Wavy Structure Research Articles

Structural Design of Nanowire Wearable Stretchable Thermoelectric Generator.

Wearable thermoelectric generators as renewable energy conversion technologies have witnessed rapid development in the past decade. Herein, we design a nanowire (NW) film wavy structure which possesses an excellent temperature gradient ratio for stretchable thermoelectric generators. Taking advantage of the photothermal effect of Te NWs as the hot side and p-n NWs heterofilms (n-type Ag2Te and p-type Cu1.75Te NWs) as thermoelectric materials, a considerable output voltage can be achieved under light irradiation. Besides the electricity output, the wearable device can also make our skin warm and comfortable in cold weather. Meanwhile, we combine thermoelectric generators with passive radiative cooling technology to reduce insolation of the human body and improve the performance of the device under intense solar irradiation in hot weather. Interestingly, it can also offer continuous green energy to realize various signal perceptions, suggesting a robust strategy for electricity output and self-powered wearable electronics.

Dynamic stretching–electroplating metal‐coated textile for a flexible and stretchable zinc–air battery

AbstractA metal electrode is a significant component of a zinc–air battery (ZAB), but the metal material is usually not elastic, which severely restricts the application of flexible and stretchable ZABs in the field of wearable electronic devices. Herein, we report a flexible and stretchable metal‐coated textile prepared by a dynamic stretching–electroplating based on a wavy spandex textile substrate. Benefiting from the unique woven and wavy structure, the metal‐coated textile shows a high stretchability of 100% and stable conductivity. In situ scanning electron microscope observation during stretching showed that the tensile strain of the metal‐coated textile is mainly attributed to the deformation of the microfiber network at the bottom position of the wave structure. In addition, a sodium carboxymethyl cellulose–polyacrylic acid–potassium hydroxide composite hydrogel has been used as the electrolyte. This hydrogel shows excellent ionic conductivity, mechanical properties, and water retention properties, which makes it suitable for the semi‐open system of ZAB. Furthermore, a flexible and stretchable sandwich‐structure ZAB, assembled using the above‐mentioned electrodes and electrolyte, operates stably even under rapid stretching/releasing cycle deformation. Because of its facile preparation and low cost, this flexible and stretchable ZAB is suitable for fabrication of large‐area batteries to obtain higher output current and power to drive wearable electronic devices.

Investigation of interface microstructure and properties of copper/304 stainless steel fabricated by explosive welding

Explosive welding is a solid state welding process that is used for the metallurgical joining of two or more dissimilar metals. This paper presented a systematic study of microstructure and properties of copper/304 stainless steel fabricated by explosive welding. The microstructure and chemical composition were evaluated using Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The properties were performed by the nanoindentation tests and bending experiments of the microcantilevers, and the microcantilevers were milled out using the Focused Ion Beam (FIB) system. The results showed that the interface between this couple metals presents a typical wavy structure. There are some vortex regions in front of the crest, which are strong intermixing of this couple metals. The diffusion layer and melting layer are two typical layers at the interface. The diffusion layers are formed by strongly collision points, while the melting layers only appear on the stainless steel side. The average nanohardnesses of diffusion layer and melting layer are between that of copper and 304 stainless steel. The nanohardness of this couple metals exhibits increasing trend from 0° to 60°, while decreasing trend from 60° to 90°. The nanohardness in Area 4 of the vortex region is highest, where is the highest temperature. The average flexural strength of micro-cantilevers shows the same change rules with the nanohardness.

