Inherent Structural Anisotropy Research Articles

Crystallographically Textured Electrodes for Rechargeable Batteries: Symmetry, Fabrication, and Characterization.

The vast of majority of battery electrode materials of contemporary interest are of a crystalline nature. Crystals are, by definition, anisotropic from an atomic-structure perspective. The inherent structural anisotropy may give rise to favored mesoscale orientations and anisotropic properties whether the material is in a rest state or subjected to an external stimulus. The overall perspective of this review is that intentional manipulation of crystallographic anisotropy of electrochemically active materials constitute an untapped parameter space in energy storage systems and thus provide new opportunities for materials innovations and design. To that end, we contend that crystallographically textured electrodes, as opposed to their textureless poly crystalline or single-crystalline analogs, are promising candidates for next-generation storage of electrical energy in rechargeable batteries relevant to commercial practice. This perspective is underpinned first by the fundamental─to a first approximation─uniaxial, rotation-invariant symmetry of electrochemical cells. On this basis, we show that a crystallographically textured electrode with the preferred orientation aligned out-of-plane toward the counter electrode represents an optimal strategy for utilization of the crystals' anisotropic properties. Detailed analyses of anisotropy of different types lead to a simple, but potentially useful general principle that "Pec//Pc" textures are optimal for metal anodes, and "Pec//Sc" textures are optimal for insertion-type electrodes.

Photocatalytic properties of anisotropic β-PtX2 (X = S, Se) and Janus β-PtSSe monolayers.

The highly efficient photocatalytic water splitting process to produce clean energy requires novel semiconductor materials to achieve a high solar-to-hydrogen energy conversion efficiency. Herein, the photocatalytic properties of anisotropic β-PtX2 (X = S, Se) and Janus β-PtSSe monolayers were investigated based on the density functional theory. The small cleavage energy for β-PtS2 (0.44 J m-2) and β-PtSe2 (0.40 J m-2) endorses the possibility of mechanical exfoliation from their respective layered bulk materials. The calculated results revealed that the β-PtX2 monolayers have an appropriate bandgap (∼1.8-2.6 eV) enclosing the water redox potential, light absorption coefficient (∼104 cm-1), and exciton binding energy (∼0.5-0.7 eV), which facilitates excellent visible-light-driven photocatalytic performance. Remarkably, the inherent structural anisotropy leads to an anisotropic high carrier mobility (up to ∼5 × 103 cm2 V-1 S-1), leading to a fast transport of photogenerated carriers. Notably, the required small external potential to realize hydrogen evolution reaction and oxygen evolution reaction processes with an excellent solar-to-hydrogen energy conversion efficiency for β-PtSe2 (∼16%) and β-PtSSe (∼18%) makes them promising candidates for solar water splitting applications.

Autonomous materials systems from active liquid crystals

Liquid crystals (LCs) are ubiquitous in display technologies. The orientational ordering in the nematic phase of LCs gives rise to structural anisotropy, the ability to form topological defects and extraordinary sensitivity to interfacial events — three features that are not found in traditional, isotropic liquids. Active LC systems represent a particular class of active materials, in which some form of energy is transformed and used to generate motion, providing opportunities for new technologies and offering a platform to investigate matter far from equilibrium. In this Review, we discuss recent advances in the field of active LC systems, including natural systems, such as cell colonies, biopolymers and bacteria, and synthetic systems, which mimic the adaptive and autonomous behaviours found in nature. We investigate the properties of defects and flows, examine LC interfaces and emulsions, and discuss active LC colloids and composites. Finally, we highlight future possibilities and applications of active LC systems. Active liquid crystals are a particular type of active materials in which an inherent structural anisotropy leads to long-range order and topological defects. This Review discusses natural and synthetic active liquid crystals, and explores their autonomous behaviour as well as potential applications.

Recent Advance of Tellurium for Biomedical Applications

Tellurium(Te) nanomaterials have aroused a wide interest in semiconductor, thermoelectric, piezoelectric, as well as biomedical applications. The last decades of reports indicated a major nanostructure of one-dimensional (1D) Te on account of its inherent structural anisotropy. Two-dimenional(2D) Te has been newly developed and drawn a lot of interests recently. This review presents the intrinsic biological potential of Te-based nanomaterials and summarizes their up-to-date advance in phototherapy and reactive oxygen species(ROS)-related applications in the biomedical field.

