Ionic Polymer Metal Composite Flapping Actuator Mimicking Dragonflies

In this study, variational principle is used for dynamic modeling of an Ionic Polymer Metal Composite (IPMC) flapping wing. The IPMC is an Electro-active Polymer (EAP) which is emerging as a useful smart material for `artificial muscle' applications. Dynamic characteristics of IPMC flapping wings having the same size as the actual wings of three different dragonfly species Aeshna Multicolor, Anax Parthenope Julius and Sympetrum Frequens are analyzed using numerical simulations. An unsteady aerodynamic model is used to obtain the aerodynamic forces. A comparative study of the performances of three IPMC flapping wings is conducted. Among the three species, it is found that thrust force produced by the IPMC flapping wing of the same size as Anax Parthenope Julius wing is maximum. Lift force produced by the IPMC wing of the same size as Sympetrum Frequens wing is maximum and the wing is suitable for low speed flight. The numerical results in this paper show that dragonfly inspired IPMC flapping wings are a viable contender for insect scale flapping wing micro air vehicles.     

Multimode Hydraulically Amplified Electrostatic Actuators for Wearable Haptics

The sense of touch is underused in today’s virtual reality systems due to lack of wearable, soft, mm-scale transducers to generate dynamic mechanical stimulus on the skin. Extremely thin actuators combining both high force and large displacement are a long-standing challenge in soft actuators. Sub-mm thick flexible hydraulically amplified electrostatic actuators are reported here, capable of both out-of-plane and in-plane motion, providing normal and shear forces to the user’s fingertip, hand, or arm. Each actuator consists of a fluid-filled cavity whose shell is made of a metalized polyester boundary and a central elastomer region. When a voltage is applied to the annular electrodes, the fluid is rapidly forced into the stretchable region, forming a raised bump. A 6 mm × 6 mm × 0.8 mm actuator weighs 90 mg, and generates forces of over 300 mN, out-of-plane displacements of 500 µm (over 60% strain), and lateral motion of 760 µm. Response time is below 5 ms, for a specific power of 100 W kg⁻¹. In user tests, human subjects distinguished normal and different 2-axis shear forces with over 80% accuracy. A flexible 5 × 5 array is demonstrated, integrated in a haptic sleeve.     

CTAB assisted immobilization of RuO2 nanoparticles on graphene oxide for electrochemical sensing of hydrazine

A novel method has been presented to modify glassy carbon electrode (GCE) with graphene oxide (GO) nanocomposite without introducing any electrode binder such as chitosan and Nafion. First, modify GCE with RuO₂ nanoparticles which have been dispersed in cetyltrimethyl ammonium bromide (CTAB) aqueous solution. Then, highly adhesive RuO₂/CTAB/GO nanocomposite membrane formed on GCE by immersing RuO₂/CTAB modified GCE in GO suspension. CTAB plays significant roles not only in the preparation of the nanocomposite but also in the immobilization of nanocomposite on GCE surface. First, CTAB was used as the dispersant of RuO₂ nanoparticles. Second, CTAB acted as the molecular linker to bind RuO₂ nanoparticles on graphene sheets. Third, CTAB formed CTAB/GO nanocomposite which is highly adhesive on the surface of electrodes such as GCE and ITO (indium tin oxide). The obtained RuO₂/CTAB/GO/GCE shows excellent electrocatalytic ability towards the oxidation of hydrazine. The oxidation of hydrazine on RuO₂/CTAB/GO/GCE is an adsorption-controlled process and the oxidation current is linear with the concentration of hydrazine in the range of 1 × 10^?5～1 × 10^?3 M with a detection limit of 2.3 × 10^?6 M. The application of this sensor in the sensing of hydrazine in real water samples confirmed its reliability and accuracy.     

Slit Tubes for Semisoft Pneumatic Actuators

This article describes a new principle for designing soft or ‘semisoft’ pneumatic actuators: SLiT (for SLit‐in‐Tube) actuators. Inflating an elastomeric balloon, when enclosed by an external shell (a material with higher Young's modulus) containing slits of different directions and lengths, produces a variety of motions, including bending, twisting, contraction, and elongation. The requisite pressure for actuation depends on the length of the slits, and this dependence allows sequential actuation by controlling the applied pressure. Different actuators can also be controlled using external “sliders” that act as reprogrammable “on‐off” switches. A pneumatic arm and a walker constructed from SLiT actuators demonstrate their ease of fabrication and the range of motions they can achieve.     

