Polysiloxanes Modified with Different Types and Contents of Polar Groups: Synthesis, Structure, and Thermal and Dielectric Properties

2021 ◽  
Author(s):  
Yauhen Sheima ◽  
Yulia Yuts ◽  
Holger Frauenrath ◽  
Dorina M. Opris
Keyword(s):  
Dielectric Properties ◽  
Polar Groups ◽  
Different Types

The Dependence of Dielectric Properties on Crosslink Density of Rubbers

1978 ◽  
Vol 51 (1) ◽  
pp. 72-80 ◽  
Author(s):  
R. Bakule ◽  
A. Havránek
Keyword(s):  
Dielectric Properties ◽  
Natural Rubber ◽  
Crosslink Density ◽  
Unit Volume ◽  
Volume Distribution ◽  
Dicumyl Peroxide ◽  
Frequency Range ◽  
Polar Groups ◽  
Main Transition ◽  
Macroscopic Parameters

Abstract The dielectric properties of natural rubber, synthetic polyisoprene, andpolybutadiene samples crosslinked with sulfur and of natural rubber samplescrosslinked simultaneously with sulfur and dicumyl peroxide were studied. Inthe investigated systems, the number of polar groups in unit volume and thecrosslink density may be changed independently over relatively wide ranges.The measurements were performed in the frequency range from 101 to 105 Hzat various temperatures, and macroscopic parameters describing the dielectricproperties of the samples were evaluated. The position and intensity of thedielectric dispersion peak in the main transition zone is only slightly dependenton the crosslink density of the samples. These two values are mainly influencedby the amount of combined sulfur, or more generally, by the number and thedipole moments of polar groups in the sample. The influence of crosslink densityon the width of the absorption curve is very strong; the width increases withincreasing crosslink density. The possibility of explaining this effect in termsof the dependence of the free volume distribution function on crosslink densityis discussed.

Influence of various multilayer LTCC systems on dielectric properties’ stability in GHz frequency range

2016 ◽  
Vol 33 (3) ◽  
pp. 136-140 ◽  
Author(s):  
Tibor Rovensky ◽  
Alena Pietrikova ◽  
Igor Vehec ◽  
Martin Kmec
Keyword(s):  
Dielectric Properties ◽  
Design Methodology ◽  
Middle Layer ◽  
Ring Resonators ◽  
Frequency Range ◽  
Content Type ◽  
Different Types ◽  
Good Repeatability ◽  
Microstrip Ring ◽  
Multilayer Substrate

Purpose The purpose of this paper is to create multilayer substrate (composite) from various low temperature co-fired ceramic (LTCC) substrates by their mutual combinations and to analyse influence of these multilayer substrates on dielectric properties in GHz frequency range. Design/methodology/approach GreenTape 951, GreenTape 9K7 and Murata LFC were used to create compound multilayer substrates that include three layers: middle layer is from Murata LFC, and both upper and bottom layers are either from GreenTape 951 or GreenTape 9K7. Shrinkage in all x-, y- and z-axes of all substrates including multilayer substrates were analysed, and influence of different shrinkage on dielectric properties was examined by microstrip ring resonators applied on all mentioned of substrates. Findings The middle layer of Murata LFC has significant influence on shrinkage value of composites which has a good repeatability and minimalizes problems with design of multilayer LTCC devices. Impact of middle layer from Murata LFC on dielectric constant is not significant, but on the other hand Q factor (loss tangent) of these composites is increased according to inhomogeneity between single LTCC layers, especially at frequency around 6 GHz. Originality/value The novelty of this work lies in creating multilayers systems from different types of LTCC substrates to find combination with the most suitable physical and dielectric properties for various purposes in GHz range applications.

scholarly journals Finite-element analysis of microwave scattering from a three-dimensional human head model for brain stroke detection

2018 ◽  
Vol 5 (7) ◽  
pp. 180319
Author(s):  
Awais Munawar Qureshi ◽  
Zartasha Mustansar ◽  
Samah Mustafa
Keyword(s):  
Finite Element ◽  
Dielectric Properties ◽  
Electric Field ◽  
Three Dimensional ◽  
Human Head ◽  
Head Model ◽  
Different Types ◽  
Brain Stroke ◽  
Human Head Model ◽  
Brain Stroke Detection

In this paper, a detailed analysis of microwave (MW) scattering from a three-dimensional (3D) anthropomorphic human head model is presented. It is the first time that the finite-element method (FEM) has been deployed to study the MW scattering phenomenon of a 3D realistic head model for brain stroke detection. A major contribution of this paper is to add anatomically more realistic details to the human head model compared with the literature available to date. Using the MRI database, a 3D numerical head model was developed and segmented into 21 different types through a novel tissue-mapping scheme and a mixed-model approach. The heterogeneous and frequency-dispersive dielectric properties were assigned to brain tissues using the same mapping technique. To mimic the simulation set-up, an eight-elements antenna array around the head model was designed using dipole antennae. Two types of brain stroke (haemorrhagic and ischaemic) at various locations inside the head model were then analysed for possible detection and classification. The transmitted and backscattered signals were calculated by finding out the solution of the Helmholtz wave equation in the frequency domain using the FEM. FE mesh convergence analysis for electric field values and comparison between different types of iterative solver were also performed to obtain error-free results in minimal computational time. At the end, specific absorption rate analysis was conducted to examine the ionization effects of MW signals to a 3D human head model. Through computer simulations, it is foreseen that MW imaging may efficiently be exploited to locate and differentiate two types of brain stroke by detecting abnormal tissues’ dielectric properties. A significant contrast between electric field values of the normal and stroke-affected brain tissues was observed at the stroke location. This is a step towards generating MW scattering information for the development of an efficient image reconstruction algorithm.