Entropy generation characteristics of phase change material in a variable wavy walled triplex tube latent heat storage unit for battery thermal management system

This study focuses on the thermal and frictional entropy generation characteristics of phase change material (PCM) in a triplex tube latent heat storage unit which is a promising technique for thermal management of lithium-ion batteries. Four different wavy structures for the triplex tube heat exchanger with variable waviness are considered, namely Case 1 to 4. Regarding the numerical analysis, the variations in mean temperature and liquid fraction of PCM are first revealed and presented where the crossflow heat transfer fluid in the system is considered water. Furthermore, thermal and frictional entropy generation rates in local and global means are separately discussed for both charging and discharging processes. The results showed that the difference in mean temperature and melting rates among the cases are more noticeable at the end of the process due to intensified natural convection, and Case 3 has 240 s (12.3%) shorter melting time compared to Case 1 and 4. Although solidification rates have similar trends in all cases, the solidification time is different, e.g., it is 110 s (5.2%) shorter in Case 4, compared to Case 1. The entropy generation trends are relatively similar during the solidification, while they are noticeably different in the melting process due to effect of liquid PCM flow.

Flow in Pillow-Plate Channels for High-Speed Turbomachinery Heat Exchangers

In numerous turbomachinery applications, e.g., in aero-engines with regenerators for improving specific fuel consumption (SFC), heat exchangers with low-pressure loss are required. Pil low-plate heat exchangers (PPHE) are a novel exchanger type and promising candidates for high-speed flow applications due to their smooth profiles avoiding blunt obstacles in the flow path. This work deals with the overall system behavior and gas dynamics of pillow-plate channels. A pillow-plate channel was placed in the test section of a blow-down wind tunnel working with dry air, and compressible flow phenomena were investigated utilizing conventional and focusing schlieren optics; furthermore, static and total pressure measurements were performed. The experiments supported the assumption that the system behavior can be described through a Fanno–Rayleigh flow model. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was able to cover important flow features within the channel. The effects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated, and a good qualitative agreement with theoretical and numerical predictions was found. The present analysis demonstrates that pressure losses in pillow-plate heat exchangers are rather low, although their strong turbulent mixing enables high convective heat transfer coefficients.

Chiral Photomechanical Behavior of Achiral Azobenzene-based Molecular Glass Particles Fixed in Agar Gel

Upon polarized laser beam irradiation, achiral azobenzene-based molecular glass particles changed their forms to wavy string-like structures in agar gel, and their ends were found to have helical structures with a left-handed rather than right-handed screw. Such chiral photomechanical behavior was suggested to be due to different dynamic viscoelasticity between clockwise and counterclockwise rotations of the surrounding agar gel, confirmed by the behavior of the gel sliding down in a glass tube.

Tunable isotropy on the mechanical properties of wavy hexachiral metamaterials: Numerical simulation and additive manufacturing

Hexachiral auxetic metamaterials can exhibit unconventional behaviors of negative Poisson’s ratio that can achieve superior mechanical properties including energy absorption and indentation resistance. The thickness ratio between the wavy ligament and center ring, which is denoted as [Formula: see text], has a critical influence on the isotropic mechanical properties of the hexachiral structures. This work aims to investigate the effect of [Formula: see text] on the isotropic auxeticity of wavy hexachiral structures under tensile and compressive loadings through simulations and experiments. A parametric study on hexachiral unit cells with [Formula: see text] values ranging from 0.25 to 1.5 was conducted with finite element analysis. With a decrease in [Formula: see text] values, the deformation mechanism showed improved coiling of the wavy hexachiral structure with thinner ligaments and thicker center rings, which exhibits better bending and rotational deformations, respectively. The wavy hexachiral structure with the [Formula: see text] value of 0.33 achieved the lowest average effective Poisson’s ratio of −0.94 and anisotropic factor of 0.00023. The tunable isotropic auxeticity is validated by the experimental Poisson’s ratios and deformations of the wavy hexachiral structures fabricated by laser additive manufacturing up to 3.33% tensile strain and 20% compressive strain. These findings provide insights on the design of mechanical isotropy of chiral metamaterials for additive manufacturing.

Interface microstructure and phase constitution of AA1060/TA2/SS30408 trimetallic composites fabricated by explosive welding

Multilayer metal composites based on dissimilar metals and alloys have great application value for many industries and key equipment because of excellent comprehensive properties. In this work, the AA1060/TA2/SS30408 trimetallic composites were successfully prepared by explosive welding technology. The 2D and 3D interface microstructure were characterized using field emission scanning electron microscope (FSEM) and computer tomography (CT). Meanwhile, to revel the phase constitution of two joining interfaces, the electron backscatter diffraction (EBSD) was carried out. It was concluded that both the Al/Ti and Ti/SS joining interfaces present typical wavy structures without obvious defects, an excellent bonding quality was confirmed. In addition, the 3D restructured interface morphologies indicated the characteristics looks like ripple and desert after the wind, which may be related to propagation direction of the impact wave. Furthermore, the phase constitution results show that the recrystallization and strong textures occurred at the two joining interfaces.

3D printed nanofiltration composite membranes with reduced concentration polarisation

3D printed nanofiltration (NF) composite membranes with surface patterns minimising the impact of concentration polarisation (CP) are presented here for the first time. The membranes consist of a NF polydopamine‐coated polyvinylidene fluoride (PVDF/PDA) selective layer on a 3D printed asymmetric wavy (patterned) support. The result is a wavy composite membrane with pure water permeance of 14 ± 2 LMH bar − 1 and molecular weight cut-off of ∼550 Da, measured using a crossflow NF setup at a transmembrane pressure of 2 bar for Reynold number ( Re ) of 700, using a range of dyes (mass balance >97% for all tests). The CP behaviour of the composite membranes was assessed by filtration of Congo red (CR) dye solution (0.01 g L − 1 ) , showing that the wavy pattern significantly reduced the impact of CP compared to the flat membranes, with a nearly tripling of the mass transfer coefficient and a 57% decline of the CP factor. Computational fluid dynamics showed that these significant performance improvements were due to improved hydrodynamics, with the maximum surface shear stress induced by the wavy structure (1.35 Pa) an order of magnitude higher than that of the flat membranes (0.18 Pa) at Re = 700. These results demonstrate that 3D printing is a viable technology route to reducing concentration polarisation in membrane nanofiltration applications. • Fabrication via 3D printing of NF composite membranes with surface wavy patterns. • Wavy composite membranes had a PWP of 14 ± 2 LMH bar − 1 and a MWCO of ∼550 Da. • Concentration polarisation was assessed by filtration of a Congo red solution. • The wavy structure led to a 57% lower CP and triple mass transfer coefficient. • Shear stress over the wavy structure is an order of magnitude higher than the flat one.

Fluid mechanics approach to analyzing collagen fiber organization.

.Significance: The spatial organization of collagen fibers has been used as a biomarker for assessing injury and disease progression. However, quantifying this organization for complex structures is challenging.Aim: To quantify and classify complex collagen fiber organizations.Approach: Using quantitative second-harmonic generation (SHG) microscopy, we show that collagen-fiber orientation can be viewed as pseudovector fields. Subsequently, we analyze them using fluid mechanic metrics, such as energy , enstrophy , and tortuosity .Results: We show that metrics used in fluid mechanics for analyzing fluid flow can be adapted to analyze complex collagen fiber organization. As examples, we consider SHG images of collagenous tissue for straight, wavy, and circular fiber structures.Conclusions: The results of this study show the utility of the chosen metrics to distinguish diverse and complex collagen organizations. We find that the distribution of values for and increases with collagen fiber disorganization, where they divide between low and high values corresponding to uniformly aligned fibers and disorganized collagen fibers, respectively. We also confirm that the values of cluster around 1 when the fibers are straight, and the range increases up to 1.5 when wavier fibers are present.

Properties of Magnetic Field Fluctuations in Long-Lasting Radial IMF Events from Wind Observation

Long-lasting radial interplanetary magnetic field (IMF) intervals in which IMF points along the solar wind velocity for several hours have many interesting properties. We investigate the average parameters and the behavior of magnetic field fluctuations within 419 such radial intervals. The power spectral density (PSD) calculated over 1-h intervals of a radial IMF is compared with PSDs in adjacent regions prior to and after the radial IMF. We concentrate on (1) the power of IMF fluctuations, (2) the median slopes of PSDs in both inertial and kinetic ranges, (3) the proton temperature and its anisotropy, and (4) the occurrence rate of wavy structures and their polarization. We have shown that the fluctuation amplitude is low in the radial IMF intervals in both magnetohydrodynamic (MHD) and kinetic ranges, and the spectral power increases with the cone angle in the MHD range. We discuss this effect in the light of present knowledge on plasma turbulence and peculiarities of observations of magnetic field variations under the radial background magnetic field. We found that in the radial IMF events, the proton temperature is more isotropic, the occurrence rate of waves is higher, and the waves have no preferred polarization in the frequency range from 0.1 to 1 Hz. It suggests that the radial IMF structure leads to a different development of turbulence than the typical Parker-spiral structure.

Noncoordinating-substituents-induced various Co and Ni coordination polymers with multiple pathways detection of Fe3+ and Cr(Ⅵ)

Six coordination polymers (CPs) based on a bis-pyridyl-bis-amide ligand containing thiophene, [Co(4-bmptd)(IPA)(H2O)] (1), [Co(4-bmptd)(5-HIP)(H2O)2]·2H2O (2), [Co(4-bmptd)(5-NIP)] (3), [Ni2(4-bmptd)2(IPA)2(H2O)2]·2H2O (4), [Ni(4-bmptd)(5-HIP)(H2O)2]·2H2O (5) and [Ni(4-bmptd)(5-NIP)] (6) [4-bmptd = N,N'-bis(4-methylenepyridyl)-2,5-thiophene dicarbonamide, H2IPA = isophthalic acid, 5-H2HIP = 5-hydroxyisophthalic acid, 5-H2NIP = 5-nitroisophthalic acid] were synthesized under hydrothermal conditions. CPs 1–6 were characterized by elemental analysis, IR and X-ray diffraction. CP 1 is a wavy 2D structure, CPs 2 and 5 are isostructural, showing the 2D interpenetrating structure. CPs 3 and 6 are isostructural, both of which are bilayer planar structures, while CP 4 is a planar 2D network. Taking CP 2 as an example, its fluorescence sensing properties for Fe3+ and Cr(VI) were studied. The carbon paste electrodes bulk-modified by CPs 1–4 were used as electrochemical sensors for the detection of Fe3+ and Cr(VI).

Novel lanthanide coordination polymers based on mixed N,O-donor ligands and their visible-light-driven photocatalytic performance

In the present work, we prepared three isostructural lanthanide (Ln) coordination polymers (CPs), namely [Ln (Hhpc) (phen) (NO3)] (Ln = Gd (1), La (2), Y (3), H3hpc = 5-hydroxy-1H-pyrazole-3-carboxylic acid, phen = 1,10-phenanthroline) by hydrothermal method. Their structures were characterized by single crystal X-ray diffraction, Fourier transform infrared spectrum, elemental analysis, powder X-ray diffraction and thermal gravimetric analysis. CPs 1–3 are isostrutural and exhibit two-dimensional (2D) wavy layered structure constructed from inorganic chains, in which equivalent eight coordinated Ln3+ ions are linked through carboxylate groups. The three dimensional supramolecular structure is further formed by hydrogen bonding. The photocatalytic experiments show that CPs 2 and 3 exhibit good photocatalytic performances under visible light in degradation of methylene blue organic dye. The photocatalytic degradation efficiencies in 90 min are about 86.19% and 93.60% for CPs 2 and 3, respectively. The photocatalytic degradation mechanisms have been proposed through photoelectrochemical and trapping radical experiments.

