共查询到20条相似文献,搜索用时 15 毫秒
1.
在聚合物基体中掺入少量的层状硅酸盐所制备的聚合物/粘土纳米复合材料,其阻隔性能明显地优于纯聚合物及其传统的复合材料。实验及分析结果表明,聚合物/粘土纳米复合材料的微观结构和阻隔性能主要受控于粘土剥离后的径厚比.一简单的重整化群模型被用来评估粘土几何因素(诸如径厚比、取向、剥离程度等)对聚合物/粘土纳米复合材料阻隔性能的影响,所得到的逾渗阈值及最佳粘土含量与实验结果吻合。 相似文献
2.
The barrier properties of polymer-clay nanocomposites, with far less inorganic contents of layered-silicate fillers, are remarkably superior to those of neat polymers or their conventional counterparts. A simple renormalization group model is proposed to assess the influence of geometric factors (such as aspect ratio, orientation, and extent of exfoliation) of layered-silicate fillers on the barrier properties of polymer-clay nanocomposites. The results show that the aspect ratio of exfoliated silicate platelets has a critical role in controlling the microstructure of polymer-clay nanocomposites and their barrier properties. The estimated percolation thresholds of clay content for minimum permeability are in good agreement with experimental data. 相似文献
3.
《Current Applied Physics》2009,9(5):956-959
Novel Ag–BaTiO3/PVDF (polyvinylidene fluoride) three-component nanocomposites and traditional BaTiO3/PVDF two-component nanocomposites were prepared by the same procedures. The dielectric properties of these two kinds of composites were compared. The results showed that the kind of three-component nanocomposites had better dielectric properties. The energy density of such kind of composites could reach nearly 10 J/cm3, which indicated that these nanocomposites could be used as the dielectric layers of pulse-power capacitors. The Coulomb blockade effect was used to explain the dielectric breakdown properties and the resistivities under high electric field of such new kind of nanocomposites. 相似文献
4.
Electrical and dielectric properties of conducting polypyrrole–wide band gap silica (PPY–SiO2) nanocomposites have been investigated as a function of temperature and frequency for different concentrations of polypyrrole.
The average grain size of the nanocomposites is in the range of 40–80 nm. Impedance spectra reveal two distorted semicircles
corresponding to grain and grain boundary effects. The magnitude of conductivity and its temperature variation are significantly
different from polypyrrole and silica. A very large dielectric constant of about 4800 at 30 kHz and at room temperature has
been observed for the highest concentration of silica. Inhomogeneous behavior of nanocomposites gives rise to high dielectric
constant. 相似文献
5.
The nanocomposites of conducting polyaniline are prepared by intercalating into the
layers of vanadium pentoxide (V2O5) xerogel. The intercalation is
confirmed by the observation of lattice expansion of V2O5 xerogel. Dc
conductivity of the gel follows Arrhenius type temperature dependence while the
nanocomposites exhibit three dimensional variable range hopping. The ac conductivity
and dielectric properties are extensively studied at low temperature up to the
frequency of 10 MHz. Two semicircles in Cole-Cole plot of impedance are found for
the nanocomposites. The ac conductivity spectra reveal three frequency regions. The
frequency exponent in the lower frequency region is nearer to 2. The dielectric
response exhibit broad spectra which are analyzed by Cole-Cole distribution
function. The peak frequency of dielectric spectra appears at the first cross over
frequency of conductivity spectra. 相似文献
6.
A. B. Granovsky Y. E. Kalinin A. V. Sitnikov O. V. Stognei 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(9):1134-1135
The effect heat treatment has on the transport properties of metal–insulator nanocomposites of amorphous structure is investigated. An increase in the electric resistance and magnetoresistance after the heat treatment of nanocomposites in which the concentration of the metal phase lies below the percolation threshold is established. The observed changes are due to structural relaxation of the amorphous dielectric matrix. 相似文献
7.
Silica/epoxy composites have been widely used in functional electric device applications. Silica nanoparticles, both unmodified and modified with the coupling agent KH-550, were used to prepare epoxy composites. Dielectric measurements showed that nanocomposites exhibit a higher dielectric constant than the control sample, and had more obvious dielectric relaxation characteristics. Results showed that particle surface properties have a profound effect on the dielectric behavior of the nanocomposites. These characteristics are attributed to the local ununiformity of the microstructure caused by the large interface area and the interaction between the filler and the matrix. This phenomenon is explained in terms of prolonging chemical chains created during the curing process. The mechanism is discussed with measurements of X-ray diffraction (XRD) and Fourier transform infrared (FTIR). 相似文献
8.
