Transport properties of polymer solutions. A comparative approach

A variety of transport properties have been measured for solutions of the water soluble polymer poly(ethylene oxide)(PEO) with molecular weights ranging from 200 to 14,000, and volume fractions ranging from 0-80%. The transport properties are thermal conductivity, electrical conductivity at audio frequencies (in solutions containing dilute electrolyte), and water self-diffusion. These data, together with dielectric relaxation data previously reported, are amenable to analysis by the same mixture theory. The ionic conductivity and water self-diffusion coefficient, but not the thermal conductivity, are substantially smaller than predicted by the Maxwell and Hanai mixture relations, calculated using the known transport properties of pure liquid water. A 25% (by volume) solution of PEO exhibits an average dielectric relaxation frequency of the suspending water of one half that of pure water, with clear evidence of a distribution of relaxation times present. The limits of the cumulative distribution of dielectric relaxation times that are consistent with the data are obtained using a linear programming technique. The application of simple mixture theory, under appropriate limiting conditions, yields hydration values for the more dilute polymer solutions that are somewhat larger than values obtained from thermodynamic measurements.     

Theoretical study on the stability,electronic, mechanical,vibrational and thermodynamic properties of rare-earth intermetallic compound Rh3Ce

The structural, stability, electronic, mechanical, vibrational and thermodynamic properties of rare-earth intermetallic compound Rh₃Ce have been explored systematically by using first-principle calculations. The evaluation of the equilibrium lattice parameters were obtained firstly. Remarkably, the result of calculated unit cell volume, derived by the total energies as a function of volume, is consistent with other results. Next, the values of cohesive energy (E_c), formation enthalpy (ΔH) have verified that Rh₃Ce is a stable compound. In addition, the band structure and the total density of states indicate a metallic behaviour. Furthermore, the Mulliken charges were calculated to understand the bonding in Rh₃Ce compound. Otherwise, the elastic constants(C_ij) as well as other modulus were also calculated to evaluated the mechanical properties of Rh₃Ce. Phonon dispersion curves for Rh₃Ce were depicted to access the vibrational properties. Finally, the thermodynamic properties of Rh₃Ce were summarised range from 0 to 60?GPa, 0 to 1800?K, respectively. We also pointed out that the thermal expansion(α), heat capacity(C_v), entropy(S), Debye temperature(Θ) and Güneisen parameter (γ) change under pressure and temperature.     

Enhancement of Thermoelectric Figure of Merit by the Insertion of MgTe Nanostructures in p‐type PbTe Doped with Na2Te

The thermoelectric properties of crystalline melt‐grown ingots of p‐type PbTe–xMgTe (x = 1–3 mol%) doped with Na₂Te (1–2 mol%) were investigated over the temperature range of 300 K to 810 K. While the powder X‐ray diffraction patterns show that all samples crystallize in the NaCl‐type structure with no MgTe or other phases present, transmission electron microscopy reveals ubiquitous MgTe nanoprecipitates in the PbTe. The very small amounts of MgTe in PbTe have only a small effect on the electrical transport properties of the system, while they have a large effect on thermal transport significantly reducing the lattice thermal conductivity. A ZT of 1.6 at 780 K is achieved for the PbTe containing 2% MgTe doped with 2% Na₂Te.     

Effect of Dislocation Arrays at Grain Boundaries on Electronic Transport Properties of Bismuth Antimony Telluride: Unified Strategy for High Thermoelectric Performance

Taming electronic and thermal transport properties is the ultimate goal in the quest to achieve unprecedentedly high performance in thermoelectric (TE) materials. Most state‐of‐the‐art TE materials are inherently narrow bandgap semiconductors, which have an inevitable contribution from minority carriers, concurrently decreasing Seebeck coefficient and increasing thermal conductivity. Nevertheless, the restraint control of minority carrier transport is seldom considered as a key element to enhance the TE figure of merit (zT). Herein, it is verified that the localized dislocation arrays at grain boundaries enable the suppression of minority carrier contribution to electronic transport properties, resulting in an increase of the Seebeck coefficient and the carrier mobility in bismuth antimony tellurides. It is also suggested that the suppression of minority carriers via the generation of dislocation arrays at grain boundaries is an effective and noninvasive strategy to optimize overall electronic transport properties without sacrificing predominant characteristics of majority carriers in TE materials.     

The role of interphase nitrogen transport in the dynamic measurement of the overall volumetric mass transfer cefficient in air-sparged systems

It has been shown both theoretically and experimentally that interphase nitrogen transport may have a significant influence on the rate of interphase oxygen transport, and thereby also on the value of the volumetric mass transfer coefficient of oxygen, k_la, determined in mechanically agitated bubble fermentors using the variants of dynamic method presented in the literature. The experiments were carried out in 1M KCI solution at five stirrer frequencies and two gas inlet levels. The gas interchanges were performed either without interrupting the aeration and agitation of the charge (A) or with the aeration and agitation of the charge turned on at the same time (B). The applied variants of the interchange were N₂→ O₂→, O₂→ N₂, N₂→ air, air→ N₂, O→ O₂, and O→ air. In the two last variants the oxygen dissolved in the charge was removed by reacting with sulfite ions. The k_la values calculated by allowing for the nitrogen transport for procedure A were approximately equal to the values obtained by disregarding the nitrogen transport, whereas those for procedure B were higher (up to 40%), than the values obtained disregarding the nitrogen transport.     

Phonon and thermoelectric properties of single- and double-walled carbon nanotubes from first principles

The phonon and thermal properties of different single- ((n,0) (n = 7,8,9,10,14,15)) and double-walled carbon nanotubes ((7, 0) @ (14, 0), (8, 0) @ (14, 0), (9, 0) @ (15, 0) and (10, 0) @ (15, 0),) were calculated using the combination of density functional theory and non-equilibrium Green’s function methods. It was found that the Seebeck and Peltier coefficients for some of the single- and multi-walled carbon nanotubes have negative values. Moreover, in sharp contrast to low ?T, the higher thermoelectric figure of merit is anticipated at the higher temperature. The effect of the atoms number per unit cell on the phonons energies outweighs the effect of the vacuum and the size of the tubes for DWCNTs. All in all, the electron–phonon coupling generates the roughly plethora of thermoelectric coefficients and thermal conductance.     

Frictional properties of multisubunit structures

The translational drag, rotational drag, and intrinsic viscosity of spherical multisubunit structures have been calculated analytically using the Felderhof–Deutch theory of polymer frictional properties. The structures considered were hollow shells, spheres with uniform subunit density, and spheres covered with a subunit layer of different density. Changes in the transport coefficients resulting from the random removal of subunits and from the variation of subunit size are calculated. For the case of the shell, the results agree with the numerical computations of Bloomfield, Dalton, and Van Holde [Biopolymers 5 , 135, 149 (1967)].     

Transport properties of oligomeric subunit structures

The translational friction coefficients, rotational friction coefficient, and intrinsic viscosity of rigid regular structures composed of up to eight identical spherical subunits have been accurately calculated. The aim of this calculation is to interpret the hydrodynamic properties of oligomeric subunit proteins. To avoid the well-known failure of the theory in the evaluation of rotational coefficients and intrinsic viscosities, each subunit is hydrodynamically modeled as a polyhedral array of smaller spheres. The analysis of several alternatives suggests that a cubic array is the best choice. The reliability of this strategy is checked by comparison of the calculated values for all the transport properties of a sphere and the translational friction coefficients of a dimer with their exact values. Finally, the hydrodynamic properties of a number of subunit structures with varying number of subunits and different geometries are tabulated.     

Analysis of the conformation and thermal stability of the high-affinity IgE Fc receptor β chain polymorphic proteins*

The high-affinity IgE Fc receptor (FcεRI) β chain acts as a signal amplifier through the immunoreceptor tyrosine-based activation motif in its C-terminal intracellular region. Polymorphisms in FcεRI β have been linked to atopy, asthma, and allergies. We investigated the secondary structure, conformation, and thermal stability of FcεRI β polymorphic (β-L172I, β-L174V, and β-E228G) proteins. Polymorphisms did not affect the secondary structure and conformation of FcεRI β. However, we calculated Gibbs free energy of unfolding (ΔG_unf) and significant differences were observed in ΔG_unf values between the wild-type FcεRI β (β-WT) and β-E228G. These results suggested that β-E228G affected the thermal stability of FcεRI β. The role of β-E228G in biological functions and its involvement in allergic reactions have not yet been elucidated in detail; therefore, differences in the thermal stability of β-E228G may affect the function of FcεRI β.     

Low Electron Scattering Potentials in High Performance Mg2Si0.45Sn0.55 Based Thermoelectric Solid Solutions with Band Convergence

Understanding the electron and phonon transport characteristics is crucial for designing and developing high performance thermoelectric materials. Weak scattering effects on charge carriers, characterized by deformation potential and alloy scattering potential, are favorable for thermoelectric solid solutions to enable high carrier mobility and thereby promising thermoelectric performance. Mg₂(Si,Sn) solid solutions have attracted much attention due to their low cost and environmental compatibility. Usually, their high thermoelectric performance with ZT ～ 1 is ascribed to the band convergence and reduced lattice thermal conductivity caused by alloying. In this work, both a low deformation potential Ξ = 13 eV and a low alloy scattering potential U = 0.7 eV are found for the thermoelectric alloys by characterizing and modeling of thermoelectric transport properties. The band convergence is also verified by the increased density‐of‐states effective mass. It is proposed that, in addition to band convergence and reduced lattice thermal conductivity, the low deformation potential and alloy scattering potential are additional intrinsic features that contribute to the high thermoelectric performance of the solid solutions.     

Understanding the thermal properties of amorphous solids using machine-learning-based interatomic potentials

Abstract

Understanding the thermal properties of disordered systems is of fundamental importance for condensed matter physics - and for practical applications as well. While quantities such as the thermal conductivity are usually well characterised experimentally, their microscopic origin is often largely unknown - hence the pressing need for molecular simulations. However, the time and length scales involved with thermal transport phenomena are typically well beyond the reach of ab initio calculations. On the other hand, many amorphous materials are characterised by a complex structure, which prevents the construction of classical interatomic potentials. One way to get past this deadlock is to harness machine-learning (ML) algorithms to build interatomic potentials: these can be nearly as computationally efficient as classical force fields while retaining much of the accuracy of first-principles calculations. Here, we discuss neural network potentials (NNPs) and Gaussian approximation potentials (GAPs), two popular ML frameworks. We review the work that has been devoted to investigate, via NNPs, the thermal properties of phase-change materials, systems widely used in non-volatile memories. In addition, we present recent results on the vibrational properties of amorphous carbon, studied via GAPs. In light of these results, we argue that ML-based potentials are among the best options available to further our understanding of the vibrational and thermal properties of complex amorphous solids.     

Thermo-mechanical properties of cubic titanium nitride

The equilibrium structure, elastic constants C_ij and thermodynamic functions of cubic titanium nitride (TiN) were calculated within the temperature range of 0–3100 K and under a pressure range 0–60 GPa. Properties were computed using the generalised gradient approximations (GGA) exchange-correlation functional. Calculated mechanical properties (Elastic constants, Young’s modulus and shear modulus) and phonon spectra of TiN obtained via robust DFT-QHA algorithm, were generally in a good agreement with available experimental and theoretical analogous values. In particular, a well-examined quasi-harmonic approximation method implemented in the Gibbs2 code is utilised herein to provide accurate estimation of thermal expansion coefficients, entropies, heat capacity values (at different combinations of temperature/volume/pressure) and Debye’s temperature. Parameters calculated herein shall be useful to elucidate the superior performance of TiN at harsh operational conditions encompassing elevated temperatures and pressures pertinent to cutting machineries and surface coatings.     