Interfacial characteristic of (Ba,Sr)TiO3 thin films deposited on different bottom electrodes

Barium strontium titanate (Ba_1?x Sr _x )TiO₃ (BST) thin films were deposited on Pt, Ru, RuO₂, and Pt/RuO₂ electrodes by radio frequency magnetron sputtering. The interfacial structure characteristic of the BST films deposited on various electrodes was investigated. X-ray photoelectron spectroscopy investigations showed that the interfacial diffusion layer in BST/Pt and BST/Ru are approximately 6 and 10 nm, respectively. The BST films are short of Ba and O elements comparing with the stoichiometry Ba_0.65Sr_0.35TiO₃ in the interface region. Dielectric measurement of the BST films with thickness ranging from 70 to 400 nm revealed that the BST films deposited on Pt and Pt/RuO₂ bottom electrodes have similar dielectric property, the BST films deposited on Ru have the highest bulk dielectric constant, and the thickness dependence of dielectric constant on the BST film deposited on RuO₂ electrode can be neglected. The interfacial layer dielectric constant of BST films deposited on Pt and Ru electrodes are estimated to be about 34.5 and 157.1, respectively. The effect of interfacial dead-layer on the dielectric constant could be eliminated through selecting appropriate bottom electrodes.     

Anisotropy of Young's Modulus of DD6 from 25 to 1200 °C Based on Nondestructive Dynamic Method

The Young's modulus is an essential factor for improving turbine blade design. The present study aims to obtain the flexural frequencies (f₁) and corresponding dynamic Young's modulus (E_d) of Ni-based single-crystal DD6 across a temperature range of 25–1200 °C using a nondestructive dynamic testing method. The relationship between the elastic constants and various crystal orientations is derived by employing the transformation of the elastic matrix. In addition, finite element (FE) simulation is conducted to calculate the flexural frequency (f₁) of the [001] crystal orientation. The findings indicate that the dynamic Young's modulus (E_d) decreases as the temperature increases within the range of 25–1200 °C. Furthermore, the E_d values for different crystal orientations follow the trend: E_d[1] < E_d[11] < E_d[111]. This suggests significant anisotropy in the material. The normalized model, matrix transformation calculation method, and finite element method demonstrate high accuracy in predicting the elastic modulus of DD6, as evidenced by the good correspondence between the fitting curves obtained using the normalization method and the test results. These results have practical applications in engineering, particularly in turbine blade design and other applications, and serve as valuable references for mechanical property testing and finite element simulations.     

Dynamic Young's modulus and glass transition temperature of selected tropical wood species

Abstract

Dynamic Young's modulus (E _d) of selected tropical wood species, namely Dyera polyphylla, Endospermum diadenum, Cratoxylum arborecens, Alstonia pneumatophora, Macaranga gigantea and Commersonia bartramia, used for the study was measured using the free–free flexural vibration method. Young's modulus from three point bending (E _3pb) and compression parallel to grain (E _cp) was also studied. The results show that the relationship between E _d and E _3pb for all wood species is very significant with the mean value of E _d consistently larger than or sometime equal to E _3pb. Surprisingly, the relationship between E _d and E _cp is not significant except for Alstonia pneumatophora. The dynamic mechanical thermal properties were also investigated using the dynamic mechanical thermal analyser (DMTA). The results showed that the storage modulus of the wood species at –90°C is in the range of 1·48–4·09 GPa with a glass transition temperature ranging from 50 to 70°C.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

‘Green’ composites Part 1: Characterization of flax fabric and glutaraldehyde modified soy protein concentrate composites

