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Polymer Crystallization
Published in Anil Kumar, Rakesh K. Gupta, Fundamentals of Polymer Engineering, 2018
Recall that the refractive index is a measure of the velocity of light in the medium and is related to the polarizability of the molecular chains in the sample. One way to determine the refractive indices parallel and perpendicular to the fiber axis is to immerse the fiber in oil of known refractive index and to observe the combination, using a polarizing microscope, with the plane of the polarized light parallel to the fiber, and then perpendicular to the fiber, as sketched in Figure 11.26. When both the sample and the immersion oil have the same refractive index, the fiber is no longer visible.
Electricity and Electronic Devices
Published in David M. Scott, Industrial Process Sensors, 2018
Capacitors store charge in two electrodes (one positive, one negative) that are separated by a thin dielectric material. A dielectric is a nonconducting material that is polarizable, which means that bound charges within it can rearrange themselves to minimize the electric field. The dielectric constant is a material property that is closely related to the polarizability. For a simple parallel plate capacitor, the voltage drop across the electrodes (and therefore across the capacitor) is equal to the electric field [V/m] times the thickness of the dielectric layer m. By choosing a material with a higher dielectric constant, the electric field and therefore VC are both minimized for a given amount of charge. From equation 5.20 it should be evident that the capacitance of such a device is greater than that of the original capacitor. In general, the capacitance for a given electrode geometry is proportional to the dielectric constant.
Thermal analysis
Published in D. Campbell, R.A. Pethrick, J.R. White, Polymer Characterization, 2017
D. Campbell, R.A. Pethrick, J.R. White
When a polar polymer is placed in an electric field the permanent electric dipoles will attempt to align with the field direction. Their realignment is retarded by the neighbouring elements of the polymer. As the temperature is increased so various types of dipoles will become active and this gives rise to changes in the polarizability of the material. If the polymer is below Tg realignment of the backbone is not possible and it is only the conformational changes of the side chain or short elements of the backbone which are possible. If an alternating field is applied the dipoles will be encouraged to move in opposite directions on alternate half cycles. If the temperature is too low or the frequency of the field too high it is impossible for them to follow. If the temperature is high, however, the dipoles can realign repeatedly and this causes energy to be withdrawn from the driving field and appears as heat. The polarization lags behind the energizing electric field and the angle, δ, and the corresponding tan δ values have a similar significance to that described for DMTA (Section 12.5). Analogous to the mechanical case, the properties of the material are described in terms of a complex dielectric permittivity (ɛ*), which contains a storage component (ɛ′) and a loss component (ɛ″):
Study on molecular structure, Spectral investigations, NBO, NLO, Hirshfeld surface analysis and Homo-Lumo energy of silver complex of 4-Amino-N-(2,6-dimethoxypyrimidin-4-yl)benzenesulfonamide
Published in Inorganic and Nano-Metal Chemistry, 2018
Rahul P. Dubey, Urmila H. Patel, Bharatkumar D. Patel
Additionally, it is also planned to illuminate theoretical determination of the optimized molecular geometries (Ag-SDM). Here we have presented a comprehensive investigation on the molecular properties of Ag-SDM by DFT studies. Optimized theoretical data of bond lengths and bond angles are compared with those of experimental (X-ray) data. NBO analysis is study in order to have a measure of an intramolecular delocalization of hyper-conjugation. The molecular properties like NLO, molecular electrostatic potential surface (MEPs), and Homo-Lumo energies have been calculated to get a better understanding of the properties of the title molecule. The binding energy between two molecules is proportional to their value of static polarizability. A high polarizability value of molecule explains that this molecule may have high binding energy with the protein receptor.[12–13] MEP surface is very much useful to identify the reactive sites of the proposed molecule. Further, Hirshfeld surfaces and consequently the fingerprint analysis have been performed to study contribution of various interactions towards the crystal packing.[14]
Dielectric characterisation of rock aggregates with different grain size distributions
Published in Road Materials and Pavement Design, 2023
Benhui Fan, Frédéric Bosc, Benjamin Smaniotto, Zhong-Sen Li, Jinbo Bai, Cyrille Fauchard
As mentioned before, ten discs of LA were tested by an impedance analyzer. The frequency-dependent dielectric permittivities are presented in Figure 5. As shown in Figure 5, the dielectric properties of the 10 LA discs are quite dispersive in the tested frequency range. It is known that the dielectric properties of a material are related to the polarizability (α) that depends on the charge displacement in a material. Each polarisation mechanism describes the charge separation at different length scales: as the frequency increases, the dominant mechanism is as follows: (i) interfacial polarisation from 10−2–103 Hz (also known as Maxwell–Wagner or space charge polarisation), (ii) dipolar polarisation from 104–108 Hz (also known as orientational polarisation), (iii) atomic/ionic polarisation and electronic polarisation for frequencies larger than 109 Hz, respectively (Kasap, 2007). In this test, the frequency range is from 1 Hz to 1 MHz where the interfacial and the dipolar polarizations are the main contributions. These two polarizations are strongly related to the mineralogical composition and the microstructure of a material. As shown by CT scanning, the aggregates in our study have different densities, and possibly various crystalline structures and orientations, which causes the variation in the dipolar polarisation and the relaxation of space charges in the interfacial area. Thus, at low frequencies, a large variety in the dielectric properties of the 10 samples is observed, especially when the frequency is lower than 1000 Hz. However, the variety in dielectric permittivity is reduced when the frequency increases over 105 Hz since the relaxations cannot catch up with the high frequency. The frequency-dependent characteristic allows us to use the dielectric relaxation models to derive the dielectric constant at high frequencies.
A scale of absolute hardness based on the conjoint action of other properties
Published in Molecular Physics, 2022
Swetha Sara Sabu, S. Jane Anto Simplica, Hiteshi Tandon, Tanmoy Chakraborty
Polarizability is understood as the distortion in electron cloud due to applied electric field. When outermost electrons are held less strongly, they can be easily distorted. When the radius of an atom is small, effective nuclear charge holds outermost electrons tightly, making it less polarizable. Decrease in polarizability may tend to increase hardness. Szarek and Grochala [20] related atomic radius to polarizability (α) and hardness (η) as: