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Structure and Properties of Polymer Matrix
Published in Noureddine Ramdani, Polymer and Ceramic Composite Materials, 2019
A good design of polymeric molecular structures can result in improved barrier properties. However, generally the property, like polarity, can produce a good gas barrier, while provoking a poor water barrier. Highly polar polymers containing a huge amount of hydroxyl groups (poly(vinyl alcohol) or cellophane) are excellent gas barriers, but they are considered the poorest water barriers. Moreover, they become poor gas barriers as they plasticize using water. In contrast, the nonpolar hydrocarbon polymers, such as polyethylene, show good water barrier properties but poor gas barrier properties. To achieve good barrier properties polymer must have: Appropriate degree of polarity comparable to that of the nitrile radical, the chlorine, fluorine, acrylic, or ester group;High chain stiffness;Inertness;Close chain-to-chain packing by symmetry, order, crystallinity, or orientation;Good bonding or attraction between chains;High Tg.
Photonic Quasicrystals: Basics and Examples
Published in Filippo Capolino, Theory and Phenomena of Metamaterials, 2017
Alessandro Della Villa, Vincenzo Galdi, Filippo Capolino, Stefan Enoch, Gérard Tayeb
For the PQC geometries in Figure 27.5, we carried out a comprehensive parametric study of the radiativity response, for several combinations of the rods’ permittivity and filling factor values and at various positions r0, aimed at gaining some insights into the underlying aperiodic-order-induced bandgap phenomena. Some representative results, extracted from Ref. [99], are shown in Figure 27.6, for ∼ 7% filling factor and two values of the relative permittivity єr = 6, 12. In these plots, the radiativity in Equation 27.3 (computed at the center of the structure, r0 = 0) is displayed as a function of the normalized frequency a/λ0, with a denoting the period of the reference PC in Figure 27.5a and λ0 denoting the free-space wavelength. Bandgaps, identified by deep minima of the radiativity, can be observed for both permittivity values, though considerably more pronounced for the highercontrast case (єr = 12). As compared with the PC reference case, the PQCs tend to exhibit a generally richer bandgap structure, which typically entails a main bandgap (moderately deeper than the periodic counterpart) plus certain secondary bandgaps at lower and higher frequencies. Moreover, as the symmetry order is increased, several in-band peaks (attributable to localized modes) tend to appear (cf. Figure 27.6d and f).
Polarized Nano-Optics
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
where the parameter Sn denotes symmetry order contributions of order n in the molecular distributions and the angle ρn refers to the orientations of these symmetry order in the sample plane. The Sn coefficients allow to identify specific contributions: S0 determines the isotropic contribution of (ϕ), S2 its anisotropy, and higher orders Sn define more precisely the shape of this function. Each of the symmetry order Sn has a specific orientation ρn, allowing to define functions of very general shape, including those that do not possess a cylindrical symmetry axis (Ferrand et al., 2014).
The characterization of electronic defect states of single and double carbon vacancies in graphene sheets using molecular density functional theory
Published in Molecular Physics, 2019
Max Pinheiro, Daniely V. V. Cardoso, Adélia J. A. Aquino, Francisco B. C. Machado, Hans Lischka
For the relaxed structures, the results obtained with HSE06 and CAM-B3LYP (Table S8) present to some extent a different picture as compared to the B3LYP results. For circumpyrene-1C, the 3B1 ground state and the 3A2 state, which represent charge transfer (CT) states arising from delocalised π orbitals to the σ orbital of the local defect structure, were almost degenerate at B3LYP level, differing by 0.07 eV. However, HSE06 and CAM-B3LYP predict 3A2 as the ground state whereas the 3B1 state lies above by 0.137 and 0.010 eV. The closed shell 1A1 state, which was 0.767 eV above the ground state at B3LYP is around 1.5 eV above with HSE06 and CAM-B3LYP. For the 7a,7z-periacene-1C, B3LYP and the range-separated functionals agree in predicting a triplet multiplicity for the ground state, although they differ with respect to the state symmetries and excitation energies. While 3B1 is found to be the ground state at the B3LYP level followed by the four-fold open shell state 3A2 state 0.09 eV higher. This symmetry order is reversed using HSE06 and CAM-B3LYP with the 3B1 state lying above by 0.411 and 0.366 eV, respectively. The closed shell 1A1 state, which was 0.855 eV above the ground state with B3LYP, is much higher now above the ground state at HSE06 and CAM-B3LYP levels (2.131 and 3.680 eV, respectively).
1,3-Dimethyl-2-phenyl-1,3-diazaphospholidine-2-oxide as ligand for the preparation of luminescent lanthanide complexes
Published in Journal of Coordination Chemistry, 2019
Marco Bortoluzzi, Alberto Gobbo
Absorption and photoluminescence data of the β-diketonate complexes are summarized in Table 2. As observable in Figure 2, dichloromethane solutions of the compounds are characterized by strong absorptions in the near-UV range. Solid-state photoluminescence measurements showed that the excitation of the coordinated ligands with wavelengths below 480 nm causes the emission from the Eu(III) center (Figure 2). Direct excitation of Eu(III) is also present in the PLE spectra, corresponding to the 5D2←7F0 transition centered at 464 nm [73]. The PL spectra display only the typical 5D0→7FJ bands, the most intense occurring for J = 2. The 5D0→7F2/5D0→7F1 intensity ratio ranges from 15.8 (β-dike = dbm) to 19.2 (β-dike = tta) and the 5D0→7F1 transition is separated into three peaks because of the Stark effect. These data suggest low symmetry of the first coordination sphere, with 2 the maximum possible rotational symmetry order, in agreement with the results of DFT calculations. The occurrence of only one 5D0→7F0 transition supports the presence of only one Eu(III) emitting center, even if such information is not conclusive [73].
The phase diagram and melting scenarios of two-dimensional Hertzian spheres
Published in Molecular Physics, 2018
Yu. D. Fomin, E. A. Gaiduk, E. N. Tsiok, V. N. Ryzhov
An important shortcoming of the order parameters introduced above is that they are applicable to a single crystal structure only. That is why if one finds a novel crystal structure with different symmetry order parameters can be zero in this structure. Therefore, it can be difficult to find out the symmetry of the structure using order parameters only. This problem can be solved by calculating diffraction patterns. The diffraction patterns are the intensity maps of the static structure factor: