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Surface acoustic wave (SAW) technology has been extensively used in communications and sensing applications. This review summarizes the recent advancement of micro- and nanostructured sensing materials in enhancing the gas sensing performance of SAW devices.

Metal–organic framework (MOF)-derived metal oxide semiconductors have recently received extensive attention in gas sensing applications due to their high porosity and three-dimensional architecture.

Phase transition theory is a powerful approach to study shape-memory effect (SME) and dynamic relaxation behaviour in amorphous shape-memory polymers (SMPs) undergoing glass transition processes. However, previous studies are mostly limited to building-up of experimental models, mainly due to poor understanding of dynamic fluctuation of glass transition. In this study, the dynamic fluctuation of glass transition in the amorphous SMPs, whose thermodynamic SME is governed by the phase transition theory, was investigated using a shoving model. A constitutive relationship between potential energy and cooperatively rearranging region (CRR) volume is firstly developed to explore the working principle of phase transition in the thermodynamic SME of amorphous SMPs, based on the shoving model and Adam–Gibbs domain size model. The effect of CRR volume on the phase transition is further formulated using the strain function, and then employed to develop a constitutive stress–strain equation based on the extended Maxwell model. The working principles of cooperative SME and dynamic relaxation behaviours have been explored and discussed. Finally, the effectiveness of the analytical results obtained using the proposed model has been verified using the experimental results of amorphous SMPs reported in literature.

Extracellular vesicles (EVs) are secreted nanostructures that play various roles in critical cancer processes. They operate as an intercellular communication system, transferring complex sets of biomolecules from cell to cell. The concentration of EVs is difficult to decipher, and there is an unmet technological need for improved (faster, simpler, and gentler) approaches to isolate EVs from complex matrices. Herein, an acoustofluidic concentration of extracellular vesicles (ACEV) is presented, based on a thin‐film printed circuit board with interdigital electrodes mounted on a piezoelectric substrate. An angle of 120° is identified between the electrodes and the reference flat of the piezoelectric substrate for simultaneous generation of Rayleigh and shear horizontal waves. The dual waves create a complex acoustic field in a droplet, resulting in effective concentration of nanoparticles and EVs. The ACEV is able to concentrate 20 nm nanospheres within 105 s and four EV dilutions derived from the human prostate cancer (Du145) cell line in approximately 30 s. Cryo‐electron microscopy confirmed the preservation of EV integrity. The ACEV device holds great potential to revolutionize investigations of EVs. Its faster, simpler, and gentler approach to EV isolation and concentration can save time and effort in phenotypic and functional studies of EVs.

Droplet impact behaviour on a solid surface is critical for many industrial applications such as spray coating, food production, printing, and agriculture. For all these applications, a common challenge is to modify and control the impact regime and contact time of the droplets. This challenge becomes more critical for non-Newtonian liquids with complex rheology. In this research, we explored the impact dynamics of non-Newtonian liquids (by adding different concentrations of Xanthan into water) on superhydrophobic surfaces. Our experimental results show that by increasing the Xanthan concentration in water, the shapes of the bouncing droplet are dramatically altered, e.g., its shape at the separation moment is changed from a conventional vertical jetting into a “mushroom”-like one. As a result, the contact time of the non-Newtonian droplet could be reduced by up to50%. We compare the impact scenarios of Xanthan liquids with those of glycerol solutions having a similar apparent viscosity, and results show that the differences in the elongation viscosity induce different impact dynamics of the droplets. Finally, we show that by increasing the Weber number for all the liquids, the contact time is reduced and the maximum spreading radius is increased.

Understanding working principles and toughening mechanisms of soft elastomers has been a huge challenge due to their significant scaling effects from molecules to bulk polymer. In this study, by combining Sierpinski fractal and scaling theory, an extended Kelvin model is developed to investigate the mechanical behaviour of the soft elastomer undergoing scaled segment-chain-network. According to the scaling theory, a radial distribution function was initially introduced to explain the diffusion and relaxation behaviours of molecular segments with the Sierpinski fractal features. The self-consistent iteration of the Sierpinski fractal is then used to describe the scaling effects of segments and networks. Rubber elasticity of the polymer network is further formulated based on the self-consistent iteration equation and scaling theory. A constitutive stress–strain relationship is also derived to explore the toughness mechanism and working principle in the polymer elastomer. Finally, the effectiveness of the proposed model is verified using finite-element analysis and experimental results reported in the literature, to explore a scaling insight into toughening mechanisms of elastomers governed by the self-consistent Sierpinski iteration.

In this paper, we developed a sequential chemical etching and selenization processes to synthesize Co-MoSex double-shelled hollow nanocages (CMS DSHNCs) as high performance electrode materials for supercapacitor applications. Co-MoOx yolk-shelled hollow nanocages were firstly synthesized using a solvothermal process through facile ion-exchange reactions between zeolitic imidazolate framework-67 (ZIF-67) and MoO42- ions. By applying a solvothermal temperature of 160 oC in the presence of SeO32- and subsequently annealing strategy, CMS-DSHNCs were successfully synthesized with a yolk-shell hierarchically hollow and porous morphology of mixed metal selenides. The CMS-DSHNCs exhibit superior electrochemical properties as electrode materials for supercapacitor: e.g., a specific capacity of 1029.8 C g-1 at 2 A g-1 (3.089 C cm-2 at 6mA cm-2), a rate capability of ~76.14, a capacity retention at 50 A g-1, and a good cycle stability (95.2 capacity retention over 8000 cycles). A hybrid supercapacitor was constructed using the CMS-DSHNCs as the cathode and activated carbon (AC) as the anode in a solution of 3 M KOH, and achieved a high specific energy of 45 Wh kg−1, and a specific power up to 2222 W kg−1 with a good cycling stability of 94 after 8000 cycles.

The noble metal such as Pt has been used as the catalysts for hydrogen evolution reaction (HER), but with problems such as scarcity of resources and high cost. Anchoring transition metal atoms onto the catalysts is regarded as a potential approach to solve this problem and enhance the electrocatalytic performance of HER. For this purpose, two-dimensional materials, such as CuPS3 monolayer, are regarded as one of the most ideal carriers for adsorption of metal atoms. However, there is no previous study on this topic. In this paper, we systematically studied microstructures, electronic properties, and electrocatalytic performance of the CuPS3 monolayer anchored with transition metal atoms (e.g., Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) using a density functional theory (DFT). Results showed that all the transition metal atoms are favorably adsorbed onto the CuPS3 monolayer with large binding energies at the top of the Cu atom. The pristine CuPS3 monolayer has a large catalytic inertia for hydrogen evolution reactions, whereas after anchored with transition metal atoms, their catalytic performances have been significantly improved. The Gibbs free energy (ΔGH) is 0.44 eV for the H atom absorbed onto the pristine CuPS3 monolayer, whereas the ΔGH values for the V, Fe, and Ni atoms anchored onto the CuPS3 monolayer are 0.02, 0.11, and 0.09 eV, respectively, which is close to the ΔGH of H atom adsorbed on Pt (e.g., −0.09 eV). At the same time, the influence of hydrogen coverage rate was calculated. The result shows that V adsorbed on CuPS3 monolayer is catalytic active for HER for a large range of hydrogen coverage. Our results demonstrate that anchoring of V atom onto the CuPS3 monolayer is a potentially superior method for making the catalyst for the HER. Graphical abstract

Flexible surface acoustic wave (SAW) devices have recently attracted tremendous attention for their widespread application in sensing and microfluidics. However, for these applications, SAW devices often need to be bent into off-axis deformations between the acoustic wave propagation direction and bending direction. Currently, there are few studies on this topic, and the bending mechanisms during off-axis bending deformations have remained unexplored for multisensing applications. Herein, we fabricated aluminum nitride (AlN) flexible SAW devices by using high-quality AlN films deposited on flexible glass substrates and systematically investigated their complex deformation behaviors. A theoretical model was first developed using coupling wave equations and the boundary condition method to analyze the characteristics of the device with bending and off-axis deformation under elastic strains. The relationships between the frequency shifts of the SAW device and the bending strain and off-axis angle were obtained, and the results were identical to those from the theoretical calculations. Finally, we performed proof-of-concept demonstrations of its multisensing potential by monitoring human wrist movements at various off-axis angles and detecting UV light intensities on a curved surface, thus paving the way for the application of versatile flexible electronics.

Poor ductility of titanium matrix composites with medium/high-strength reinforced with carbonaceous nanomaterials (eg., graphene, carbon nanotubes etc.), has seriously restricted their wide-range engineering and practical industry utility. Herein, we propose a new methodology to significantly and simultaneously enhance both ductility and tensile strength of the titanium matrix composites. We ball milled Ti–6Al–4V (TC4) powders with in-situ chemically synthetized Ni decorated multi-walled carbon nanotubes (i.e MWCNTs@Ni), and then sintered the composites powders using spark plasma sintering (SPS). We achieved both a significant balanced between superior strength and increased ductility of the composite using the MWCNTs@Ni nanopowders. The enhanced strength in composites is mainly attributed to the interfacial structures for effectively enhanced load transfer capability between MWCNTs@Ni and Ti matrix, e.g., the formation of coherent/semi-coherent interfaces among interfacial phases Ti2Ni, TiC and Ti matrix. Furthermore, we applied the dislocation theory to reveal the toughening mechanisms of MWCNTs@Ni in the MWCNTs@Ni/TC4 composites. This study provides a new methodology of fabricating metal matrix composites (reinforced with carbon based nanomaterial) with both high strength and good ductility.

The multi-station direction finding and cross positioning method is often used in three-dimensional passive detection system when the measurement information only has DOA estimation value. However, the essence of this algorithm is to linearize the nonlinear problem, which is very vulnerable to the influence of direction finding error. In order to solve the above problem, the anti-interference virtual time reversal (VTR) algorithm combined with Tikhonov regularization total least squares (TLS) are for passive location. A multi-station passive location model is built and the cross antenna sensor array is used to receive signals. According to the established array model, the coordinate transformation formula of the observation station is derived and the coordinate formula of each array element is obtained by the transformation matrix, then the signal receiving model is established. The coordinates of virtual points are transformed for DOA estimation which accomplished by VTR, then the direction lines obtained. The results of the VTR direction finding are transformed into new space angles and the observation equations of the space angles are constructed. In order to overcome the influence of noise on the positioning solution, Tikhonov regularized TLS method is used to solve the equations for obtaining target position. The simulation results show that the algorithm can achieve high-resolution DOA estimation of the target at low SNR and the positioning errors under different number of observation stations are analyzed. The positioning accuracy has better performance compared with the unimproved least square method.

Polyampholyte (PA) hydrogels are incorporated of many internally charged polymer chains, which play an important role to influence the fractal networks and dynamic elasticity of the PA hydrogels owing to their different exchange and correlation charge-densities. Many properties of the PA hydrogels, such as mechanical strength and deformation, are significantly dependent on their fractal networks. However, working principles of chemo-mechanical coupling between the fractal networks and the elasticity of PA hydrogels have not been fully understood. In this study, a self-consistent fractal geometry model integrated with a complex function is proposed to understand the constitutive relationship between dynamic networks and tailorable mechanics in the PA hydrogels. The newly developed model is uniquely incorporated with the mechanochemistry, and describes the chemical polarization reactions of charged networks and their mechanical behaviors using complex fractal functions. Based on the rubber elasticity theory, constitutive stress–strain relationships of fractal networks have been described using their elastic, conformational, repulsive and polarization free-energy functions. Finally, effectiveness of the proposed model has been verified using both finite element analysis and experimental results of the PA hydrogels reported in literature.

