Anisotropic Conductivity Properties Research Articles

Anisotropic Superprotonic Conduction in a Layered Single-Component Hydrogen-Bonded Organic Framework with Multiple In-Plane Open Channels.

Hydrogen-bonded organic frameworks (HOFs) are promising proton conductive materials because of their inherent and abundant hydrogen-bonding sites. However, most superprotonic-conductive HOFs are constructed from multiple components to enable favorable framework architectures and structural integrity. In this contribution, layered HOF-TPB-A3 with a single component is synthesized and exfoliated. The exfoliated nanoplates exhibited anisotropic superprotonic conduction, with in-plane proton conductivities reaching 1.34×10-2 S cm-1 at 296 K and 98% relative humidity (RH). This outperforms the previously reported single-component HOFs and is comparable with the state-of-the-art multiple-component HOFs. The high and anisotropic proton conductive properties can be attributed to the efficient proton transport along multiple open channels parallel to their basal planes. Moreover, an all-solid-state (ASS) proton rectifier device is demonstrated by combining HOF-TPB-A3 and a hydroxide ion-conducting layered double hydroxide (LDH). This work suggests that single-component HOFs with multiple open channels offer more opportunities as versatile platforms for proton conductors, making them promising candidates for conducting media in protonic devices.

Validation of conductivity tensor imaging against diffusion tensor magnetic resonance electrical impedance tomography

Diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) and electrodeless conductivity tensor imaging (CTI) are two emerging modalities that can quantify low-frequency tissue anisotropic conductivity properties by assuming similar properties underlie ionic mobility and water diffusion. While both methods have potential applications to estimating neuro-modulation fields or formulating forward models used for electrical source imaging, a direct comparison of the two modalities has not yet been performed in-vitro or in-vivo. Therefore, the aim of this study was to test the equivalence of these two modalities. We scanned a tissue phantom and the head of human subject using DT-MREIT and CTI protocols and reconstructed conductivity tensor and effective low frequency conductivities. We found both gray and white matter conductivities recovered by each technique were equivalent within 0.05 S/m. Both DT-MREIT and CTI require multiple processing steps, and we further assess the effects of each factor on reconstructions and evaluate the extent to which different measurement mechanisms potentially cause discrepancies between the two methods. Finally, we discuss the implications for spectral models of measuring conductivity using these techniques. The study further establishes the credibility of CTI as an electrodeless non-invasive method of measuring low frequency conductivity properties.

Vertically aligned carbon fiber/polydimethylsiloxane composites prepared by lyophilization with exceptional thermal conductivity and electromagnetic interference shielding performance

Composites with high thermal conductivity and exceptional electromagnetic interference (EMI) shielding properties are crucial for ensuring the long-term stability of electronic devices. One-dimensional carbon fibers (CFs) stand out as promising materials due to their excellent thermal and electrical conductivity. However, the anisotropic nature of CFs limits the overall electrical and thermal conductivity of the composite, thus impeding its practical application. To address this limitation, we investigated the effect of different freezing methods on CF orientation using the ice template method. Subsequently, CF-150/PDMS and CF-250/PDMS composites with varying average lengths of CFs were prepared using the unidirectional freezing technique. We studied the influence of CF content and average length on the anisotropic thermal conductivity and EMI shielding properties of the composites. The CF-250/PDMS composite, with a CF content of 15.71 vol%, exhibits a remarkable thermal conductivity of 9.07 W·m−1·K−1 and a low thermal resistance of 2.61 °C·cm2‧W−1. The thermal conductive mechanism of CF/PDMS composites was simulated by thermal conduction model and finite element analysis. Furthermore, it demonstrates longitudinal electromagnetic interference shielding effectiveness (EMI SE) reaches up to 39.66 dB, while the transverse EMI SE reaches up to 52.55 dB. The vertically aligned CF/PDMS composites exhibit significant potential for a range of applications in thermal management and EMI shielding.

Electrical impedance myography method of measuring anisotropic tongue tissue

Objective. To date, measurement of the conductivity and relative permittivity properties of anisotropic biological tissues using electrical impedance myography (EIM) has only been possible through an invasive ex vivo biopsy procedure. Here, we present a novel forward and inverse theoretical modeling framework to estimate these properties combining surface and needle EIM measurements. Methods. The framework here presented models the electrical potential distribution within a monodomain, homogeneous, and three-dimensional anisotropic tissue. Finite-element method (FEM) simulations and tongue experimental results verify the validity of our method to reverse-engineer three-dimensional conductivity and relative permittivity properties from EIM measurements. Results. FEM-based simulations confirm the validity of our analytical framework, with relative errors between analytical predictions and simulations smaller than 0.12% and 2.6% in a cuboid and tongue model, respectively. Experimental results confirm qualitative differences in the conductivity and the relative permittivity properties in the x, y, and z directions. Conclusion. Our methodology enables EIM technology to reverse-engineer the anisotropic tongue tissue conductivity and relative permittivity properties, thus unfolding full forward and inverse EIM predictability capabilities. Significance. This new method of evaluating anisotropic tongue tissue will lead to a deeper understanding of the role of biology necessary for the development of new EIM tools and approaches for tongue health measurement and monitoring.

Magnet-oriented hydrogels with mechanical–electrical anisotropy and photothermal antibacterial properties for wound repair and monitoring

For hydrogel wound dressings, it remains a great challenge to simultaneously achieve multifunctional hydrogels with wound-matching mechanical performance, antibacterial activity and monitoring capability for the integration of treatment and rehabilitation training monitoring during wound repair. Inspired by the highly ordered hierarchical structures of natural soft tissues, ordered magnetoelectric nanosheet structures are introduced into gelatin-oxidized dextran (Gel-ODex) hydrogels to endow the hydrogel with anisotropy and versatility in this study. First, magnetoelectric nanosheets (Fe3O4-PDA-rGO, MPG) containing polydopamine (PDA) were obtained by dopamine (DA)-mediated formation of Fe3O4 nanoparticles in situ on the surface of reduced graphene oxide (rGO). Then, anisotropic Gel-ODex-MPG (GOH-MPG) hydrogels were prepared by introducing MPG into the Gel-ODex hydrogel network under a magnetic field. The GOH-MPG hydrogel exhibited anisotropic mechanical and conductive properties and great photothermal antibacterial performance under near-infrared light (NIR, 808 nm). In addition, the anisotropic GOH-MPG conductive hydrogel could accelerate infected wound healing and sensitively detect human movements, which is helpful for monitoring the wound status and for rehabilitation training during wound recovery. To the best of our knowledge, this was the first exploration of the combination of anisotropic hydrogels in the field of wound therapy and wearable sensors, which sheds light on developing anisotropic hydrogels with multifunctionality in tissue repair and personal health monitoring to realize the integration of treatment and rehabilitation training monitoring.

Anisotropic Hydrogels Constructed via a Novel Bilayer-Co-Gradient Structure Strategy toward Programmable Shape Deformation

The bilayer hydrogel actuators have attracted extensive attention for their unique stimulus-responsive properties. Most of the current research studies only focused on changing the constituent materials of two layers in the fixed bilayer structure to enhance the responsive deformability of bilayer hydrogels without involving the exploration on a structural level, which limited its further development. In this study, we proposed a novel bilayer-co-gradient structure constructed via a simple and low-cost structural programming strategy, which was self-assembled by introducing an embedded gradient structure into a single bilayer structure with the assistance of gradient-dissolved oxygen in nature. This multistructure endowed the hydrogel with a faster bending response than a single bilayer structure due to the synergistic asymmetry of the simple bilayer structure and the embedded gradient structure. It was found that the prepared hydrogels exhibited significantly anisotropic electrical conductivity and swelling properties. Moreover, the stimulus-responsive shape deformation exhibited superior temperature- and pH-based deformation programmability. Additionally, this hydrogel could serve as a hydrogel gripper to perform grasping behavior, which demonstrated that our study opens up a new route for designing and fabricating smart actuators.