Fully biodegradable, environment friendly ‘green’ composites were prepared using glutaraldehyde (GA) modified soy protein concentrate (MSPC-G) and flax fabric. Soy protein concentrate (SPC) polymer has low tensile properties, poor moisture resistance and is brittle. SPC polymer with 15% glycerin, as an external plasticizer, exhibited fracture stress and Young's modulus of 17 and 368 MPa, respectively. SPC polymer was cross-linked with GA to increase its tensile properties and improve its processability as a resin to manufacture flax fabric-reinforced composites. GA reacts with the free amine groups in SPC to form crosslinks. MSPC-G showed 20% increase in fracture stress and 35% increase in Young's modulus as well as improved moisture resistance compared to SPC. Besides the mechanical properties, MSPC-G was also characterized for its thermal stability and dynamic mechanical properties.Composite laminates, approximately 1 mm thick, were made using flax fabric and MSPC-G polymer. Composite specimens were prepared with two different orientations, namely, 0° or 90°. The laminates exhibited a Young's modulus of 1.01 and 1.26 GPa in the longitudinal and transverse directions, respectively. The experimental values were compared with the theoretical predictions using pcGINA^© software and showed good agreement. The composite specimens also showed good adhesion between flax fabric and MSPC-G resin.     

Young's modulus of Fe-, Co-, Pd- and Pt-based amorphous wires produced by the in-rotating-water spinning method

This paper presents the Young's modulus of Fe_100?x?y Si _x B _y , Fe_100?x?y P _x C _y , Co_100?x?y Si _x B _y , Pd_77.5Cu₆Si_16.5, Pd₄₈Ni₃₂P₂₀ and Pt₆₀Ni₁₅P₂₅ amorphous wires determined from the Young's modulus sound velocity measurement. With increasing metalloid content, the Young's modulus increases from 1.58×10¹¹ to 1.87×10¹¹ N m^?2 for Fe-Si-B, from 1.40×10¹¹ to 1.52×10¹¹ N m^?2 for Fe-P-C and from 1.73×10¹¹ to 1.75×10¹¹ N m^?2 for Co-Si-B systems. The increase in Young's modulus with the amount of metalloid elements is the largest for B, followed by Si, C and then P. The Young's modulus of Fe- and Co-Si-B amorphous wires increases significantly with the replacement of iron or cobalt by IV–VII group transition metals. It was recognized that there existed a strong correlation between Young's modulus (E) and tensile fracture strength (σ _f); the ratio of σ _f to E is approximated to be 0.02 for all the amorphous wires investigated. These results imply that the Young's modulus is dominated mainly by the structural and compositional short-range orderings due to the strong interaction between metal and metalloid atoms which hinders the internal displacements. The existence of a constant ratio for σ _f/E was interpreted to originate from a common mechanism for plastic flow of the amorphous wires. Further, it was noted that the Young's modulus of the Fe- and Co-based amorphous wires with diameters of ? 100 to 120 Μm was slightly lower than that of the amorphous ribbons with thicknesses of ? 20 to 25 Μm. This difference was attributed to the difference in structural ordering due to the differences in the solidification processes.     

Three‐Dimensional Printing of Complex‐Shaped Alumina/Glass Composites

Alumina/glass composites were fabricated by three‐dimensional printing (3DP?) and pressureless infiltration of lanthanum‐alumino‐silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600 °C for 2 h prior to glass infiltration at 1100 °C for 2 h. The influence of layer thickness and sample orientation within the building chamber of the 3D‐printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150 µm resulted in an increase of the total porosity from ～19 to ～39 vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y‐axis of the 3D‐printer compared to those orientated along the X‐ or the Z‐axis, respectively. Fabricated Al₂O₃/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6 MPa m^1/2, 175 MPa, 228 GPa, and 12 GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process.     

Hierarchically Arranged Helical Fiber Actuators Derived from Commercial Cloth

The first hygroscopically tunable cloth actuator is realized via impregnation of a commercial cloth template by a three dimensionally (3D) nanoporous polymer/carbon nanotube hybrid network. The nanoporous hybrid guarantees diffusion of water into the cloth actuator and amplifies the deformation scale. The cloth actuators are mechanically stable with high tensile strength. Because the commercial cotton cloth is inexpensive, such actuators capable of complex motions can be produced in a large size and scale for a wide variety of utilities (e.g. electric generators and “smart” materials).     