‘What is the structure of water?’ This has been a perplexing question for a long time and water structure with various phases is a great topic of research interest. Topological complexity generally occurs because hydrophilic ions strongly influence the size and shape of condensed water structures owing to their kosmotropic and chaotropic transitions. In this study, an extended Stokes–Einstein model incorporating Flory–Huggins free energy equation is proposed to describe the constitutive relationship between dynamic diffusion and condensed water structure with a topological complexity. The newly developed model provides a geometrical strategy of end-to-end distance and explores the constitutive relationship between condensed ionic water structures and their dynamic diffusion behaviors. A free-energy function is then formulated to study thermodynamics in electrolyte aqueous solution, in which the condensed ionic water structures undergo topologically complex changes. Finally, effectiveness of the proposed model is verified using both molecular dynamics simulations and experimental results reported in literature.

Transparent microfluidic devices based on ZnO thin film/glass surface acoustic waves (SAWs) were explored for active surface cleaning based on its acoustofluidic performance. Acoustic waves generated from ZnO films on glass substrate were investigated and their acoustofluidic performance including transportation, jetting and nebulization were evaluated. Ash particles and starch solutions were used as model contaminants on the surface of the ZnO/glass SAW devices, and the mass loading of the contaminants on the device’s surface was monitored using the SAW device with a high sensitivity of 280.0 ± 9.0 Hz/(μg/mm2 ). Active surface cleaning of the contaminants was demonstrated based on the transportation of water droplets, and optimized SAW powers were identified which caused strong interactions between water droplet and contaminants, thus effectively cleaning the surfaces. Studies of surface heating effects induced by SAWs showed that the cleaning efficiency was also influenced by the substrate temperature induced by SAW agitations.

There are significant challenges in controlling uniformity of crystal inclination angles, growth orientations and film thicknesses to generate dual-mode surface acoustic waves (e.g., Rayleigh ones and shear-horizontal ones) for lab-on-a-chip applications. In this study, we demonstrate large area (up to three inches) and uniformly inclined piezoelectric ZnO films, sputtering-deposited on silicon using a glancing angle deposition method. Characterization using X-ray diffraction showed that the inclined ZnO films have an average crystal inclination angle of 29.0°, apart from the vertical (0002) orientation, at a substrate tilting angle of 30 o. Reflection signals of ZnO/Si surface acoustic wave devices clearly show the generations of both shear horizontal surface acoustic waves and Rayleigh waves. The Rayleigh waves enable efficient acoustofluidic functions including streaming and transportation of sessile droplets. Excitation direction of Rayleigh waves on the acoustofluidics versus the inclined angle direction has apparent influences on the acoustofluidic performance due to the anisotropic microstructures of the inclined films. The same device has been used to demonstrate biosensing of biotin/streptavidin interactions in a liquid environment using the shear-horizontal surface acoustic waves, to demonstrate its potential for integration into a complete lab-on-a-chip device.

The existence of bond exchange reactions and covalent adaptable networks (CANs) in thermoset epoxy has facilitated its self-healing and reversible mechanical capabilities. However, the toughening mechanisms and cooperative coupling of these crystal phases and CANs in a semi-crystalline thermoset epoxy have not been well understood. In this study, a Hamiltonian graph model is formulated to examine toughening mechanisms in the semi-crystalline thermoset epoxy based on the vertices and paths, both of which are employed to describe the crystalline phases and CANs, respectively. A free-energy equation is also developed based on the tail and tie free energy functions to investigate the cooperative coupling of crystal phases and CANs. The crystal phases increase the cross-linking density of the CANs, which helps the crystal phases with a homogeneous dispersion. Moreover, an extended Maxwell model is developed along with the Hamiltonian graph to explore the coupling effect of crystal phase and CAN on the mechanical behaviors of semi-crystalline thermoset epoxy. A constitutive stress–strain relationship is then proposed to describe the self-healing and toughening behaviors of semi-crystalline thermoset epoxy. The stress–strain relationship of semi-crystalline polymers, which incorporates crystal phases and CANs, has been thoroughly investigated using the analytical results obtained from the proposed Hamiltonian graph model. Finally, the effectiveness of the proposed model is verified using the finite element analysis method and a set of experimental data.