Theoretical studies on the conformation of saccharides. VIII. Solvent effect on the stability of β-cellobiose conformers

The conformational equilibria of five β-cellobiose conformers have been studied theoretically in 10 solvents. The stability of the conformers in dilute solution has been compared by using the method that has already been tested for 2-methoxytetrahydropyran, β-maltose, and D -glucose. The solvation energy consists of electrostatic, dispersion, and cavity terms which have been determined from the properties of the solute calculated by the PCILO quantum-chemical method and physicochemical properties of the solvents. The calculated abundance of conformers depends on the solvent (e.g., in dioxane C1:C2:C3:C4:C5 = 60.0:34.1:2.9:2.0:1.0; in dimethylsulfoxide, 75.5:22.1:1.8:0.5:0.2; and in water, 82.2:16.2:1.3:0.2:0.1). The results obtained indicate that the preponderant conformer in the aqueous solution is similar to the one adopted by β-cellobiose in the crystalline form. The role of individual contributions to the solvation energy have been analyzed. Based on the determined abundance of conformers, averaged residual optical activity and nmr parameters have been calculated and compared with observable properties. The marked differences observed between solvent-induced conformational changes for β-cellobiose and β-maltose have been discussed from the viewpoint of the solubility of the cellulose.     

Controlling Metallurgical Phase Separation Reactions of the Ge0.87Pb0.13Te Alloy for High Thermoelectric Performance

We demonstrate the potential of metallurgical controlling of the phase separation reaction, by means of spark plasma sintering consolidation and subsequently controlled heat treatments sequence, for enhancement the thermoelectric properties of the p‐type Ge_0.87Pb_0.13Te composition. Very high ZTs of up to ～2, attributed to the nucleation of sub‐micron phase separation domains and to comparable sized twinning and dislocation networks features, were observed. Based on the experimentally measured transport properties, combined with the previously reported phase separated n‐type (Pb_0.95Sn_0.05Te)_0.92(PbS)_0.08 composition, a maximal efficiency value of ～11.5% was theoretically calculated. These ZT and efficiency values are among the highest reported for single composition non‐segmented bulk material legs.     

Inbreeding and endogamy in Tatarstan

The random inbreeding (F _st) and local inbreeding (a) values have been calculated for populations of the district and rural municipality ranks of 16 and 13 raions (administrative districts) of Tatarstan, Russia, respectively. The correlations between all inbreeding values are positive and vary from 0.38 to 0.80. The endogamy index has been calculated for populations of the district rank; it varies from 0.45 in Pestrechinskii raion to 0.74 in Aktanyshskii raion. Cartographic extrapolation of the endogamy indices has been performed.     

Grain Boundary Scattering of Charge Transport in n‐Type (Hf,Zr)CoSb Half‐Heusler Thermoelectric Materials

High thermoelectric figure of merit zT of ≈1.0 has been reported in both n‐ and p‐type (Hf,Zr)CoSb‐based half‐Heusler compounds, and further improvement of thermoelectric performance relies on the insightful understanding of electron and phonon transport mechanisms. In this work, the thermoelectric transport features are analyzed for (Hf_0.3Zr_0.7)_1?xNb_xCoSb (x = 0.02–0.3) with a wide range of carrier concentration. It is found that, although both temperature and energy dependencies of charge transport resemble ionized impurity scattering, the grain boundary scattering is the dominant scattering mechanism near room temperature. With increasing carrier concentration and grain size, the influence of the grain boundary scattering on electron transport weakens. The dominant scattering mechanism changes from grain boundary scattering to acoustic phonon scattering as temperature rises. The lattice thermal conductivity decreases with increasing Nb doping content due to the increased strain field fluctuations. These results provide an in‐depth understanding of the transport mechanisms and guidance for further optimizing thermoelectric properties of half‐Heusler alloys and other thermoelectric systems.     