High-Temperature Dielectric Response and Multiscale Mechanism of SiO2/Si3N4 Nanocomposites
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The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300°C at 9.0GHz are measured by the resonant cavity method. The SiO2/Si3N4 nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO2/Si3N4 on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures. 相似文献
9.
Enhanced dielectric properties of polyvinylidene fluoride with addition of SnO2 nanoparticles
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In this letter, SnO2/polyvinylidene fluoride (PVDF) nanocomposites with outstanding dielectric properties were fabricated. The SEM and TEM images showed that SnO2 nanoparticles with size of 5–7 nm dispersed homogeneously in polymer matrix. The significantly improved dielectric constant was well explained by percolation theory. The nanocompo‐ sites can retain a certain value of breakdown field. The maximum energy density of SnO2/PVDF nanocomposites was 5.4 J/cm3, two times that of the pure polyvinylidene fluoride. These findings suggest that SnO2/PVDF nanocomposites are suitable candidates for energy storage applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
10.
Herman A. Lopez X. Linda Chen Samson A. Jenekhe Philippe M. Fauchet 《Journal of luminescence》1998,80(1-4):115-118
In this report we demonstrate control over porous silicon (PSi) emission properties by changing the dielectric environment surrounding the silicon crystallites, as well as provide information on the effects of pore infiltration of PSi. This is achieved by making PSi–polymer nanocomposites by diffusing or polymerizing a range of varying dielectric constant polymers into the pores. The degree of modification in photoluminescence (PL) depends on the dielectric constant of the polymers. By increasing the dielectric constant of the environment surrounding the crystallites, a blue shift in PL as high as 222 meV has been observed. The blue shift is attributed to the high dielectric constant of the polymers relative to PSi, which causes a partial screening of the excitons allowing the excitonic levels to shift closer to the bandgap. The shift in excitonic levels increases when the dielectric constant of the polymer increases. PSi–polymer nanocomposites also exhibit an increase in PL intensity, which suggest that the inert infiltrated polymers are able to passivate existing nonradiative channels. 相似文献
11.
The fabrication of high quality thin films of poly (vinylidene fluoride) embedded with multiwalled carbon nanotubes using pulsed laser deposition technique is reported. The prepared films were characterized for structural, morphology and dielectric properties. The morphology analysis revealed uniform dispersion of multiwalled carbon nanotubes throughout the polymer matrix. X-ray diffraction results suggested that the poly (vinylidene fluoride) film is in amorphous phase while addition of multiwalled carbon nanotubes showed presence of crystalline peaks in the nanocomposites films. It was interesting to note that the nanocomposite films exhibits significant enhancement of the ferroelectric β-phase as evidenced by the X-ray diffraction and Fourier transform infrared spectroscopy results. The dielectric analysis shows a remarkable enhancement in the dielectric permittivity of nanocomposites with lower loss and conductivity level. The results can be attributed to the formation of minicapacitor network and relatively higher percolation threshold in the nanocomposites. 相似文献
12.
Santosh D. Wanjale 《Journal of Macromolecular Science: Physics》2013,52(6):1053-1064
Linear viscoelastic properties and dielectric behavior of poly(1‐butene)/multiwalled carbon nanotube (MWCNT) nanocomposites were investigated. Dynamic mechanical analysis showed significant increase in storage modulus in the rubbery regime. The tan δ peak temperature remained constant; however, the peak intensity was lowered for the nanocomposites. In melt rheological studies the nanocomposites showed a shift in crossover frequency to the lower side, suggesting delayed relaxation of the molecular chains in the presence of MWCNT and this shift was found to depend on the content of MWCNT. The dielectric constant increased from 2.2 to 70 for the nanocomposite with 7 wt. % MWCNT. The electrical conductivity increased significantly, from 10?15 to 10?3 S/cm. The results of rheology and dielectric studies indicate that a percolation network is formed that is responsible for the observed changes. 相似文献
13.
We propose a simple semiphenomenological model to describe the dynamics of polymer melt intercalation in the gallery between the adjacent clay sheets in polymer-clay nanocomposites. Within this model, the intercalation process is driven by the motion of localized excitations ("kinks") which open up the tip between the clay sheets. These kinks belong to a novel type of solitonlike excitations that appear due to the interplay between the double-well potential of the clay-clay long-range interaction, bending elasticity of the sheets, and external shear force. We find that the kink solutions can exist only if applied shear is sufficiently strong, in a qualitative agreement with experimental data. 相似文献
14.