The electrically sensing characteristics of a liquid-crystal (LC)-infiltrated polarization-maintaining photonic crystal fiber (PCF) have been studied. The small holes on the end face of the fiber collapse and two large holes remain open by controlling discharging-time, -current, and -position of a fiber splicer, then LC is selectively infiltrated into the two large holes, which can not only save LC but also make the welding between the LC-infiltrated polarization-maintaining PCF and single-mode fiber much easier. A new method to weld the two fibers is proposed by filling and volatilizing ethanol to make LC a few millimeters away from the end face which can improve the sensing system stability and prevent the discharge of a fiber splicer from destroying LC molecules. A Sagnac interferometer is set up by embedding the LC-infiltrated polarization-maintaining PCF in a fiber loop and then its electroresponse characteristics are studied. The refractive-index distribution of the LC-infiltrated polarization-maintaining PCF varies with electric voltage due to the variable index of LC, which makes it possible to detect voltage. Three voltage ranges are discussed by the different dips and the sensitivity is improved with voltage increasing. The high sensitivity is up to 3.49 nm/V with the tuning range of 7 nm as voltage changes from 149.67 to 151.61 V. The Sagnac interferometer embedded with an LC-infiltrated polarization-maintaining PCF can be utilized as a voltage sensor, electro-optical modulator, or filter.

Due to the rapid development of modern communication technology and the substantial improvement of the processing capacity of communication equipment, it has become a challenging and meaningful research direction to realize the covert transmission of information by ensuring the low probability of detection (LPD) performance of the communication signals. The disadvantage of traditional fixed-parameter signal in LPD gradually appears. The paper proposes a time-varying chaotic multitone communication method to accomplish the LPD for the eavesdroppers. The method gets rid of the conventional LPD communication method whose performance improvement is exchanged at the expense of its reliability loss or sacrificing more resources. Based on the original chaotic multitone (CMT) communication method, the time-varying parameter is introduced to improve the randomness of the waveform and thus reduce the detection probability of eavesdroppers to the single tones in the multitone group (MTG). Meanwhile, to improve spectrum efficiency and reduce system complexity, the corresponding communication system model is designed based on orthogonal frequency division multiplexing (OFDM) technology. After given the corresponding detection and demodulation scheme based on the diversity and combination, the influence of time-varying parameters on the reliability for the cooperative receiver is analyzed. The LPD contribution of this method is evaluated by analyzing the detection probability of the eavesdropper. The experimental results show that the proposed method not only maintains the original reliability but also reduces the detection probability of eavesdroppers under the constant false alarm probability detection scheme.

In order to achieve fast and accurate passive location of the target radiation source, this paper puts forward a Virtual Time Reversal Method Based on Uniform Linear Array (ULA-VTR) passive location algorithm. This framework employs the passive time reversal focusing theory, which does not to require the physical transmission of time reversal signals and does not require pre-estimation of the channel to realize passive direction finding. The above principle is utilized to perform the target radiation source signal through a uniform linear sensor array for detection. The article provides the signal model of linear time reversal array and the virtual retransmission process in the first place. Then utilizes ULA-VTR to establish a dual-station passive location framework and derives the coordinate transformation equation to find its observation angle, in addition, establishes the observation equation system for obtaining the site of the target radiation source. Ultimately, the paper analyses the computational complexity of the ULA-VTR algorithm and adopts Geometric Dilution of Precision(GDOP) to discuss the positioning performance. The experimental results indicate that the technique presented in this paper has higher positioning accuracy under the low SNR compared with other techniques.