Capacitive Stretchable Strain Sensor With Low Hysteresis Based on Wavy-Shape Interdigitated Metal Electrodes

In this work, a stretchable thin film capacitive strain sensor based on wavy-structured interdigitated metal electrodes is successfully demonstrated. Wavy-shape metal electrodes were patterned using bulk silicon micromachining, endowing the electrodes with high stretchability and reliability. The electrodes were also protected with a layer of parylene C to prevent damage during stretching and embedded in polydimethylsiloxane (PDMS) stretchable package layers. The interdigitated electrodes sitting on the wavy structures experienced a waving angle change under external strain resulting in capacitive change, which is the sensing mechanism of the wavy structured interdigitated capacitive strain sensor (WICSS). The sensitivity and stretchability of the WICSS is dependent on the design of interdigitated electrodes and the dimension of the wavy structures. The gauge factor (GF) of the WICSS was 0.27 at 25% strain. There was little hysteresis during the stretching and releasing process in the range of 25% strain. The sensing property remained stable within a 1000 cycling test. The applications of the high-performance WICSS are also demonstrated by detecting the motion of human fingers and wrists.

Grain-size-dependent microstructure effects on cyclic deformation mechanisms in CoCrFeMnNi high-entropy-alloys

The effect of grain size on strain-controlled low-cycle fatigue (LCF) properties in the CoCrFeMnNi high-entropy alloys (HEAs) was investigated towards the distinct microstructural developments during cyclic loading at a strain amplitude of ± 1.0%. A much more prominent secondary cyclic hardening (SCH) behavior at the final deformation stage was observed in the fine-grained (FG, 18 µm) than in the coarse-grained (CG, 184 µm) CoCrFeMnNi. In-situ neutron-diffraction and microscopic examination, strongly corroborated by molecular dynamic (MD) simulations, indicated that dislocation activities from planar slip to wavy slip-driven subgrain structures within the grains acted as the primary cyclic-deformation behaviors in the FG CoCrFeMnNi. Differently observed in the cyclic behavior of the CG CoCrFeMnNi was due to a transition from the planar dislocation slip to twinning. Our findings suggested that the fatigue-resistant HEAs can be designed via tuning the microstructure with an optimal range of grain size at a specific strain amplitude.

Formation of Surface-Wrinkled Metal Nanosheets via Thermally Assisted Nanotransfer Printing

Nanopatterning methods for pattern formation of high-resolution nanostructures are essential for the fabrication of various electronic devices, including wearable displays, high-performance semiconductor devices, and smart biosensor systems. Among advanced nanopatterning methods, nanotransfer printing (nTP) has attracted considerable attention due to its process simplicity, low cost, and great pattern resolution. However, to diversify the pattern geometries for wide device applications, more effective and useful nTP based patterning methods must be developed. Here, we introduce a facile and practical nanofabrication method to obtain various three-dimensional (3D) ultra-thin metallic films via thermally assisted nTP (T-nTP). We show how to generate surface-wrinkled 3D nanostructures, such as angular line, concave-valley, and convex-hill structures. We also demonstrate the principle for effectively forming 3D nanosheets by T-nTP, using Si master molds with a low aspect ratio (A/R ≤ 1). In addition, we explain how to obtain a 3D wavy structure when using a mold with high A/R (≥ 3), based on the isotropic deposition process. We also produced a highly ordered 3D Au nanosheet on flexible PET over a large area (> 15 µm). We expect that this T-nTP approach using various Si mold shapes will be applied for the useful fabrication of various metal/oxide nanostructured devices with high surface area.

Fabrication and characterization of low-sheet-resistance and stable stretchable electrodes employing metal and metal nanowire hybrid structure

Stretchable electrodes with high stretching capability and low sheet resistance were developed using a metal/silver nanowires (AgNWs)/metal hybrid structure on a poly-dimethylsiloxane substrate. A low sheet resistance around 100 mΩ square−1 was achieved using the hybrid structures of Ag/AgNWs/Ag and Cu/AgNWs/Cu electrodes. The stretching capability under single and multi-cycling strain conditions was greatly improved due the AgNWs in-between top and bottom metal electrodes. The random connection of AgNWs generates new current path over the various cracks and wavy structures of the metal electrodes, which improve the initial resistance, the stretching capability under single strain up to 16%, and the resistance stability under 100 times cycling strain for the electrodes. Using a simple resistor model, it was shown that the hybrid structure is effective to improve the stretching capability of the stretchable metal electrodes due to the random connection of AgNWs in-between the metal electrodes.