S. V. Baryshnikov E. V. Charnaya Yu. A. Shatskaya A. Yu. Milinskiy M. I. Samoilovich D. Michel C. Tien 《Physics of the Solid State》2011,53(6):1212-1215
The temperature dependence of the linear permittivity and the third harmonic generation amplitude of nanocomposites representing
nanoporous silica matrices (opal matrix and SBA-15) with triglycine sulfate embedded in pores has been studied in the region
of the ferroelectric phase transition. A broadening of the phase transition and an increase its temperature in comparison
with bulk triglycine sulfate have been revealed. The latter becomes more significant as the pore size decreases. It has been
shown that the nonlinear dielectric properties of nanocomposites near the phase transition differ significantly from the properties
of bulk triglycine sulfate. 相似文献
15.
F. Miomandre F. Chandezon B. Lama J. Besnardière M. Routier A. Brosseau P. Audebert 《Journal of nanoparticle research》2011,13(2):879-886
A direct route to polypyrrole–silica core–shell nanoparticles with diameters in the 150–300 nm range is described to design
new nanocomposites, in which the conducting part is wrapped by an external silica shell in order to obtain finally neutral
conductive nanoparticles. The nanocomposites are characterized by SEM, FTIR, electrochemistry and thermal gravimetric analysis,
demonstrating that the external silica shell actually insulates the conjugated polymer from the outer medium. In a second
step, the nanocomposites are coated with an additional PDMS layer. The electrorheological properties of the ink made by dispersion
of these final nanoparticles in a low dielectric constant fluid are checked in a dielectrophoretic device, in which the motion
of the particles induced by an external electric field can be used to monitor a switch of the light transmission properties
with a low voltage threshold. 相似文献
16.
An epoxy network structure made of diglycidylether of bisphenol-A and diamino diphenylsulfone was modified by adding various amounts of an epoxy functionalized polyhedral oligomeric silsesquioxane. The obtained nanocomposites were characterized in terms of optical and dielectric properties. The UV-absorption spectra were collected in the wavelength range of 400–800 nm. The optical data were analyzed in terms of absorption formula for non-crystalline materials. The optical energy gap and other basic constants, such as energy tails, dielectric constants, refractive index and optical conductivity, were determined and showed a clear dependence on the POSS concentration. It was found that the optical energy gap for the neat epoxy resin is less than for nanocomposites, and it decreases with increase in the POSS content. The refractive index of nanocomposites was determined from the calculated values of absorption and reflectance. It was found that the refractive index and the dielectric constants increased with increase in the POSS concentration. The optical conductivity, which is a measure of the optical absorption, increased with the POSS content. Furthermore, it was found that the glass transition temperature and the optical energy gap correlate well with the POSS filler concentration. 相似文献
17.
Dendrite-shaped PbS has been successfully synthesized using hydrothermal method on a large scale. The formation of dendrite-shaped PbS was confirmed by scanning electron microscopy (SEM). A detailed study of variations in dielectric properties on frequency and temperature shows that composites of PVDF and dendrite-shaped PbS have significantly higher dielectric constant than PVDF/PbS nanoparticles (NP) nanocomposites due to low percolation threshold. 相似文献
18.
Lin Zhang Xiaobing Shan Peixuan Wu Z.-Y. Cheng 《Applied Physics A: Materials Science & Processing》2012,107(3):597-602
Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu3Ti4O12 (CCTO) particles are used as filler and P(VDF?CTrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50?vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50?vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (??340?K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles. 相似文献
19.
Cernea Marin Trupina Lucian Vasile Bogdan S. Trusca Roxana Chirila Cristina 《Journal of nanoparticle research》2013,15(7):1-7
The results of investigations of porous glasses (PG) and porous glasses–ammonium hydrogen sulfate ferroelectric nanocomposites (AHS–PG) are presented. On the basis of dielectric and calorimetric measurements it was shown that in the AHS–PG nanocomposites with average pore size of 44, 68, 95, and 320 nm the anomalies of dielectric permittivity and specific heat similar to those in bulk crystals AHS are observed. An influence of the mean value of pores sizes on the ferroelectric phase transition temperatures of AHS nanocrystals embedded into the porous matrices was determined. It was shown that in AHS–PG dispersion of the dielectric permittivity is observed in both para- and ferro-electric phases and above room temperature AHS–PG nanocomposites exhibit the ionic conductivity. 相似文献
20.
I. Fina V. Laukhin L. Fàbrega F. Sánchez 《Journal of magnetism and magnetic materials》2009,321(11):1795-1798
We report on the dielectric characterization of CoFe2O4-BaTiO3 nanocomposites grown by rf sputtering. Dielectric properties have been analyzed for samples grown at different deposition temperatures and with different thicknesses. Impedance spectroscopy data has been analyzed by fitting to an equivalent circuit and different contributions have been identified. Correlations between dielectric properties and deposition temperature and thickness have been established. 相似文献