Substituted azomethine-zinc complexes: Thermal stability, photophysical, electrochemical and electron transport properties

A series of zinc complexes with salicylidene-aniline and its derivatives as ligands have been designed and synthesized for electron transport in organic light-emitting diodes (OLEDs). A systematic study on their thermal, photophysical, electrochemical and electron transport properties has been carried out and demonstrated that the substitution of −CH₃, −OCH₃, −CN and −N(CH₃)₂ on aniline ring of ligands can finely tune the properties of the corresponding zinc complexes. The density functional theory calculations of location and distribution of the frontier molecular orbital states unveiled the relationships between the substituents and the photophysical and electrochemical properties of these complexes. OLEDs with bis(salicylidene-p-methylaniline)zinc(II) (Zn(sama)₂) as the electron transport layer exhibited high current efficiency, indicating its great potential as a useful electron transport material for OLEDs.     

The phloem mobility of glucosinolates

The transport properties of glucosinolates within Brassica napus are of interest as identification of the mechanism of transport could lead to lower levels being obtained in specific tissues such as the seeds. The phloem mobility of ³⁵S-gluconapin (but-3-enylglucosinolate) and ³⁵S-desulphogluconapin in oilseed rape plants has been inferred from tissue distribution patterns, as well as from observed coincident phloem mobility of ³H-gluconapin and ¹⁴C-sucrose. The measured relative phloem mobilities for sinigrin (2-propenylglucosinolate), ³H-gluconapin, ³⁵S-desulphogluconapin, ³⁵S-desulphosinigrin, ¹⁴C-tryptophan, ³H-AIB (-aminoisobutyric acid), and literature values for a reduced ³H-oligogalacutonide elicitor (degree of polymerization 6) and ¹⁴C-IAA (indolylacetic acid), have been compared with the predicted values obtained using the Kleier model for phloem mobility of xenobiotics. All the above compounds show phloem systemicity, demonstrated using the Ricinus assay, as predicted by the model. Log Kow (octanol-water partition coefficient) values for glucosinolates and desulphoglucosinolates measured at pH 4 and pH 7, and the effect of pH on uptake by oilseed rape embryos are provided as evidence against a weak acid trap mechanism acting in either the phloem mobility or the accumulation of glucosinolates in oilseed rape embryos. The phloem mobility of glucosinolates is explained by the intermediate permeability hypothesis. In conclusion, it would appear that glucosinolates like other groups of endogenous compounds have physicochemical properties allowing phloem mobility as predicted by the Kleier model.Keywords: Brassica napus, Ricinus communis, phloem mobility, glucosinolates, Kleier model.      

Transport kinetics of maltotriose in strains ofSaccharomyces

Summary Maltotriose transport was studied in two brewer's yeast strains, an ale strain 3001 and a lager strain 3021, using laboratory-synthesized¹⁴C-maltotriose. The maltotriose transport systems preferred a lower pH (pH 4.3) to a higher pH (pH 6.6). Two maltotriose transport affinity systems have been indentified. The high affinity system hasK _m values of 1.3 mM for strain 3021 and 1.4 mM for strain 3001. The low affinity competitively inhibited by maltose and glucose withK _i values of 58 mM and 177 mM. respectively, for strain 3021, and 55 mM and 147 mM, respectively, for strain 3001. Cells grown in maltotriose and maltose had higher maltotriose and maltose transport rates, and cells grown in glucose had lower maltortriose and maltose transport rates. Early-logarithmic phase cells transported glucose faster than either maltose or maltotriose. Cells harvested later in the growth phase had increased maltotriose and maltose transport activity. Neither strain exhibited significant differences with respect to maltose and maltotriose transport activity.