Dynamic Conductivity Research Articles

Electrically Conductive Silicone-Based Nanocomposites Incorporated with Carbon Nanotubes and Silver Nanowires for Stretchable Electrodes.

Stretchable electrode materials have attracted great attention as next-generation electronic materials because of their ability to maintain intrinsic properties with rare damage when undergoing repetitive deformations, such as folding, twisting, and stretching. In this study, an electrically conductive PDMS nanocomposite was manufactured by combining the hybrid nanofillers of carbon nanotubes (CNTs) and silver nanowires (AgNWs). The amphiphilic isopropyl alcohol molecules temporarily adhered simultaneously to the hydrophobic CNT and hydrophilic AgNW surfaces, thereby improving the dispersity. As the CNT/AgNW ratio (wt %/wt %) decreased under the constant nanofiller content, the tensile modulus decreased and the elongation at break increased owing to the poor interaction between the AgNWs and matrix. The shear storage moduli of all nanocomposites were higher than the loss moduli, indicating the elastic behavior with a cross-linked network. The electrical conductivities of the nanocomposite containing the hybrid nanofillers were superior to those of the nanocomposite containing either CNT or AgNW at the same filler content (4 wt %). The hybrid nanofillers were rearranged and deformed by 5000 cyclic strain tests, relaxing the PDMS matrix chain and weakening the interfacial bonding. However, the elastic behavior was maintained. The dynamic electrical conductivities gradually increased under the cyclic strain tests due to the rearrangement and tunneling effect of the nanofillers. The highest dynamic electrical conductivity (10 S/m) was obtained for the nanocomposite consisting of 2 wt % of CNTs and 2 wt % of AgNWs.

Physical properties of deep eutectic solvents based on p-toluene sulfonic acid and employment as catalyst

This work studied the physical properties of three deep eutectic solvents (DESs) and their catalytic activity in the esterification of palmitic acid and ethanol. Three types of deep eutectic solvents (DESs) were successfully prepared using p-toluene sulfonic acid monohydrate (PTSA) as hydrogen bond donor (HBD) with dodecyl trimethyl ammonium chloride (DTAC), tetradecyl trimethyl ammonium chloride (TTAC) and octadecyl trimethyl ammonium chloride (OTAC) as hydrogen bond acceptor (HBA). The freezing points of DESs were measured in the range of 50%–80% HBD mole percentage, and the composition of DTAC-PTSA, TTAC-PTSA and OTAC-PTSA at the eutectic point (the lowest freezing points) was determined respectively (DES1, DES2 and DES3). The physical properties (density, refractive index, dynamic viscosity, conductivity and pH value) of DES1∼DES3 were studied respectively in the temperature range of 298.15 K to 343.15 K. The results showed that dynamic viscosity, conductivity, density and refractive index all change approximately regularly with the increase of temperature, while pH value remains almost constant when the temperature exceeds 325 K. The catalytic ability of the three DESs in the esterification reaction of palmitic acid and ethanol was investigated, and DES2 was selected as the catalyst for subsequent experiments. The effects of temperature, acid-ethanol molar ratio, catalyst dosage and reaction time on esterification reaction were further studied, and DES’ recyclability was also tested. The results obtained showed the great potential of DES in catalytic applications.

Dynamic electrical conductivity induced by isothermal crystallization in aluminum hydroxide filled silicone rubber

In this paper, taking aluminum hydroxide (ATH) filled silicone rubber as a model composite, we report the “n-shape” dynamic electrical conductivity during isothermal crystallization in nonconductive particles filled insulating polymers. During the initial crystallization, rapid growth of dominant lamellae blocks the transport path of impurity ions, contributing to the remarkable reduction of conductivity. Addition of ATH fillers could reduce the silicone rubber content and randomness of crystals formation, lessening the amplitude of decreased conductivity. Afterward, the silicone rubber composites further shrink due to the development of subsidiary lamellae. It results in low activation energy of ion migration and thereby enhances conductivity, whose amplitude is positively related to the crystalline phase. Finally, continuous growth of rigid amorphous fraction with reduced chain mobility impedes the ions transport, decreasing the conductivity again. The growth of rigid amorphous fraction is accelerated in silicone rubber with more ATH fillers because of more constraint of ATH on molecular chains. Our findings afford a simple means to manipulate insulation performance of nonconductive particles filled semi-crystalline polymers and provide a guideline for their use in real operation.

Spin transport on the ferromagnetic checkerboard lattice

I study spin transport on the anisotropic ferromagnetic checkerboard lattice with a Dzyaloshinskii -Moriya interaction and an easy-axis anisotropy term. I show that by fine-tuning the parameters, we can get a flat band. The transverse and longitudinal dynamical spin conductivities are calculated using a Kubo formula. The Drude weight was also calculated as a function of temperature. The Drude weight vanishes at T = 0 but is finite for T > 0. A finite Drude weight indicates an ideal conductor, which we refer to as ballistic transport.

Enhanced Dielectric Relaxation in Self-Organized Layers of Polypeptides Coupled to Platinum Nanoparticles: Temperature Dependence and Effect of Bias Voltage

Using alternative current impedance spectroscopy, we investigate the dynamical conductivity of hybrid nanomaterials composed of helical polypeptide layers containing platinum nanoparticles (PtNP). The electrical characteristics of the self-organized poly(γ-benzyl-l-glutamate) (PBGL) in bidimensional lamellar assembly in the presence of Pt nanoparticles are well modeled and described by a single equivalent circuit of parallel resistance and capacitance. The latter are determined using a comparison between the measured and calculated Nyquist plots, which allows extracting the characteristic relaxation time and frequency of the dipolar relaxation process. We found that the relaxation frequency in the PBLG–PtNP hybrid materials is enhanced by 4 orders of magnitudes compared to pure PBLG, which indicates a much faster dielectric relaxation in PBLG–PtNP due to dipole orientation and dipole–dipole interactions. The temperature dependence of the relaxation time is analyzed using Arrhenius plots, from which the activation energy of the relaxation process is found to be around 0.1 eV. Such a value close to the peptide vibration energy of the PBLG indicates a vibration-assisted relaxation process and a polaronic charge transport mechanism. An advantage of the PBLG–PtNP nanocomposite material is that the activation energy can be finely tuned by the PBLG degree of polymerization. Finally, an important outcome of this work is the investigation of the dielectric relaxation process in PBLG–PtNP under applied DC bias. We found that the activation energy decreases with increasing bias voltage for all degrees of polymerization of the PBLG molecule. This effect is interpreted in terms of electric field-induced alignment of the dipoles and of increased mobility of the polaronic charge carriers. The presence of piezoelectricity in the hybrid material gives the possibility to use the DC bias as a simple mean of monitoring the dynamical conductivity involving polaronic states.

Dynamical conductivity of warm dense matter from correlation functions with account for interband transitions

Within the generalized linear response theory, the dynamical conductivity of charged particle systems is obtained from equilibrium correlation functions. Using the force–force correlation function approach, interband transitions in addition to phonon interaction and umklapp processes are taken into account for warm dense matter. For solid-density aluminum and copper plasmas, the results are shown for dynamical collision frequency, dynamical conductivity, and opacity as functions of laser frequency accounting for interband absorption. Calculated opacities for aluminum plasmas are compared with results of first-principles density functional theory–molecular dynamic (DFT-MD) simulations and recent experiments. The problem of underestimating the size of opacities by theoretical models in the vicinity of the L edge is discussed.