Analysis of the structural, elastic constants, electronic, optical, dynamical, and thermodynamic in dicalcium silicate with various pressures

Theoretical simulation plays an increasingly important role in obtaining the structural characteristics and performance of materials. Using first-principles calculations, the structural, anisotropic elasticity, electronic properties, dynamics, and thermodynamics of Dicalcium Silicate (γ-Ca2SiO4 or γ-C2S) under a pressure of 0–10 GPa are studied. The optimized lattice constants and inter-atomic distances are consistent with other theoretical and experimental values, which shows that our simulation settings are reliable and give reasonable results. In addition to the structural data, we systematically studied the anisotropic elasticity, thermal conductivity, phonon, optical, and electronic properties of γ-C2S. The anisotropy of three-dimensional(3D) and two-dimensional(2D) projected Bulk modulus and Young's modulus are systematically analyzed. The calculation results show that the γ-C2S has mechanical stability, and the system has significant anisotropy. In addition, according to the density functional perturbation theory (DFPT), the infrared active and inactive vibration modes are given and analyzed. This study shows that γ-C2S is also dynamically stable. Finally, through the phonon method and the quasi-harmonic Debye model method, heat capacity Cv and entropy S are calculated and analyzed in the temperature range of 0–700 K. We also found that the present work can give a reference to those not to be experimentally investigated.

Improving conductivity and self-sensing properties of magnetically aligned electroless nickel coated glass fiber cement

The nickel coated glass fiber (Ni-GF) cement (NGFC) holds promise for self-sensing concrete structure due to its improved conductivity and corrosion resistance. This paper is aimed at evaluating the conductivity and self-sensing properties of preferentially orientated NGFC, which was prepared by the magnetic field (MF) induction. The microstructure of electroless Ni-GFs and their arrangement characteristic in cement were observed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The anisotropic conductivity and self-sensing properties of as-prepared composites were measured by four-electrode method. The results indicate that the Ni-GFs with uniform nickel coating layer in the as-fabricated composite have an excellent alignment effect under the MF induction. When the Ni-GF content is 2.62 vol%, the composite exhibits maximum anisotropy. The order of the electrical resistivity and percolation thresholds of NGFC is: parallel to MF < without MF < perpendicular to MF. Under the cyclic compression load, the NGFC parallel to MF shows the optimum self-sensing properties. With the increase of loading amplitude and decrease of loading rate, the maximum sensitivities of the as-prepared composite at all directions almost increase linearly. Under the failure compression load, the conductivity of as-prepared composites parallel to MF show a steadier and higher self-sensing response.

Tailored carbon-based aramid nanofiber nanocomposites with highly anisotropic thermal conductivity and superior mechanical properties for thermal management

Polymer nanocomposites show great potential as thermal management materials owing to their light weight and high design freedom. However, they often suffer from the inability of integrating a high thermal conductivity, satisfactory mechanical properties, and even elevated temperature resistance for real-world scenarios. Here we tailor high-performance carbon-based aramid nanofiber (ANF) nanocomposites toward highly anisotropic thermal conductivity and superior mechanical properties through a vacuum-filtration-induced self-assembly process. The as-obtained ANF nanocomposite films exhibit a unique hierarchical structure composed of horizontally stacked carbon fillers in the ANF matrix, thereby achieving a high in-plane thermal conductivity of 20.54 Wm−1K−1 at only 20 wt% graphene nanosheet loading and anisotropy factors of over 100. Further finite element simulations and proof-of-concept applications for high-power light-emitting diode chip cooling demonstrate the excellent heat dissipation performance of the resulting nanocomposite film. More importantly, the tailored ANF nanocomposite films exhibit high mechanical robustness, high flexibility, superb thermal stability, and flame retardancy, making them extremely promising for thermal management applications in various electronic devices.

Ultrathin, Ultralight, and Anisotropic Ordered Reduced Graphene Oxide Fiber Electromagnetic Interference Shielding Membrane

AbstractDeveloping an electromagnetic interference (EMI) shielding material with lightweight, ultrathin, and high‐performance complex electromagnetic wave pollution has become a research trend. Here, a novel ultrathin ordered reduced graphene oxide fiber (oRGOF) membranes are reported with wrinkles, grooves, and hierarchical structure by a simple assembly process based on wet spinning. The results show that the oRGOF membranes have obvious anisotropic conductivity and directional electromagnetic shielding properties. The measured electrical conductivity along the fiber axial direction (0°) is higher than that along the fiber radial direction (90°). Furthermore, the EMI shielding performance difference under different rotation angles is more than 25 dB (31.0 dB at 0°, 4.9 dB at 90°). The thickness of the resultant oRGOF membrane is 0.03 mm and area density of 0.9 mg cm−2, and the specific EMI SE (SSE/t) is 33333 dB cm2 g−1 along the fiber axis. The oRGOF membranes show flexible and durable performance under repeated bending and straightening cycles tests over 160 times, without significant reduction of the shielding performance. Thus, the ultrathin, ultralight, and anisotropic oRGOF electromagnetic interference shielding membrane have broad prospects for both civilian and military applications.

Zintl Phase BaAgSb: Low Thermal Conductivity and High Performance Thermoelectric Material in Ab Initio CalculationSupported by the National Key R&D Program of China (Grant Nos. 2016YFA0401503 and 2017YFA0403700), the National Natural Science Foundation of China (Grant Nos. 11675255, U1932220, 11675195, and U1932220), the Key Research Program of Frontier Sciences, CAS (Grant No. 292016YQYKXJ00135), and the Program of State Key Laboratory

Thermoelectric materials are critical parts in thermal electric devices. Here, Zintl phase BaAgSb in space group of P63/mmc is reported as a promising thermoelectric material in density function theory. The anisotropic lattice thermal conductivity and phonon transport properties are investigated in theory. The strong phonon-phonon scattering in BaAgSb exhibits ultra-low lattice thermal conductivity of 0.59 W⋅m−1⋅K−1 along c-axis at 800 K, and high thermoelectric performance ZT = 0.94 at 400 K. The mix of covalent and ionic bond supports high carrier mobility and low thermal conductivity. The unusual features make BaAgSb a potential thermoelectric material.

Magnetic aligned sulfonated carbon nanotube/Nafion composite membranes with anisotropic mechanical and proton conductive properties

Nafion composite membranes with various amounts of sulfonated multi-walled carbon nanotubes (Su-CNTs) were prepared either in or without a strong magnetic field. Interestingly, it is found that being recast in a strong magnetic field, the tensile strength at break and proton conductivity of Su-CNTs/Nafion composite membranes parallel to the magnetic field direction were higher than those perpendicular to magnetic field. Remarkably, such anisotropic mechanical property and proton conductivity of Su-CNTs/Nafion composite membranes strongly depend on water uptake and temperature, in particular the content of Su-CNTs. Quite a different dependence of the proton conductivity of the composite membranes on Su-CNT content, relative humidities and temperatures is well explained for the anisotropic proton conductivity of the Su-CNTs/Nafion membrane recast in a strong magnetic field, which is attributed to the preferential proton transporting along ionic water channels mainly coalesced by the orientated Su-CNTs at a specific water uptake. For Nafion composite membranes with 5 wt.% Su-CNTs, the proton conductivity along the direction of treating magnetic field approaches to 0.216 S/cm, which is $$\sim$$ 46% higher than that perpendicular to the magnetic field at 95 $$^{\circ }$$ C. The present work provides a deep insight of the humidity and temperature dependence of proton conductivity of Su-CNTs/Nafion composite membranes and a new strategy for fabrication proton exchange membranes with high proton conductivity as well as good mechanical property.

Enhanced mechanical and anisotropic thermal conductive properties of polyimide nanocomposite films reinforced with hexagonal boron nitride nanosheets

AbstractTo attain thermally conductive but electrically insulating polymer films, in this study, polyimide (PI) nanocomposite films with 1–30 wt% functionalized hexagonal boron nitride nanosheets (BNNSs) were fabricated via solution casting and following imidization. The microstructures, mechanical and thermal conductive properties of PI/BNNS nanocomposite films were examined by taking account of the relative content, anisotropic orientation, and interfacial interaction of BNNS and PI matrix. The scanning electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffractometry data revealed that BNNSs with hydroxy and amino functional groups have specific molecular interactions with PI matrix and they form stacked aggregates in the nanocomposite films with high BNNS loadings of 10–30 wt%. The tensile mechanical strength/modulus, thermal degradation temperatures, and thermal conductivity of the nanocomposite films were found to be significantly enhanced with increasing the BNNS loadings. For the nanocomposite films with 1–30 wt% BNNS loadings, the in‐plane thermal conductivity was measured to be 1.82–2.38 W/mK, which were much higher than the out‐of‐plane values of 0.35–1.14 W/mK. The significant anisotropic thermal conductivity of the nanocomposite films was found to be owing to the synergistic anisotropic orientation effects of both BNNS and PI matrix. It is noticeable that the in‐plane and out‐of‐plane thermal conductivity values of the nanocomposite film with 30 wt% BNNS were ~1.31 and ~3.35 times higher than those of neat PI film, respectively.

Heat and mass transfer inside of a monolith honeycomb: From channel to full size reactor scale

This paper is devoted to the multi-scale model of the heat and mass transfer inside of a honeycomb monolith substrate. Due to computational limitations, monoliths are modelled as a continuum in full-scale catalytic reactors models. That makes it necessary to use correlations or sub-models derived from channel scale results to account for a physically consistent heat and mass transfer inside of the substrate. In this paper detailed computational models at a channel and reactor scales are analyzed. Catalytic oxidation of CO is used as a reaction and the fluid properties are considered to be temperature-dependent. First, a channel scale model is used to analyze Nusselt, Sherwood, Lewis, and Damköhler numbers inside of the monolith channels. Secondly, sub-models obtained at a channel level are implemented in a full-scale reactor model using the continuum approach, to evaluate the impact of using detailed vs. highly simplified correlations for heat and mass transfer. The reactor scale model accounts for the transitions of the flow regime, entrance length effects, an-isotropic substrate thermal conductivity and temperature-dependent fluid properties. According to the results, the Lewis number can deviate significantly from one in the entrance length, however, it approaches asymptotically to unity as the flow develops. Regarding Nusselt and Sherwood, current interpolating methodologies are not able to predict the correct value in the entrance region when Damköhler is low, nonetheless, are reasonably accurate for the asymptotic one.

A New Highly Anisotropic Rh-Based Heusler Compound for Magnetic Recording.

The development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat-assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc , coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2 CoSb is introduced as a new hard magnet with potential for thin-film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m-3 is combined with a saturation magnetization of μ0 Ms = 0.52 T at 2 K (2.2 MJ m-3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare-earth-free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin-orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m-1 K-1 , make Rh2 CoSb a candidate for the development of heat-assisted writing with a recording density in excess of 10Tb in.-2 .

Printed hydrogel nanocomposites: fine-tuning nanostructure for anisotropic mechanical and conductive properties

Additive manufacturing of composites offers a potential for a new level of control over a material’s structure at the microscale. The focus of this work is a 2-hydroxyethyl methacrylate (HEMA)–based gelation system with orderly distributed carbon nanotubes (CNTs). CNTs undergo shear-induced alignment during printing process, and retain their orientation after the polymerisation of HEMA monomers, thereby, forming a nanocomposite with anisotropic mechanical and electrical properties. It is characterised with an intensive programme of mechanical tests including quasistatic uniaxial stretching, and dynamic cyclic loadings, as well as its four-terminal sensing of conductive characteristics. A coupling effect of mechanical and electrical properties is also studied. The experimental findings are discussed in detail and demonstrate that the orientation of CNTs affects both the mechanical and electrical conductive properties of the nanocomposites in terms of its ultimate strength, resistivity, and a piezoresistive coefficient. Understanding of anisotropic electromechanical properties of printed PHEMA-CNT hydrogel nanocomposite will ultimately underpin the development of smart soft materials for diverse applications, such as biomimetic nucleus pulposus or flexible electronics.

Alumina aerogels with unidirectional channels under different freezing temperatures during freeze casting——Part II: Anisotropic mechanical and thermal conductive properties

The anisotropic mechanical and thermal conduction properties of unidirectional aligned alumina aerogels (AAs) were investigated in our part II. The anisotropic structure characteristics are the main factors to decide the physical properties of AAs. The results show that the brittle failure behavior reflects the fracture of the long pore walls along ice-crystal growth direction, but the excellent strain and low compressive strength are ascribed to the weak second structures. The structural difference in the direction of heat transfer results anisotropic thermal conduction. The heat transfers layer-by-layer at intervals of solid walls and air pores is more effective for the heat insulation.

Fabrication of thermoplastic functionally gradient composite parts with anisotropic thermal conductive properties based on multicomponent fused deposition modeling 3D printing

Abstract A multicomponent fused deposition modeling 3D printing approach was proposed to fabricate thermoplastic functionally gradient composite parts (TFGCPs). The thermal conductive properties of the fabricated TFGCPs were studied by slice and as integrate, respectively. The variation of thermal conductivity by slice versus the number of layer shows that the curve of PCL/AlN has a constant slope, while the one of PCL/BN first increases and then decreases. It is attributed to that the network of thermal conduction is constructed when the loading of BN particles approaches 27wt%, leading to a substantial growth in thermal conductivity. The thermal conductivity of the TFGCPs as integrate lies between the one of pure PCL and homogeneous composite parts with AlN or BN fillers and has a relationship with the filler loading direction exhibiting thermal anisotropy. This study establishes the relationship between properties and structures of thermoplastic functionally gradient composite parts, which helps to lay a theoretical foundation of applications as intermediate layers.

Preparation and characterization of coatings with anisotropic thermal conductivity

The temperature increase caused by a concentrated heat source can affect the performance of electronic components inside spacecraft. Therefore, the development of an advanced thermal control system is essential for maintaining them in a safe temperature range. For this purpose, anisotropic thermal conductive coatings consisting of phenolic formaldehyde resin (PF) and pyrolytic graphite sheets (PGS) have been prepared in this work. The area of the heat-affected zone produced by a high-energy continuous wave laser is calculated to estimate the thermal diffusivity along the horizontal direction of the coating, whereas the thermal insulating capacity in the vertical direction is determined by measuring the back-surface temperature of the aluminum substrate. The obtained results show that the introduction of PGS noticeably improves the thermal diffusivity of coating, leading to a decrease in its back-surface temperature. After irradiating the coating containing three pieces of PGS with laser at a power density of 1500 W/cm2 for 10 s, its back-surface temperature is only 29 °C, which is much lower than that of the coating fabricated from pure PF (190 °C). Hence, the prepared coatings exhibit excellent anisotropic thermal conductive properties and can be potentially used as protective shields for spacecraft electronics.

Electric-field-induced out-of-plane alignment of clay in poly(dimethylsiloxane) with enhanced anisotropic thermal conductivity and mechanical properties

An Alternating current (AC) electrical field was applied to induce the movement of the clay nanoparticles in polydimethylsiloxane (PDMS) to fabricate flexible membranes embedded with thickness-direction aligned nanoparticles. The influence of the electric field strength and frequency on the movement of the particles in the PDMS monomer was investigated using an optical microscope. The morphology of the aligned clay/PDMS membranes frozen with thermal curing was analyzed with scanning electron microscopy (SEM) and confocal Raman spectroscopy. Benefiting from the anisotropic structure of aligned particle chains, the aligned clay/PDMS membranes show enhanced mechanical properties, thermal conductivity, and the light transmittance in the thickness direction compared to nonaligned membranes. This enhancement effect decreases as the particle concentration exceeds 5 wt %. The reason is that at higher clay concentrations, alignment of the particle is frustrated and particle chains become tilted and irregular owing to an increment in the viscosity of the system.