Test of the Applicability of Dielectric Loss Measurements to the Study of the Aging of Pure-Gum Rubber Mixtures

1955 ◽  
Vol 28 (2) ◽  
pp. 420-428 ◽  
Author(s):  
P. Henri-Robert
Keyword(s):  
Oxidation Products ◽  
Protective Agent ◽  
Broad Distribution ◽  
Valuable Data ◽  
Dielectric Absorption ◽  
Vulcanized Rubber ◽  
Polar Groups ◽  
Different Types ◽  
High Level

Abstract The measurement of the dielectric properties at radioelectric frequencies requires a technique and apparatus which are too delicate to serve at the present time as a practical test of the aging of vulcanized rubber. On the other hand, from the viewpoint of research, the dielectric method should furnish valuable data on the way in which oxygen tends to combine with rubber according to the particular conditions of aging. Thus, it has been found in aging tests of three different types of vulcanizates containing no protective agent that there is an increase of polarity, which is in some cases great, an increase of the dielectric viscosity, and a broad distribution of polar groups, formed by oxidation, between the different types of structures. The dielectric absorption leads in particular to the same classification of vulcanizates as do the classic methods of measuring oxidizability and decrease of tensile strength. Finally, in addition, measurement of the dielectric absorption makes possible the estimation at a high level of sensitivity of the degree of polarity of oxidation products.

Modification and Dielectric Properties of Polyisoprene

1983 ◽  
Vol 56 (4) ◽  
pp. 718-725
Author(s):  
J. Honskus
Keyword(s):  
Dielectric Properties ◽  
Chemical Analyses ◽  
Dielectric Measurements ◽  
Dielectric Method ◽  
Polar Groups ◽  
Good Agreement

Abstract The dielectric method can be used for determination of the polar groups modifying the nonpolar polymers. This method was used for the study of such complicated systems as the sulfur-accelerated vulcanizates. Results of the chemical analyses were compared with the results of dielectric measurements, and very good agreement was obtained.

scholarly journals Recent Advancements in Pyrrole Synthesis

Synthesis ◽  
2021 ◽  
Vol 53 (09) ◽  
pp. 1531-1555
Author(s):  
Satish Chandra Philkhana ◽  
Fatimat O. Badmus ◽  
Isaac C. Dos Reis ◽  
Rendy Kartika
Keyword(s):  
Carbonyl Compounds ◽  
Polar Compounds ◽  
Review Article ◽  
Dicarbonyl Compounds ◽  
Aromatic Heterocycle ◽  
Polar Groups ◽  
Different Types ◽  
Synthetic Reactions

AbstractThis review article features selected examples on the synthesis of functionalized pyrroles that were reported between 2014 and 2019. Pyrrole is an important nitrogen-containing aromatic heterocycle that can be found in numerous compounds of biological and material significance. Given its vast importance, pyrrole continues to be an attractive target for the development of new synthetic reactions. The contents of this article are organized by the starting materials, which can be broadly classified into four different types: substrates bearing π-systems, substrates bearing carbonyl and other polar groups, and substrates bearing heterocyclic motifs. Brief discussions on plausible reaction­ mechanisms for most transformations are also presented.1 Introduction2 From π-Systems2.1 Alkenes2.2 1,6-Dienes2.3 Allenes2.4 Alkynes2.5 Propargylic Groups2.6 Homopropargylic Amines3 From Carbonyl Compounds3.1 Aldehydes3.2 Ketones3.3 Cyanides and Isocyanides3.4 Formamides3.5 β-Enamines3.6 Dicarbonyl Compounds4 From Polar Compounds4.1 Aminols4.2 Diols4.3 Organonitro Compounds5 From Heterocycles5.1 Münchnones5.2 Isoxazoles5.3 Carbohydrates5.4 trans-4-Hydroxy-l-prolines5.5 Pyrrolines6 Summary

Improving dielectric properties and thermal conductivity of polymer composites with CaCu3Ti4O12 and β-SiC hybrid fillers

2015 ◽  
Vol 08 (03) ◽  
pp. 1540011 ◽  
Author(s):  
Xin Ouyang ◽  
Peng Cao ◽  
Weijun Zhang ◽  
Zhaohui Huang ◽  
Wei Gao
Keyword(s):  
Thermal Conductivity ◽  
Dielectric Constant ◽  
Dielectric Properties ◽  
Dielectric Response ◽  
Interfacial Polarization ◽  
Melt Blending ◽  
Hybrid Fillers ◽  
Different Types ◽  
Thermally Conductive ◽  
Sic Whiskers

In this paper, we report a series of homogeneous polymeric composites with enhanced dielectric properties and thermal conductivity. The composites were constituted of polyvinylidene fluorides (PVDFs) matrix and CaCu 3 Ti 4 O 12 (CCTO) monolithic or CCTO/β- SiC hybrid fillers, and prepared by simple melt blending and hot moulding technique. The influence of different types of fillers and their composition on the dielectric response and thermal conductivity of the obtained composites was studied. Results show that hybrid loading is preferred and a reasonable combination of thermal conductivity (0.80 W⋅m-1⋅K-1), dielectric constant (∼50) and dielectric loss (∼0.07) at 103 Hz was achieved in the PVDF composite containing 40 vol.% CCTO and 10 vol.% β- SiC . The strong dipolar and interfacial polarization derived from the fillers are responsible for the enhancement of the dielectric constant, while the formation of thermally conductive networks/chains by β- SiC whiskers contributes to the improved thermal conductivity.

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