scholarly journals The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO2

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1469
Author(s):  
Mohammed Mostafa Adnan ◽  
Inger-Emma Nylund ◽  
Aleksander Jaworski ◽  
Sverre Hvidsten ◽  
Marit-Helen Glomm Ese ◽  
...  
Keyword(s):  
Coupling Agent ◽  
Free Space ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Inorganic Nanoparticles ◽  
Sio2 Content ◽  
Electrode Polarization ◽  
Fractal Structures ◽  
Space Length

Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO2 nanocomposites was employed, where surface-functionalized SiO2 (up to 5 wt.%) is synthesized directly in the epoxy. The dispersion of SiO2 was found to be affected by both the pH and the coupling agent used in the synthesis. Hierarchical clusters of SiO2 (10-60 nm) formed with free-space lengths of 53–105 nm (increasing with pH or SiO2 content), exhibiting both mass and surface-fractal structures. Reducing the amount of coupling agent resulted in an increase in the cluster size (~110 nm) and the free-space length (205 nm). At room temperature, nanocomposites prepared at pH 7 exhibited up to a 4% increase in the real relative permittivity with increasing SiO2 content, whereas those prepared at pH 11 showed up to a 5% decrease with increasing SiO2 content. Above the glass transition, all the materials exhibited low-frequency dispersion effect resulting in electrode polarization, which was amplified in the nanocomposites. Improvements in the dielectric properties were found to be not only dependent on the state of dispersion, but also the structure and morphology of the inorganic nanoparticles.

Preparation and characterization of silicone rubber/graphene nanosheets nanocomposites by in-situ loading of the coupling agent

2019 ◽  
Vol 53 (24) ◽  
pp. 3459-3468
Author(s):  
Elnaz Esmizadeh ◽  
Mostafa Arjmandpour ◽  
A Vahidifar ◽  
Ghasem Naderi ◽  
Charles Dubois
Keyword(s):  
Mechanical Properties ◽  
Silicone Rubber ◽  
Coupling Agent ◽  
Loss Modulus ◽  
Graphene Nanosheets ◽  
Low Frequency ◽  
Cure Kinetics ◽  
Relaxation Processes ◽  
Tensile Data

Inexpensive approach to fully disperse graphene nanosheet (GNS) in silicone rubber (SR) by the addition of (3-Aminopropyl) triethoxysilane (APTES) as the coupling agent is presented in this study. The effects of GNS loading and presence of APTES on the cure characteristics, dynamic-mechanical, rheological and mechanical properties of the resulting SR compounds were systematically studied by rheometry, DMTA and tensile testing, respectively. The obtained results were correlated with the microstructure of the samples investigated by SEM and TEM analyses. Vulcanization curves revealed that the GNS and the coupling agent had an accelerating effect on the cure kinetics of the SR compounds leading to a steady decrease in scorch time and optimum cure time along with a gradual increase in the effective torque value. Morphological results showed that the GNSs could disperse more homogeneously within SR matrix using a simple solution mixing approach by in-situ loading of APTES. DMTA results showed restricted relaxation processes in GNS-reinforced SR systems in comparison with the pure SR, with more pronounced effect for the system containing APTES owing to improved interactions between graphene and SR which prevented the molecular mobility of neighboring chains of SR matrix. The tensile data demonstrated about 20% rise of modulus in the GNS-filled rubber nanocomposites in the presence of APTES. Low-frequency rheological properties including the storage modulus (G′), the loss modulus (G″), and complex shear viscosity (η*) showed a significant increase of about 10-fold, 75% and 20%, respectively, with the incorporation of APTES and GNS. Thus it could be expected that APTES had a substantial potential to be applied in-situ as the coupling agent to fabricate SR/GNS nanocomposites with exfoliated GNS morphology and increased the rheological and mechanical properties.

scholarly journals Magnetic, Thermal and Electrical Transport Properties of o-Substituted Polyanilines Encapsulated with Fe2O3 Nanoparticles

2019 ◽  
Vol 32 (2) ◽  
pp. 265-270
Author(s):  
R. Suganthi ◽  
S. Padmaja ◽  
S. Jhancy Mary
Keyword(s):  
Dielectric Constant ◽  
Electrical Transport ◽  
Oxidative Polymerization ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Decomposition Temperature ◽  
Spectroscopic Techniques ◽  
Electrical Transport Properties ◽  
Frequency Independent