Quasiparticle twist dynamics in non-symmorphic materials

Quasiparticle physics underlies our understanding of the microscopic dynamical behaviors of materials that govern a vast array of properties, including structural stability, excited states and interactions, dynamical structure factors, and electron and phonon conductivities. Thus, understanding band structures and quasiparticle interactions is foundational to the study of condensed matter. Here we advance a ‘twist’ dynamical description of quasiparticles (including phonons and Bloch electrons) in non-symmorphic chiral and achiral materials. Such materials often have structural complexity, strong thermal resistance, and efficient thermoelectric performance for waste heat capture and clean refrigeration technologies. The twist dynamics presented here provides a novel perspective of quasiparticle behaviors in such complex materials, in particular highlighting how non-symmorphic symmetries determine band crossings and anti-crossings, topological behaviors, quasiparticle interactions that govern transport, and observables in scattering experiments. We provide specific context via neutron scattering measurements and first-principles calculations of phonons and electrons in chiral tellurium dioxide. Building twist symmetries into the quasiparticle dynamics of non-symmorphic materials offers intuition into quasiparticle behaviors, materials properties, and guides improved experimental designs to probe them. More specifically, insights into the phonon and electron quasiparticle physics presented here will enable materials design strategies to control interactions and transport for enhanced thermoelectric and thermal management applications.

Coexistence of diffusive and ballistic transport in integrable quantum lattice models

We investigate the high-temperature dynamical conductivity $\sigma(\omega)$ in two one-dimensional integrable quantum lattice models: the anisotropic XXZ spin chain and the Hubbard chain. The emphasis is on the metallic regime of both models, where besides the ballistic component, the regular part of conductivity might reveal a diffusive-like transport. To resolve the low-frequency dynamics, we upgrade the microcanonical Lanczos method enabling studies of finite-size systems with up to $L\leq 32$ sites for XXZ spin model with the frequency resolution $\delta \omega \sim 10^{-3} J$. Results for the XXZ chain reveal a fine structure of $\sigma(\omega)$ spectra, which originates from the discontinuous variation of the stiffness, previously found at commensurate values of the anisotropy parameter $\Delta$. Still, we do not find a clear evidence for a diffusive component, at least not for commensurate values of $\Delta$, particularly for $\Delta =0.5$, as well as for $\Delta \to 0$. Similar is the conclusion for the Hubbard model away from half-filling, where the spectra reveal more universal behavior.

Surface modification of silica micro-powder by titanate coupling agent and its utilization in PVC based composite

Surface modification of silica micro-powder (SMP) was performed by using commercially available titanate coupling agent KTTO, and polyvinyl chloride (PVC) based composites were prepared by melting and blending PVC and processing aids with SMP before and after modification as fillers. Through XRD, FT-IR, XPS, SEM characterizations and contact angle test, it is determined that the surface of SMP was chemically modified by KTTO successfully. The dispersity of SMP was improved after the KTTO modification treatment although no change was found in the crystal structure of SMP. Moreover, excellent hydrophobicity was achieved by a layer of organic molecules on the surface of modified silica micro-powder (mSMP). The static and dynamic mechanical properties, heat resistance, thermal conductivity, and thermal stability of pure PVC, SMP/PVC, and mSMP/PVC composites with respect to cross-sectional micromorphology were compared. The results indicate that KTTO modification treatment effectively improved the mechanical properties of mSMP/PVC composites, especially increasing the tensile strength and notched impact strength by 43% and 36%, respectively. A significant enhancement of the interfacial bonding between the mSMP filler and PVC matrix was also identified. Furthermore, the thermal conductivity and thermal stability of mSMP/PVC composite were improved by the KTTO modification. The mSMP/PVC composite has a potential application in plates and profiles for construction and buildings.