Surface acoustic wave (SAW) technology has been extensively explored for wireless communication, sensors, microfluidics, photonics, and quantum information processing. However, due to fabrication issues, the frequencies of SAW devices are typically limited to within a few gigahertz, which severely restricts their applications in 5G communication, precision sensing, photonics, and quantum control. To solve this critical problem, we propose a hybrid strategy that integrates a nanomanufacturing process (i.e., nanolithography) with a LiNbO3/SiO2/SiC heterostructure and successfully achieve a record-breaking frequency of about 44 GHz for SAW devices, in addition to large electromechanical coupling coefficients of up to 15.7%. We perform a theoretical analysis and identify the guided higher order wave modes generated on these slow-on-fast SAW platforms. To demonstrate the superior sensing performance of the proposed ultra-high-frequency SAW platforms, we perform micro-mass sensing and obtain an extremely high sensitivity of approximately 33151.9 MHz·mm2·μg−1, which is about 1011 times higher than that of a conventional quartz crystal microbalance (QCM) and about 4000 times higher than that of a conventional SAW device with a frequency of 978 MHz.

Using acoustofluidic channels formed by capillary bridges two models are developed to describe nodes formed from leaky and evanescent waves. The capillary bridge, formed between a microscope slide (waveguide) and a strip of polystyrene film (fluid guide) excludes solid-sidewall interactions in the channel. With this simplification, our experimental and numerical study showed that waves emitted from a single plane surface, interfere and form the nodes without any resonance in the fluid. Both models pay particular attention to the elements of the tensors normal to the solid-liquid interfaces, they find that the nodes form initially in the solid and then, antinodes in the stress emit waves into the fluid, replicating the pattern. In fluids with depths near half an acoustic wavelength most nodes are formed by leaky waves. In the glass, normal stress tensors reveal that water-loading reduces node-node separation and forms an overlay type waveguide which aligns the nodes predominantly along the channel. One new practical insight is that node separation can be controlled by water depth. In 0.2 mm deep channels (which are smaller than a ¼ wavelength) nodes from evanescent waves were realized. Here a suspension of yeast cells formed a pattern of small dot-like clumps of cells on the surface of the polystyrene film. We found the same pattern in the normal component of sound intensity in water near the polystyrene. The capillary bridge channel developed for this study is simple, low-cost, and could be developed for filtration, separation, or patterning of biological species in rapid immuno-sensing applications.

Cation substitution in spinel cobaltites (e.g., ACo2O4, in which A = Mn, Fe, Co, Ni, Cu, or Zn) is a promising strategy to precisely modulate their electronic structure/properties and thus improve the corresponding electrochemical performance for water splitting. However, the fundamental principles and mechanisms are not fully understood. This research aims to systematically investigate the effects of cation substitution in spinel cobaltites derived from mixed-metal-organic frameworks on the oxygen evolution reaction (OER). Among the obtained ACo2O4 catalysts, FeCo2O4 showed excellent OER performance with a current density of 10 mA·cm−2 at an overpotential of 164 mV in alkaline media. Both theoretical calculations and experimental results demonstrate that the Fe substitution in the crystal lattice of ACo2O4 can significantly accelerate charge transfer, thereby achieving enhanced electrochemical properties. The crystal field of spinel ACo2O4, which determines the valence states of cations A, is identified as the key factor to dictate the OER performance of these spinel cobaltites.

Flexible and stretchable strain sensors are vital for emerging fields of wearable and personal electronics, but it is a huge challenge for them to possess both wide-range measurement capability and good sensitivity. In this study, a highly stretchable strain sensor with a wide strain range and a good sensitivity is fabricated based on smart composites of carbon black (CB)/wrinkled Ecoflex. The sensor exhibits a maximum recoverable strain of up to 500% and a high gauge factor of 67.7. It has a low hysteresis, a fast signal response (as short as 120 ms), and a high reproducibility (up to 5000 cycles with a strain of 150%). The sensor is capable of detecting and capturing wide-range human activities, from speech recognition and pulse monitoring to vigorous motions. It is also applicable for real-time monitoring of robot movements and vehicle security crash in an anthropomorphic field. More importantly, the sensor is successfully used to send signals of a volunteer’s breathing data to a local hospital in real time through a big data cloud platform. This research provides the feasibility of using a strain sensor for wearable Internet of things and demonstrates its exciting prospect for healthcare applications.