Poly(2-nitroaniline), poly(2-nitroaniline)-Fe2O3 and poly(2-methylaniline)-Fe2O3 nanocomposites synthesized by in situ chemical oxidative polymerization technique were characterized by XRD, thermal (TGA and DTA) and FTIR & UV-visible spectroscopic techniques. The thermal stability was confirmed by the integral procedural decomposition temperature (IPDT) and oxidation index (OI) calculations. The electrical conductivity and dielectric properties were also investigated. At low frequency region, the dielectric constant decreases with increase in frequency due to electrical relaxation process. At high frequencies, dielectric constant is independent of frequency. At low frequency, there was strong frequency dispersion of permittivity and above 3 Hz, a frequency independent behaviour in permittivity was observed. The materials exhibit ferromagnetic behaviour.

Magnetic Permeability and Relaxation Frequency in High Frequency Magnetic Materials.

2001 ◽  
Vol 674 ◽  
Author(s):  
M.I. Rosales ◽  
H. Montiel ◽  
R. Valenzuela
Keyword(s):  
High Frequency ◽  
Domain Walls ◽  
Magnetocrystalline Anisotropy ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Anisotropy Constant ◽  
Relaxation Frequency ◽  
Resonance Relaxation ◽  
Frequency Behavior

ABSTRACTAn investigation of the frequency behavior of polycrystalline ferrites is presented. It is shown that the low frequency dispersion (f < 10 MHz) of permeability is associated with the bulging of pinned domain walls, and has a mixed resonance-relaxation character, closer to the latter. It is also shown that there is a linear relationship between the magnetocrystalline anisotropy constant, K1, and the relaxation frequency. The slope of this correlation depends on the grain size. Such a relationship could allow the determination of this basic parameter from polycrystalline samples.

Mineral interfacial processes in the method of induced polarization

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 1105-1114 ◽  
Author(s):  
James D. Klein ◽  
Tom Biegler ◽  
M.D. Horne
Keyword(s):  
Frequency Domain ◽  
Diffusion Layer ◽  
Electrode Potential ◽  
Rotation Speed ◽  
Low Frequency ◽  
Rotating Disk ◽  
Active Species ◽  
Hydrodynamic Theory ◽  
Electrode Polarization ◽  
Disk Electrodes

A phenomenological laboratory investigation has been conducted of the IP response of pyrite, chalcopyrite, and chalcocite. The technique that was used is standard in electrochemistry and employs rotating disk electrodes. The effect of rotation is to stir the electrolyte and thus to restrict the maximum distance available for diffusion of electroactive aqueous species. For high rotation speed and low excitation frequencies, the mean diffusion length exceeds the thickness of the diffusion layer. The net effect is to reduce the electrode impedance at low frequency. The thickness of the diffusion layer and thus the impedance at low frequency can be controlled by the rotation speed. Measurements using rotating disk electrodes have been conducted in both the time domain and the frequency domain. For both pyrite and chalcopyrite, the results were the same: no dependence on rotation was observed. For frequency domain measurements with chalcocite, a strong dependence on rotation was observed. The interpreted diffusion layer thickness was found to depend on rotation speed to the [Formula: see text] power, in agreement with results predicted by hydrodynamic theory. The results of this study imply that there are two physical processes responsible for electrode polarization in the IP method. For chalcocite and perhaps other related copper sulfide minerals, the probable mechanism is diffusion of copper ions in the groundwater. In case, the phenomenon is correctly described by the Warburg impedance. Chalcocite’s distinctive response is thought to be related to its forming a reversible oxidation‐reduction couple with cupric ions in solution. No other common sulfide mineral forms a reversible couple with its cations in solution. For the other minerals of this study, the lack of dependence on rotation implies that diffusion of active species in the electrolyte is not the controlling process. Possible alternate mechanisms include surface controlled processes such as surface diffusion or adsorption phenomena. Ancillary data obtained during this study indicate the interface impedance of chalcopyrite is proportional to the electrode potential which in turn can be controlled by rotation speed, electrolyte composition, or application of an external dc current or voltage. This implies that the surface concentration of active species is dependent on electrode potential.