Comparison of optical response from DFT random phase approximation and a low-energy effective model: Strained phosphorene

The engineering of the optical response of materials is a paradigm that demands microscopic-level accuracy and reliable predictive theoretical tools. Here we compare and contrast the dispersive permittivity tensor, using both a low-energy effective model and density functional theory (DFT). As a representative material, phosphorene subject to strain is considered. Employing a low-energy model Hamiltonian with a Green's function current-current correlation function, we compute the dynamical optical conductivity and its associated permittivity tensor. For the DFT approach, first-principles calculations make use of the first-order random phase approximation. Our results reveal that although the two models are generally in agreement within the low-strain and low-frequency regime, the intricate features associated with the fundamental physical properties of the system and optoelectronics devices implementation such as band gap, Drude absorption response, vanishing real part, absorptivity, and sign of permittivity over the frequency range show significant discrepancies. Our results suggest that the random phase approximation employed in widely used DFT packages should be revisited and improved to be able to predict these fundamental electronic characteristics of a given material with confidence. Furthermore, employing the permittivity results from both models, we uncover the pivotal role that phosphorene can play in optoelectronics devices to facilitate highly programable perfect absorption of electromagnetic waves by manipulating the chemical potential and exerting strain and illustrate how reliable predictions for the dielectric response of a given material are crucial to precise device design.

Исследование свойств смесей дизельного топлива с углеродными нанотрубками и характеристик его распыливания

The fuel economy and exhaust emissions of diesel engines can be improved by adding carbon nanotubes to petroleum diesel fuel. Carbon nanotubes, used as a promising nanoscale additive for diesel fuel, have high thermal conductivity and a large surface area to volume ratio. The thermophysical properties of these fuels, which depend on the composition of the mixtures, are analyzed in this study. Findings of research show that carbon nanotubes added to diesel fuel have little effect on its dynamic viscosity and thermal conductivity. By means of numerical models, we simulated the process of atomization and evaporation of diesel fuel with the different carbon nanotubes content in a constant volume combustion chamber. The accuracy of the calculations is confirmed by the good agreement between the calculated and experimental data. Simulation of mixture atomization showed that the jet length linearly depends on the carbon nanotubes content in diesel fuel. The more carbon nanotubes are in the mixture, the smaller the droplet Sauter mean diameter and the angle of the jet cone opening are. The presence of carbon nanotubes in diesel fuel insignificantly affects the fuel vapor content in it.

Using electrochemical impendence to characterize thermal performance of working lubricants

The thermal performance of a lubricant is important for electric-mechanical systems such as electric vehicles. To date, understanding of the dynamic thermal behaviour of a lubricant is lacking due to difficulties in direct measurement during operation. This research investigates an alternative approach using electrochemical impendence to measure the fluid film thickness under shear at various temperatures. A mineral oil and polyalphaolefin (PAO) were used as experimental models. Results showed that thermal properties of lubricants depended on the shear and were not a constant as is widely accepted. Analysis revealed that the mineral oil had higher dynamic thermal conductivity than that of PAO, due to their unique formulas This research discovered the possibility of dynamic properties of a working lubricant.

On the Influence of the Menthol Moiety on the Transport Properties of a Homologue Series of Functionalized Bis(trifluoromethylsulfonyl)imide Room-Temperature Ionic Liquids: A Quest for the Structure-Property Relationship.

This study explores the transport properties of bis(trifluoromethylsulfonyl)imide-based ionic liquids with a naturally derived (1R,2S,5R)-(−)-menthol moiety in the cationic part. In particular, we investigated the dependence of the dynamic viscosity and electrical conductivity as functions of the alkyl chain length. An important finding of this study is that both properties show nonmonotonic behavior with respect to the alkyl chain length. The nonmonotonic dependency is an obstacle for establishing the relationships between the structure and transport properties of homologues. To overcome this difficulty, we recommend fast property screening using a theoretical model that we developed, which allows for efficient viscosity prediction by means of the group contribution method. As demonstrated in this study, the model allows for reliable predictions of viscosity in the studied series with an overall relative deviation of less than 8%.

Performance prediction of asphalt mixture based on dynamic reconstruction of heterogeneous microstructure

This paper proposed an algorithm to reconstruct the microstructure of asphalt mixture considering dynamic arrangement process of aggregate particles. In this method, asphalt mixture was considered to be composed of dispersed phase including coarse aggregate and air voids, and continuous phase including fine asphalt matrix (FAM). The dispersed phase materials were characterized by high-dimensional polyhedral particles. In order to reconstruct the microstructure by 1:1 in volume fraction, three basic parameters that determine the heterogeneous structure of asphalt mixture were abided in the design of digital specimen. Then, impulse-based rigid collision response was introduced to simulate the rearrangement of aggregate particles in the compaction process of asphalt mixture. In particular, the applicability of the proposed method to typical structural types of asphalt mixture was discussed. For the asphalt mixture with high air void content, the reconstructed specimen may deviate from the real structure. Furthermore, the dynamic modulus and thermal conductivity of the generated specimens were predicted by finite element method (FEM) and compared with the experimental values. The predicted dynamic modulus and thermal conductivity coincide with the experimental results well, which indicates that the proposed method is reliable for reconstructing the heterogeneous structure of asphalt mixture with relatively low content of air voids.

Phase behaviors of chitosan/lignosulfonate mixed solutions

ABSTRACT The positively chitosan, CS, and negatively lignosulfonate, LGS, were statically mixed forming a series of mixed solutions. Experimentally, the light brown LGS solution was slowly flowed into the colorless CS solution to form the as-prepared CS/LGS mixed solutions. These mixing solutions presented regular bi-phases taking the LGS phase at the top and the CS phase at the bottom where the difference is the phase thickness varied with the mixing ratio variety. To keep the static mixing condition up to the 3rd, 12th and 15th days, these CS/LGS mixed solutions presented two-phase change tendencies because the CS percent greater samples kept the bi-phases and the LGS percent greater samples presented a tri-phases with a new darker yellow phase at the bottom and a new light yellow phase at the middle. This indicated that the statical mixing time has caused the electrostatic interaction occurrence between the CS and LGS solutions when the reaction degree was influenced by the mixing ratio. The particle size for the CS/LGS mixed solutions with the mixing ratio at 70/30 and 30/70 vol% both after static mixing of 15 days was analyzed and found it was smaller at about 200–300 nm in the upper phase and greater at about 1100–1300 nm in the bottom phase corresponding to the formed micelles and the precipitated aggregates, respectively. Recorded dynamic conductivity revealed that the electrostatic interaction between the CS and LGS strongly occurred after static mixing of about 300 s and the start time was controlled by the mixing ratio, especially the LGS percent.

Smoothed/profile lattice Boltzmann method for hydrothermal analysis of a corrugated parabolic-trough solar collector filled with nanofluid predicted by Koo–Kleinstreuer–Li model

PurposeThis study aims to employ a modern numerical approach for conducting the simulations, which uses the smoothed-profile lattice Boltzmann method. Two separate distribution functions for flow and temperature fields are used to solve the Navier–Stokes equations in the most efficient manner. In addition, the Koo–Kleinstreuer–Li model is used to calculate the dynamic viscosity and thermal conductivity in the desired volume fractions, and the effect of Brownian motion is taken into consideration.Design/methodology/approachNowadays, because of enhanced global price of oil and critical issue of global warming, a significant demand for using renewable energy exists. The solar energy is one of the most popular forms of renewable energy. The solar collector can be used to collect and trap the energy received from the sun. The present work focuses on introducing and investigating a parabolic-trough solar collector.FindingsTo analyze all hydrodynamic and thermal views of the solar collector, the structure of nanofluid stream, distribution of temperature, local dissipations because of flow and heat transfer, volumetric entropy production, Bejan number vs Rayleigh number and volume fraction are presented. Also, three different configurations for profile of solar receiver are designed and studied.Originality/valueThe originality of the present work is in using a modern numerical approach for a well-known application. Also, the effect of Brownian motion is taken into account which significantly enhances the accuracy.

Simulation study on the electric field of HVDC-GIL based on the dynamic conductivity model subjected to different current-carrying capacities

In this paper, we propose a thermal-electric coupling model based on the dynamic conductivity model, which considering the charge-trapping process. The charge accumulation characteristic under different current-carrying capacities was also investigated. The saturation time of average charge density and the average temperature in the space are approximate, which could be concluded that the charge accumulation is accompanied by the establishment of a temperature field. When the current-carrying capacity reaches 3000 A, the maximum surface electric field of the basin insulator will continue to rise 14.2% compared with 1500 A. The charge migration and accumulation near the enclosure results in a greatly distorted electric field near the triple junction of the ground enclosure. This paper could offer theoretical insights from a dielectric charge transport theory and perspective to be helpful for the design of spacer in HVDC-GIL.

Anomalous behaviour of dynamic electrical conductivity in semiconductor ferroelectric ceramics near the phase transition temperature

The article presents the results of a study of the electrical properties of semiconductor perovskite ceramics based on a solid solution of barium-strontium titanate with the addition of the rare earth element of cerium with the initial formula Ba1–x–y SrxCeyTiO3 (x = 0.05, y = 0.003). A scanning electron microscope was used to obtain images of the sample surfaces and the elemental composition data. The measurements were performed by impedance spectroscopy in the temperature range of 348-385 K in the frequency range of 102–106 Hz using an LCR metre. It was found that there is an anomalous behaviour in the dynamic electrical conductivity of the samples in the temperature range close to the ferroelectricparaelectricphase transition. This is expressed by a decrease in the value of the real part of the dynamic conductivity withan increase in frequency. An analysis of the simplified equivalent circuit of the intergranular barrier showed that this anomaly can be explained by introducing an inductive element into the circuit. This element can be considered a “negative capacitance element”. Following the results of the study, a conclusion was made about the generalised character of the phenomenon

Nonreciprocal guided waves in the presence of swift electron beams

Breaking the reciprocity of electromagnetic interactions is of paramount importance in photonic and microwave technologies, as it enables unidirectional power flows and other unique electromagnetic phenomena. Here we explore a method to break the reciprocity of electromagnetic guided waves utilizing an electron beam with a constant velocity. By introducing an effective dynamic conductivity for the beam, we theoretically demonstrate how nonreciprocal guided waves and a one-way propagating regime can be achieved through the interaction of swift electrons with electromagnetic waves in two-dimensional (2D) parallel-plate and three-dimensional (3D) circular-cylindrical waveguides. Unlike the conventional electron beam structures such as traveling wave tubes and electron accelerators, here the goal is neither to generate and/or amplify the wave nor to accelerate electrons. Instead, we study the salient features of nonreciprocity and unidirectionality of guided waves in such structures. The relevant electromagnetic properties such as the modal dispersion, the field distributions, the operating frequency range, and the nonreciprocity strength and its dependence on the electron velocity and number density are presented and discussed. Moreover, we compare the dispersion characteristics of waves in such structures with some electric-current-based scenarios in materials reported earlier. This broadband tunable magnet-free method offers a unique opportunity to have a switchable strong nonreciprocal response in optoelectronics, nanophotonics, and THz systems.

The role of interface on dynamic mechanical properties, dielectric performance, conductivity, and thermal stability of electrospun carbon nanofibers reinforced epoxy

AbstractPolymer nanocomposites containing pristine (PCNF) and amine‐functionalized (NFCNF) electrospun carbon nanofibers were fabricated. The amine‐terminated functional groups on CNFs, with a surface coverage of 2.76 mmol/g, react with the epoxy monomers forming covalent linkages for better dispersion and stronger interface. The improved load transfer resulted in an improvement of 82% in storage modulus (rubbery region~70°C) and 20°C increase in the glass transition temperature for 1 wt% NFCNF‐epoxy. Tensile strength and modulus improves by 22% and 27%, respectively, for 2 wt% NFCNF‐epoxy. The thermal stability, dielectric properties and AC/DC conductivity are discussed in terms of the interfacial characteristics. These results highlight the potential of electrospun CNFs as structural and functional reinforcement.