, polymethyl methacrylate (PMMA), and polystyrene (PS) has been studied. MWCNT were synthesized by chemical vapor deposition (CVD) technique using ferrocene-toluene mixture. As-prepared nanotubes were ultrasonically dispersed in toluene and subsequently dispersed in PMMA and PS. Thin polymer composite films were fabricated by solvent casting. The effect of nanotube content on the electrical and mechanical properties of the nanocomposites was investigated. An improvement in electrical conductivity from insulating to conducting with increasing MWCNT content was observed. The carbon nanotube network showed a classical percolating network behavior with a low percolation threshold. Electromagnetic interference (EMI) shielding effectiveness value of about 18 dB was obtained in the frequency range 8.0,12 GHz (X-band), for a 10 vol% CNT loading. An improved composite fabrication process using casting followed by compression molding and use of functionalized MWCNT resulted in increased composites strength. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source]

Facile High-Yield Synthesis of Polyaniline Nanosticks with Intrinsic Stability and Electrical Conductivity

CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2008
Xin-Gui Li Prof.
Abstract Chemical oxidative polymerization at 15,°C was used for the simple and productive synthesis of polyaniline (PAN) nanosticks. The effect of polymerization media on the yield, size, stability, and electrical conductivity of the PAN nanosticks was studied by changing the concentration and nature of the acid medium and oxidant and by introducing organic solvent. Molecular and supramolecular structure, size, and size distribution of the PAN nanosticks were characterized by UV/Vis and IR spectroscopy, X-ray diffraction, laser particle-size analysis, and transmission electron microscopy. Introduction of organic solvent is advantageous for enhancing the yield of PAN nanosticks but disadvantageous for formation of PAN nanosticks with small size and high conductivity. The concentration and nature of the acid medium have a major influence on the polymerization yield and conductivity of the nanosized PAN. The average diameter and length of PAN nanosticks produced with 2,M HNO3 and 0.5,M H2SO4 as acid media are about 40 and 300,nm, respectively. The PAN nanosticks obtained in an optimal medium (i.e., 2,M HNO3) exhibit the highest conductivity of 2.23,S,cm,1 and the highest yield of 80.7,%. A mechanism of formation of nanosticks instead of nanoparticles is proposed. Nanocomposite films of the PAN nanosticks with poly(vinyl alcohol) show a low percolation threshold of 0.2,wt,%, at which the film retains almost the same transparency and strength as pure poly(vinyl alcohol) but 262,000 times the conductivity of pure poly(vinyl alcohol) film. The present synthesis of PAN nanosticks requires no external stabilizer and provides a facile and direct route for fabrication of PAN nanosticks with high yield, controllable size, intrinsic self-stability, strong redispersibility, high purity, and optimizable conductivity. [source]

Single-walled carbon nanotube/ultrahigh-molecular-weight polyethylene composites with percolation at low nanotube contents

POLYMER ENGINEERING & SCIENCE, Issue 12 2009
Brian P. Grady
To mix single-walled carbon nanotubes (SWCNTs) with a polymer and to achieve low percolation thresholds, a low-viscosity liquid has been required in order to achieve sufficiently good dispersion. In this article, data are presented which show that percolation occurs at ,0.14 wt % carbon nanotubes and the dispersion procedure does not involve dispersing the SWCNTs in a low-viscosity liquid. Specifically, ultrahigh-molecular-weight polyethylene powder was mixed with a powder containing nanotubes and catalyst support, e.g., the powder contains 93% silica and 7% SWCNTs. The powder blend is compression molded into sheets using high pressure and temperature. Because of the very high viscosity of the resin, the nanotube/silica mixture largely stays segregated at the interface as shown by scanning electron microscopy. A significant drop in tensile properties (modulus, tensile strength, and elongation at break) occurs with filler incorporation. Non isothermal crystallization measurements indicate that this filler does not nucleate crystallinity when mixed in this manner; although there is a definite sharpening of the melt endotherm indicating that crystallites with smaller lamellar thicknesses are reduced significantly with filler addition. The addition of filler also slightly reduces the overall fractional crystallinity measured after a constant cooling rate. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]