Preparation and Properties of the Polystyrene/Alumina Nanocomposites

2012 ◽  
Vol 557-559 ◽  
pp. 519-522
Author(s):  
Xu Man Wang ◽  
Cai Ning Zhang
Keyword(s):  
Molecular Weight ◽  
Thermal Resistance ◽  
Coupling Agent ◽  
Silane Coupling Agent ◽  
In Situ Polymerization ◽  
Average Molecular Weight ◽  
Experimental Results ◽  
Solvent Resistance ◽  
Silane Coupling

Silane coupling agent KH-570 was applied to modify the surface capability of the alumina (Al2O3). The modified Al2O3were dispersed in styrene. The in-situ polymerization was used to prepare the polystyrene/alumina (PS/Al2O3) composites, in which azodiisobutyronitrile (AIBN) was used as initiator. FTIR, DSC and TG were applied to characterize the prepared composites. The solvent resistance, thermal resistance of the composites and the average molecular weight of PS in PS/Al2O3nanocomposites were studied. The experimental results demonstrated that the solvent resistance of PS/Al2O3nanocomposites was improved by the adding of Al2O3nanoparticles. The thermal resistance of the composites increased with the increasing of the Al2O3content. Meanwhile, the molecular weight of PS in the composites increased with the increasing of the Al2O3content.

Negative Permittivity Behavior in Silver/Polyaniline Metacomposites Induced by the Low-Frequency Plasmonic Oscillation

2021 ◽  
Author(s):  
Jiahong Tian ◽  
Runhua Fan ◽  
Zongxiang Wang ◽  
Jiahao Xin ◽  
Zhongyang Wang
Keyword(s):  
Synthesis Method ◽  
Low Frequency ◽  
In Situ Synthesis ◽  
Negative Permittivity ◽  
Free Electrons ◽  
Dominant Effect ◽  
Equivalent Circuit Analysis ◽  
Inductive Character ◽  
Percolation Network

Abstract Silver/polyaniline (Ag/PANI) composites were prepared by an in-situ synthesis method. Interestingly, the permittivity changed from positive to negative along with the formation of percolation network. The plasma oscillations of free electrons from the network made a dominant effect on the negative permittivity behavior. Further investigation based on equivalent circuit analysis revealed that the composites with negative permittivity presented inductive character. The epsilon-negative composites can be applied to electromagnetic shielding, absorbing and attenuation.

scholarly journals Frequency dispersion reveals chromophore diversity and colour-tuning mechanism in parrot feathers

2018 ◽  
Vol 5 (7) ◽  
pp. 172010 ◽  
Author(s):  
Jonathan E. Barnsley ◽  
Elliot J. Tay ◽  
Keith C. Gordon ◽  
Daniel B. Thomas
Keyword(s):  
Frequency Dispersion ◽  
Animal Coloration ◽  
Molecular Conformations ◽  
Tuning Mechanism ◽  
Resonance Raman Spectra ◽  
Molecule Interactions ◽  
Yellow Region ◽  
Colour Tuning

Variation in animal coloration is often viewed as the result of chemically distinct pigments conferring different hues. The role of molecular environment on hue tends to be overlooked as analyses are mostly performed on free pigments extracted from the integument. Here we analysed psittacofulvin pigments within parrot feathers to explore whether the in situ organization of pigments may have an effect on hue. Resonance Raman spectra from a red region of a yellow-naped amazon Amazona auropalliata tail feather show frequency dispersion, a phenomenon that is related to the presence of a range of molecular conformations (and multiple chromophores) in the pigment, whereas spectra from a yellow region on the same feather do not show the same evidence for multiple chromophores. Our findings are consistent with non-isomeric psittacofulvin pigments behaving as a single chromophore in yellow feather barbs, which implies that psittacofulvins are dispersed into a structurally disordered mixture in yellow feathers compared with red feathers. Frequency dispersion in red barbs may instead indicate that pigments are structurally organized through molecule–molecule interactions. Major differences in the hues of parrot feathers are thus associated with differences in the organization of pigments within feathers.

Volume low-frequency dispersion in a semi-insulating system

1988 ◽  
Vol 23 (2) ◽  
pp. 209-213 ◽  
Author(s):  
A.K. Jonscher ◽  
L. Levesque
Keyword(s):  
Low Frequency ◽  
Frequency Dispersion

Correlation of free space length and surface energy of epoxy nanocomposites to surface tracking

2018 ◽  
Vol 25 (6) ◽  
pp. 2129-2138 ◽  
Author(s):  
M. Suchitra ◽  
N. M. Renukappa ◽  
C. Ranganathaiah ◽  
J. Sundara Rajan
Keyword(s):  
Surface Energy ◽  
Free Space ◽  
Epoxy Nanocomposites ◽  
Space Length ◽  
Surface Tracking
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