Using the Pietruszczak-Mroz anisotropic failure criterion to model the strength of stratified rocks

The strength of stratified rocks is closely related to their inherent structural anisotropy, which cannot be accurately represented by the isotropic failure criteria. In this study, the Pietruszczak-Mroz (PM) anisotropic failure criterion was used to describe the directional dependency of strength of stratified rocks. In the meridian plane, the frictional coefficient was established by incorporating an anisotropic variable defined as a joint invariant of fabric and stress tensors. In the deviatoric plane, the anisotropic failure surface was characterized by a smooth shape function of Lode's angle. The material parameters for the failure criterion can be determined using the triaxial test. The PM anisotropic criterion was utilized to predict the anisotropic strength of specific stratified rocks. Analysis of the experimental data validated the assertion that PM anisotropic criterion has excellent ability to model the anisotropic strength features of stratified rocks.

Anisotropic Thermal Transport in Spray-Coated Single-Phase Two-Dimensional Materials: Synthetic Clay Versus Graphene Oxide.

Directional control on material properties such as mechanical moduli or thermal conductivity are of paramount importance for the development of nanostructured next-generation devices. Two-dimensional materials are particularly interesting in this context owing to their inherent structural anisotropy. Here, we compare graphene oxide (GO) and synthetic clay sodium fluorohectorite (Hec) with respect to their thermal transport properties. The unique sheet structure of both allows preparation of highly ordered Bragg stacks of these pure materials. The thermal conductivity parallel to the platelets strongly exceeds that perpendicular to them. We find a significant difference in the performance between GO and synthetic clay. Our analysis of the textured structure, size of the platelets, and chemical composition shows that Hec is a superior two-dimensional component to GO. Consequently, synthetic clay is a promising material for thermal management applications in electronic devices where electrically insulating materials are prerequisites.

Effect of structural phase transitions on high temperature thermal conductivity of nuclear-grade uranium

Abstract Reliable experimental evaluation of thermal conductivity of nuclear-grade uranium over a wide temperature range from 298 K to 1273 K, encompassing both of its solid-state allotropic phase transformations has been carried out for the first time using thermal diffusivity and linear thermal expansion data. Temperature dependence of both diffusivity and expansivity showed abrupt break at both the phase transitions namely, orthorhombic (α-phase) to tetragonal (β-phase) at 948 K and tetragonal (β-phase) to cubic (γ-phase) at 1051 K. Thermal conductivity also increases abruptly upon uranium undergoing structural modification from ambient temperature orthorhombic phase to high temperature cubic phase. Observed differences in results obtained in present investigation from those reported in literature have been explained on the basis of non-metallic impurity contents and inherent structural anisotropy of uranium. It has been suggested that structural anisotropy, which strongly affects metal’s microstructure; also notably influences the heat transport properties. High temperature body centred cubic phase (BCC) of uranium shows very high heat conductivity (44 W/m.K at 1075 K), which affirms the advantage of cubic-phase uranium alloys as potential metallic nuclear fuel. Presented results will be highly useful for development of uranium-based metallic alloy fuels.

Tellurene: its physical properties, scalable nanomanufacturing, and device applications.

Tellurium (Te) has a trigonal crystal lattice with inherent structural anisotropy. Te is multifunctional, e.g., semiconducting, photoconductive, thermoelectric, piezoelectric, etc., for applications in electronics, sensors, optoelectronics, and energy devices. Due to the inherent structural anisotropy, previously reported synthetic methods predominantly yield one-dimensional (1D) Te nanostructures. Much less is known about 2D Te nanostructures, their processing schemes, and their material properties. This review focuses on the synthesis and morphology control of emerging 2D tellurene and summarizes the latest developments in understanding the fundamental properties of monolayer and few-layer tellurene, as well as the recent advances in demonstrating prototypical tellurene devices. Finally, the prospects for future research and application opportunities as well as the accompanying challenges of 2D tellurene are summarized and highlighted.

Natural extracted aerogels with inherent anisotropy and their 3D printing assisted biomedical applications.

Exemplified with jackfruit and sugarcane, natural extracted aerogels with inherent structural anisotropy were investigated for the first time. With the help of nano-modification, the dual liquid/current directing capability of the Ag decorated jackfruit aerogel was discovered. This interesting material was then applied as the core component of a 3D printed wearable device for intelligent wound management. The as-prepared ultra-light (<10 g) wearable device could provide drainage diversion, wound warning and triple antibacterial treatment in a continuous and automatic manner.

Pore orientation mediated control of mechanical behavior of scaffolds and its application in cartilage-mimetic scaffold design

Scaffolds with aligned pores are being explored in musculoskeletal tissue engineering due to their inherent structural anisotropy. However, influence of their structure on mechanical behavior remains poorly understood. In this work, we elucidate this dependence using chitosan–gelatin based random and aligned scaffolds. For this, scaffolds with horizontally or vertically aligned pores were fabricated using unidirectional freezing technique. Random, horizontal and vertical scaffolds were characterized for their mechanical behavior under compressive, tensile and shear loading regimes. The results revealed conserved trends in compressive, tensile and shear moduli, with horizontal scaffolds showing the least moduli, vertical showing the highest and random showing intermediate. Further, these scaffolds demonstrated a highly viscoelastic behavior under cyclic compressive loading, with a pore orientation dependent relative energy dissipation. These results established that mechanical behavior of porous scaffolds can be modulated by varying pore orientation alone. This finding paved the way to recreate the structural and consequent mechanical anisotropy of articular cartilage tissue using zonally varied pore orientation in scaffolds. To this end, monolithic multizonal scaffolds were fabricated using a novel sequential unidirectional freezing technique. The superficial zone of this scaffold had horizontally aligned pores while the deep zone consisted of vertically aligned pores, with a transition zone between the two having randomly oriented pores. This depth-dependent pore architecture closely mimicked the collagen alignment of native articular cartilage which translated into similar depth-dependent mechanical anisotropy as well. A facile fabrication technique, biomimetic pore architecture and associated mechanical anisotropy make this multizonal scaffold a promising candidate for cartilage tissue engineering.

Modelling of coupled electron and mass transport in anisotropic proton-exchange membrane fuel cell electrodes

As one of the key components of proton-exchange membrane fuel cells, the gas-diffusion layer (GDL) that is made of carbon fibres usually exhibits strong structural anisotropy. Nevertheless, the GDL has traditionally been simplified as a homogeneous porous structure in modelling the transport of species through the GDL. In this work, a coupled electron and two-phase mass transport model for anisotropic GDLs is developed. The effects of anisotropic GDL transport properties due to the inherent anisotropic carbon fibres and caused by GDL deformations are studied. Results indicate that the inherent structural anisotropy of the GDL significantly influences the local distribution of both cathode potential and current density. Simulation results further indicate that a GDL with deformation results in an increase in the concentration polarization due to the increased mass-transfer resistance in the deformed GDL. On the other hand, the ohmic polarization is found to be smaller in the deformed GDL as the result of the decreased interfacial contact resistance and electronic resistance in the GDL. This result implies that an optimum deformation needs to be achieved so that both concentration and ohmic losses can be minimized.

The effects of topology upon fluid-flow and heat-transfer within cellular copper structures

The fluid-flow and heat-transfer features of cellular metal lattice structures made from copper by transient liquid phase (TLP) bonding and brazing of plane weave copper meshes (screens) were experimentally characterized under steady-state forced air convection. Due to the inherent structural anisotropy of this metal textile derived structure, the characterizations were performed for several configurations to identify the preferable orientation for maximizing thermal performance as a heat dissipation medium. Results show that the friction factor of bonded wire screens is not simply a function of porosity as stochastic materials such as open-celled metal foams and packed beds, but also a function of orientation (open area ratio). The overall heat transfer depends on porosity and surface area density, but only weakly on orientation. Comparisons with stochastic metal foams and other heat dissipation media such as packed beds, louvered fins and microtruss lattice cellular materials suggest that wire-screen meshes compete favorably with the best available heat dissipation media. The overall thermal efficiency index of the copper textiles-based media is approximately three times larger than that of stochastic copper foams, principally because of the lower pressure drop encountered during coolant propagation through the periodic wire-screen structure.

Convective heat dissipation with lattice-frame materials

This paper presents experimental results on heat transfer and pressure drop for a compact heat sink made of fully triangulated, lightweight (porosity ∼ 0.938), aluminum lattice-frame materials (LFMs). Due to the inherent structural anisotropy of the LFMs, two mutually perpendicular orientations were selected for the measurements. Constant heat flux was applied to the heat sink under steady state conditions, and dissipated by forced air convection. The experimental data were compared with those predicted from an analytical model based on fin analogy. The experimental results revealed that pressure drop is strongly dependent upon the orientation of the structure, due mainly to the flow blockage effect. For heat transfer measurements, typical local temperature distributions on the substrate under constant heat flux conditions were captured with infrared camera. The thermal behavior of LFMs was found to follow closely that of cylinder banks, with early transition Reynolds number (based on strut diameter) equal to about 300. The Nusselt number prediction from the fin-analogy correlates well with experimental measurements, except at low Reynolds numbers where a slightly underestimation is observed. Comparisons with empty channels and commonly used heat exchanger media show that the present LFM heat sink can remove heat approximately seven times more efficient than an empty channel and as efficient as a bank of cylinders at the same porosity level. The aluminum LFMs are extremely stiff and strong, making them ideal candidates for multifunctional structures requiring both heat dissipation and mechanical load carrying capabilities.