Combinatorial screening of halide perovskite thin films and solar cells by mask-defined IR laser molecular beam epitaxy

Abstract

As an extension of combinatorial molecular layer epitaxy via ablation of perovskite oxides by a pulsed excimer laser, we have developed a laser molecular beam epitaxy (MBE) system for parallel integration of nano-scaled thin films of organic–inorganic hybrid materials. A pulsed infrared (IR) semiconductor laser was adopted for thermal evaporation of organic halide (A-site: CH₃NH₃I) and inorganic halide (B-site: PbI₂) powder targets to deposit repeated A/B bilayer films where the thickness of each layer was controlled on molecular layer scale by programming the evaporation IR laser pulse number, length, or power. The layer thickness was monitored with an in situ quartz crystal microbalance and calibrated against ex situ stylus profilometer measurements. A computer-controlled movable mask system enabled the deposition of combinatorial thin film libraries, where each library contains a vertically homogeneous film with spatially programmable A- and B-layer thicknesses. On the composition gradient film, a hole transport Spiro-OMeTAD layer was spin-coated and dried followed by the vacuum evaporation of Ag electrodes to form the solar cell. The preliminary cell performance was evaluated by measuring I-V characteristics at seven different positions on the 12.5 mm × 12.5 mm combinatorial library sample with seven 2 mm × 4 mm slits under a solar simulator irradiation. The combinatorial solar cell library clearly demonstrated that the energy conversion efficiency sharply changes from nearly zero to 10.2% as a function of the illumination area in the library. The exploration of deposition parameters for obtaining optimum performance could thus be greatly accelerated. Since the thickness ratio of PbI₂ and CH₃NH₃I can be freely chosen along the shadow mask movement, these experiments show the potential of this system for high-throughput screening of optimum chemical composition in the binary film library and application to halide perovskite solar cell.     

High‐Performance Hierarchical Black‐Phosphorous‐Based Soft Electrochemical Actuators in Bioinspired Applications

Bioinspired methods allowing artificial actuators to perform controllably are potentially important for various principles and may offer fundamental insight into chemistry and engineering. To date, the main challenges persist regarding the achievement of large deformation in fast response‐time and potential‐engineering applications in which electrode materials and structures limit ion diffusion and accumulation processes. Herein, a novel electrochemical actuator is developed that presents both higher electromechanical performances and biomimetic applications based on hierachically structured covalently bridged black phosphorous/carbon nanotubes. The new actuator demonstrates astonishing actuation properties, including low power consumption/strain (0.04 W cm^?2 %^?1), a large peak‐to‐peak strain (1.67%), a controlled frequency response (0.1–20 Hz), faster strain and stress rates (11.57% s^?1; 28.48 MPa s^?1), high power (29.11 kW m^?3), and energy (8.48 kJ m^?3) densities, and excellent cycling stability (500 000 cycles). More importantly, bioinspired applications such as artificial‐claw, wings‐vibrating, bionic‐flower, and hand actuators have been realized. The key to high performances stems from hierachically structured materials with an ordered lamellar structure, large redox activity, and electrochemical capacitance (321.4 F g^?1) for ions with smooth diffusion and flooding accommodation, which will guide substantial progress of next‐generation electrochemical actuators.     

A Methodology for Accurately Measuring Mechanical Properties on the Micro‐Scale

Abstract: A methodology has been developed for accurately measuring the mechanical properties of materials used on the micro‐scale. The direct tension test method using a dog bone‐type specimen has been employed, as it is the most effective and straightforward method to obtain results including a full stress–strain curve. The goal of this investigation was to develop a universal, yet simple and reliable, methodology to be used for accurate characterisation of mechanical properties for a wide variety of materials. Specimens from single crystal silicon were fabricated using photolithography by means of deep reactive ion etching. This material was chosen as it is expected that on both the micro‐ and macro‐scales, Young's modulus will have the same value. Hence, the accuracy of the methodology may be unambiguously examined. The test set‐up includes a small test machine containing a load cell whose maximum capacity is 5 N and is capable of direct gripping and displacement control. The specimens were found to have a trapezoidal cross‐section that was accurately measured using a scanning electron microscope. The strains were obtained by means of digital image correlation using images obtained via optical microscopy. The quantities measured include Young's modulus E, the fracture strength σ_f and the fracture strain ε_f. The average value of E obtained in the micro‐tests agrees well with the reference value obtained on the macro‐scale.     