Rubber linings for ball mills: New designs and production technologies

The current-level technologies of ore ball milling require novel understanding of the fill flow inside a mill, as well as the structure–lining material–process variables interaction. It is necessary to know: which physical phenomena cause wear of mill lining to evaluate the wear rate; which surface ensure milling; whether the flow is constant in time as the loading due to flow can both increase and decrease in the course of the mill rotation. The paper presents a new concept of the destruction mechanism of lining in drum mills, and on this basis, a wavy design of rubber lining is proposed. For the first time, the laboratory tests were carried out to determine the relative wear resistance of rubbers in the hydroabrasive environment. To select the parameters of rubber linings, the influence of the impact energy on the fracture resistance of the lining surface is investigated, and the mathematical relations to calculate coefficient of energy transfer to the metal structure of the machine are presented. The increased capacity of mills in terms of feed and finished size output with the Polymet wavy rubber linings is substantiated to be the result of the forced change in flow layers inside the mill over the work surface composed of elastic component (rubber) and rigid component (metal). The results of industrial tests of mills with the wavy structure of rubber linings with their work surface pregnant with balls or vulcanized metal inserts (Polymet) are presented. A promising technology with the use of screw extruders (syringes) for manufacturing of linings, dividing and discharge grids, sieves and other structurally complex products based on wear-resistant rubbers by filling molds under pressure has been proposed. This ensures high quality products without the need for increased material consumption per half-way product with direct molding technology.

Effect of orientation and heat input on behavior of solid-liquid interface boundary of phase change material in latent heat thermal energy storage container

The present study reports deals with experimental and numerical thermal analysis of solid - liquid (S-L) interface in order to characterize phase change material (PCM) used for energy storage of latent heat thermal energy system (LHTES). The two major aspects of the present work, both important in the field of LHTES, are to investigate the influence of the orientation of LHTES container and variable heat input. The experiments were carried out in a cylindrical chamber filled with paraffin wax. Camera recorded image of S-L interface is used to analyze the S-L interface position with respect to time during melting. Results will provide behavior of paraffin wax associated with the phase change process of PCM. Investigating the results leads to formulation of non-linear melting rate and a wavy structure with non-uniform profile of S-L interface boundary. The result shows evolution of convective motion being dominant and even responsible to generate this non- uniform shape of S-L interface.

Hydrothermal performance of single and hybrid nanofluids in Left-Right and Up-Down wavy microchannels using two-phase mixture approach

The aim of this study is to explore the hydrothermal attributes of three types of nanofluid containing the silver nanoparticles, aluminum oxide nanoparticles, and hybrid silver–aluminum oxide nanoparticles in two different types of microchannel, namely Left-Right and Up-Down wavy microchannels. The multi-phase mixture model is utilized to numerically simulate the flow at constant pumping powers. The results unmask that the secondary flow formed due to the wavy structure is more severe for the Left-Right wavy microchannel compared to the Up-Down one. Also, a maximum 330% enhancement in the convective heat transfer coefficient was observed for the Up-Down wavy microchannel working with the silver nanofluid, while the same value for the Left-Right one was 200%. Although the impact of using the nanofluids is more dominant for the Up-Down wavy microchannel, the Left-Right one exhibited better cooling performance in terms of the Nusselt number. It was observed that utilizing the nanofluids has minor impact on improving the bottom surface temperature uniformity for the Left-Right wavy microchannel, while for the Up-Down one this effect is more dominant. Lower amounts of thermal resistance were obtained in the case of using the nanofluids for both wavy structures, with more impact on the Up-Down one.