New Aspects of Gravity Responses in Plant Cells

Plants show two distinct responses to gravity: gravity-dependent morphogenesis (gravimorphogenesis) and gravity resistance. In gravitropism, a typical mechanism of gravimorphogenesis, gravity is utilized as a signal to establish an appropriate form. The response has been studied in a gravity-free environment, where plant seedlings were found to perform spontaneous morphogenesis, termed automorphogenesis. Automorphogenesis consists of a change in growth direction and spontaneous curvature in dorsiventral directions. The spontaneous curvature is caused by a difference in the capacity of the cell wall to expand between the dorsal and the ventral sides of organs, which originates from the inherent structural anisotropy. Gravity resistance is a response that enables the plant to develop against the gravitational force. To resist the force, the plant constructs a tough body by increasing the cell wall rigidity that suppresses growth. The mechanical properties of the cell wall are changed by modification of the cell wall metabolism and cell wall environment, especially pH. In gravitropism, gravity is perceived by amyloplasts in statocytes, whereas gravity resistance may be mediated by mechanoreceptors on the plasma membrane.

Holographic interferometry of intact and radially incised human eye-bank corneas

Many methods to measure corneal elasticity destroy the tissue and thereby produce erroneous results. Holographic interferometry, a highly precise nondestructive optical comparison technique, was used to evaluate corneal elasticity of intact eye-bank eyes. A double-pulse holographic interferometer operating at 632.8 nm was used to measure corneal deformation in 20 whole-globe eyes from donors 45 to 83 years of age for intraocular pressures from 16 mm Hg to 21 mm Hg. Stress was computed from LaPlace's law, and arc length strain was derived from z-axis distention of the central cornea. The stress-strain relationship in the normal physiological range of intraocular pressure was linear with a Young's elastic modulus of 1.03 gigapascals for the central cornea (r = 0.999). During interferometry of radial keratotomy of the cornea, interference fringe patterns developed in association with each incision as it was made. When four incisions were placed deep along each of the primary semimeridians, the fringe pattern developed as expected, based on current keratotomy models. When incisions were shallow (∼50% depth) and placed asymmetrically along the nasal, temporal, and superior semimeridians, the resulting surface strain was symmetrical about the central cornea, forming an annular pattern of interference fringes. These results indicate that when the cornea was stressed at physiological pressures as part of the intact whole globe, it was less elastic than excised corneal tissue tested by strip extensiometry. Radially incised corneas demonstrated strain patterns suggestive of inherent structural anisotropy with a possible inferior quadrant weakness.

Rubber Birefringence and Photoelasticity

Abstract The phenomenon of birefringence, discovered in 1669 by Erasmus Bartholin and later studied by Christian Huygens, is well known for its appearance in transparent crystalline solids. It is to be traced essentially to internal anisotropy of crystals for light propagation, so that under certain conditions a single wave front may give rise to multiple coherent waves which can cause double refraction or other phenomena such as the appearance of fringes varying in brightness and color due to interference of emerging wave fronts. Birefringence may be expressed as the difference of the velocities of propagation in various directions in the birefringent medium and particularly as the difference between the maximum and the minimum velocity or, alternatively, between the maximum and the minimum refractive index or even as the phase difference between emerging waves, given frequently as a number of wavelengths. While true double refraction phenomena may be observed with ordinary light when the difference n1−n2 between the refractive indexes is very high, the interference phenomena may be obtained only with polarized light, but may be observed even with very small differences between indexes. This is not the place to treat extensively general concepts like polarizer, analyzer, ordinary wave, extraordinary wave, uniaxial crystal, biaxial crystal, etc. which can be found in any good optics treatise. Birefringence is not in any way limited to crystalline media, possessing inherent structural anisotropy. It may also appear in bodies which are normally isotropic, when structural anisotropy is caused by external forces. Then birefringence is quantitatively dependent on force intensities, even if not always in an easily detectable way. This is called “accidental birefringence” or “stress-birefringence”. It was observed by Seebeck in 1813, and later studied in 1816 by Brewster for glass. It is observable in many transparent materials. Stress-birefringence is particularly conspicuous in macromolecular substances, including elastomers, vulcanized or not, where it is determined by the orientation of molecular links. This, of course, may not be ascribed altogether to stress, but sometimes also to partial crystallinity. Other phenomena of accidental birefringence may be observed in liquids or in solutions, especially of elastomers, when they are subjected to a velocity gradient, as when flowing through a capillary tube or, more commonly, when sheared between two coaxial cylinders.