Flexible electronic devices are normally based on organic polymer substrate. In this work, an ultrathin glass-based flexible, transparent, and ultrasensitive ZnO/glass surface acoustic wave (SAW) humidity sensor is developed using a composite sensing layer of ZnO nanowires (NWs) and graphene quantum dots (GQDs). It shows much larger effective electromechanical coupling coefficients and signal amplitudes, compared to those of flexible polymer-based SAW devices reported in the literature. Attributed to large specific surface areas of ZnO NWs, large numbers of hydrophilic functional groups of GQDs, as well as the formation of p-n heterojunctions between GQDs and ZnO NWs, the developed ZnO/glass flexible SAW sensor shows an ultrahigh humidity sensitivity of 40.16 kHz/% RH, along with its excellent stability and repeatability. This flexible and transparent SAW sensor has demonstrated insignificant deterioration of humidity sensing performance, when it is bent on a curved surface with a bending angle of 30°, revealing its potential applications for sensing on curved and complex surfaces. The humidity sensing and human breathing detection have further been demonstrated for wearable electronic applications using ultrathin glass-based devices with completely inorganic materials.

Droplet impact on arbitrary inclined surfaces is of great interest for applications such as antifreezing, self-cleaning, and anti-infection. Research has been focused on texturing the surfaces to alter the contact time and rebouncing angle upon droplet impact. In this paper, using propagating surface acoustic waves (SAWs) along the inclined surfaces, we present a novel technique to modify and control key droplet impact parameters, such as impact regime, contact time, and rebouncing direction. A high-fidelity finite volume method was developed to explore the mechanisms of droplet impact on the inclined surfaces assisted by SAWs. Numerical results revealed that applying SAWs modifies the energy budget inside the liquid medium, leading to different impact behaviors. We then systematically investigated the effects of inclination angle, droplet impact velocity, SAW propagation direction, and applied SAW power on the impact dynamics and showed that by using SAWs, droplet impact on the nontextured hydrophobic and inclined surface is effectively changed from deposition to complete rebound. Moreover, the maximum contact time reduction up to ∼50% can be achieved, along with an alteration of droplet spreading and movement along the inclined surfaces. Finally, we showed that the rebouncing angle along the inclined surface could be adjusted within a wide range.

In this paper, CuCr–Zr alloys prepared by vacuum melting with adding La and Ni elementswere heat-treated and aged, followed by plastic deformation using low-energy cyclic impact tests, to simultaneously improve their mechanical and electrical properties. Results showed that the grain size of the casted Cu–Cr–Zr alloys was significantly reduced after the solid-solution aging and plastic deformation process. There were a lot of dispersed Cr and Cu5Zr precipitates formed in the alloys, and the numbers of dislocations were significantly increased. Accordingly, the hardness was increased from 78 to 232 HV, and the tensile strength was increased from 225 to 691 MPa. Electrical conductivity has not been significantly affected after these processes. The enhancement of overall performance is mainly attributed to the combined effects of solid-solution hardening, fine grain hardening, and precipitation/dislocation strengthening.

For conventional titanium matrix composites (TiMCs), there is always a trade-off issue between enhanced strength and ductility of these materials. In this study, we explore a new design methodology by reinforcing titanium alloy matrix with carbonaceous nanomaterials and investigate the mechanisms for achieving a good balance of their strength and ductility. The TiMCs were synthesized through a low-cost powder metallurgy route using pre-mixed Ti-6Al-4V (TC4) powders and various carbon based nanofillers, including graphite powders (GPs), graphene oxide nanosheets (GONs) and graphene nanoplates (GNPs), and were further rolled at a temperature of 1173 K with a deformation of 66.7%. Among these three types of carbon reinforcing sources, the GNPs are more easily reacted with TC4 matrix and form more contents of TiC phases after sintering owing to their larger amounts of defects than those of the GPs and GONs. TiC products are identified to play a bridging role for not only connecting the TC4 matrix but also forming coherent interfaces with the TC4 matrix, thus facilitating a strong interfacial bonding of the composites. The as-rolled GNPs/TC4 composites exhibit a 0.2% yield strength of 1146.36 MPa (with an elongation of ∼8.1%), which is 24.6%, 9.22% and 5.62% higher than those of pure TC4, GPs/TC4 and GONs/TC4 composites. The GNPs/TC4 nanocomposites show a better balance of strength and ductility than those of the other two types of nanocomposites. The synergetic strengthening mechanisms are identified to be Orowan strengthening effect, effective load transfer capability of GNPs, and in-situ formation of interfacial TiC structures, which provide optimum interfacial microstructures to achieve good mechanical properties of the TiMCs.