Y3−xErxAl5O12 Aluminate Ceramics: Preparation,Thermal Properties and Theoretical Model of Thermal Conductivity

Rare‐earth aluminate ceramics for thermal‐barrier coatings (TBCs) are synthesized. The Young's modulus and thermal properties decrease with erbium additive increasing. The Y_3?xEr_xAl₅O₁₂ ceramics (x = 1, 3) possess a much‐lower thermal conductivity compared with 8YSZ. The lower Young's modulus and thermal‐expansion coefficient are due to the larger atomic weight of the Er substitutional atom. Additional phonon‐scattering effects also contribute to the lower thermal conductivity. The results indicate that Y_3?xEr_xAl₅O₁₂ can be explored as a candidate material for TBC systems. A theoretical model that describes the influence of point defects on the thermal conductivity is discussed.     

Electroactive Ionic Soft Actuators with Monolithically Integrated Gold Nanocomposite Electrodes

Electroactive ionic gel/metal nanocomposites are produced by implanting supersonically accelerated neutral gold nanoparticles into a novel chemically crosslinked ion conductive soft polymer. The ionic gel consists of chemically crosslinked poly(acrylic acid) and polyacrylonitrile networks, blended with halloysite nanoclays and imidazolium‐based ionic liquid. The material exhibits mechanical properties similar to that of elastomers (Young's modulus ≈ 0.35 MPa) together with high ionic conductivity. The fabrication of thin (≈100 nm thick) nanostructured compliant electrodes by means of supersonic cluster beam implantation (SCBI) does not significantly alter the mechanical properties of the soft polymer and provides controlled electrical properties and large surface area for ions storage. SCBI is cost effective and suitable for the scaleup manufacturing of electroactive soft actuators. This study reports the high‐strain electromechanical actuation performance of the novel ionic gel/metal nanocomposites in a low‐voltage regime (from 0.1 to 5 V), with long‐term stability up to 76 000 cycles with no electrode delamination or deterioration. The observed behavior is due to both the intrinsic features of the ionic gel (elasticity and ionic transport capability) and the electrical and morphological features of the electrodes, providing low specific resistance (<100 Ω cm^?2), high electrochemical capacitance (≈mF g^?1), and minimal mechanical stress at the polymer/metal composite interface upon deformation.     

Growth and characterization of RuO2 single crystals

Using the vapor transport technique in a flowing oxygen system, we have grown the largest single crystals of RuO₂ ever reported (10 mm × 5 mm × 5 mm). Polycrystalline RuO₂, a mixture of polycrystalline RuO₂ and purified Ru metal powder, or purified Ru metal powder were used as the starting material. Optimum conditions are given for growing large high quality crystals. The morphology, stoichiometry and resistivity of selected single crystals of RuO₂ are discussed.     

Compressive behaviour of open cell Al–Al2O3 composite foams fabricated by sintering and dissolution process

Abstract

The sintering and dissolution process (SDP) was used to produce the fine open cell Al–Al₂O₃ composite and pure Al foams with the relative density of 0·25–0·40 and the pore size of 112–400 μm. The composite foam exhibited much higher yield strength and Young's modulus than the pure Al foam, and thus had an elevated plateau stress. Moreover, the composite foam showed a unique dependence of the compression stress on the pore size, i.e. it increased with increasing pore size, which was quite different from that for the common metal foams.     

Pt–Ru alloy electrode for(Ba,Sr)TiO3 capacitor

The Pt–Ru alloy was evaluated as a bottom electrode material in the (Ba,Sr)TiO₃ (BST) capacitor. Surface oxidation producing the RuO₂ layer for Pt–Ru(50 at %) first occurred and then BST film was deposited in the BST sputtering process. The thickness of RuO₂ formed from oxidation by an oxidant gas for BST formation, was thicker for the higher substrate temperature and the RuO₂ film shows the (1 0 1) orientation. The RuO₂ film between BST and Pt–Ru(50 at %) may block the diffusion of oxygen through the bottom electrode. The BST film deposited on Pt–Ru(50 at %) has a rough surface and a stronger intensity of (1 1 0) than that on Pt.