Surface acoustic wave (SAW) devices are widely used for physical, chemical, and biological sensing applications, and their sensing mechanisms are generally based on frequency changes due to mass-loading effects at the acoustic wave propagation area between two interdigitated transducers (IDTs). In this paper, a new sensing mechanism has been proposed based on a significantly enhanced mass-loading effect generated directly on Au IDT electrodes, which enables significantly enhanced sensitivity, compared with that of conventional SAW devices. The fabricated ultrahigh-frequency SAW devices show a significant mass-loading effect on the electrodes. When the Au-electrode thickness increased from 12 to 25 nm, the Rayleigh mode resonant frequency decreased from 7.77 to 5.93 GHz, while that of the higher longitudinal leaky SAW decreased from 11.87 to 9.83 GHz. The corresponding mass sensitivity of 7309 MHz·mm2·μg–1 (Rayleigh mode) is ∼8.9 × 1011 times larger than that of a conventional quartz crystal balance (with a frequency of 5 MHz) and ∼1000 times higher than that of conventional SAW devices (with a frequency of 978 MHz). Trinitrotoluene concentration as low as 4.4 × 10–9 M (mol·L–1) can be detected using the fabricated SAW sensor, proving its giant mass-loading effect and ultrahigh sensitivity.

Nickel dichalcogenides have received extensive attention as promising noble-metal-free nanocatalysts for a hydrogen evolution reaction. Nonetheless, their catalytic performance is restricted by the sluggish reaction kinetics, limited exposed active sites, and poor conductivity. In this work, we report on an effective strategy to solve those problems by using an as-designed new porous-C/Ni2SeS nanocatalyst with the Ni2SeS nanostubs anchored on with porous-carbon skeletons process. On the basis of three advantages, as the enhancement of the intrinsic activity using the ternary sulfoselenide, increased number of exposed active sites due to the 3D hollow substrate, and increased conductivity caused by porous-carbon skeletons, the resulting porous-C/Ni2SeS requires an overpotential of only 121 mV at a current density of 10 mA cm–2 with a Tafel slope of 78 mV dec–1 for hydrogen evolution in acidic media and a good long-term stability. Density functional theory calculations also show that the Gibbs free energy of hydrogen adsorption of the Ni2SeS was −0.23 eV, which not only is close to the ideal value (0 eV) and Pt reference (−0.09 eV) but also is lower than those of NiS2 and NiSe2; large electrical states exist in the vicinity of the Fermi level, which further improves its electrocatalytic performance. This work provides new insights into the rational design of ternary dichalcogenides and hollow structure materials for practical applications in HER catalysis and energy fields.

The ability to actuate liquids remains a fundamental challenge in smart microsystems, such as those for soft robotics, where devices often need to conform to either natural or three-dimensional solid shapes, in various orientations. Here we propose a hierarchical nanotexturing of piezoelectric films as active microfluidic actuators, exploiting a unique combination of both topographical and chemical properties on flexible surfaces, whilst also introducing design concepts of shear hydrophobicity and tensile hydrophilicity. In doing so, we create nanostructured surfaces that are, at the same time, both slippery (low in-plane pinning) and sticky (high normal-to-plane liquid adhesion). By enabling fluid transportation on such arbitrarily shaped surfaces, we demonstrate efficient fluid motions on inclined, vertical, inverted, or even flexible geometries in three dimensions. Such surfaces can also be deformed and then reformed into their original shapes, thereby paving the way for advanced microfluidic applications.