Mismatch Strain Research Articles

Texture in atomic layer deposited Hf0.5Zr0.5O2 ferroelectric thin films

HfO2-based ferroelectric materials have excellent CMOS compatibility and polarization even in ultrathin films, which is regarded as promising candidate material for memory devices and related electronic devices. However, as the ferroelectric layer thickness scaling down, the consistency of device performance is inevitably affected by the complex polyphase and polycrystalline nature of HfO2-based ferroelectric thin films. Therefore, obtaining and controlling the texture of HfO2-based ferroelectric thin films is extremely important for regulating polarization orientation and improving ferroelectric polarization. In this work, 10 nm Hf0.5Zr0.5O2 (HZO) films were prepared by atomic layer deposition (ALD) on Nb-doped SrTiO3 (NSTO) single crystal substrates. The texture and orientation of HZO films were analyzed through the state-of-the-art spherical aberration corrected transmission electron microscope (Cs-TEM) technique. The domain matching epitaxy between HZO films and NSTO substrate helps eliminate lattice mismatch and residual misfit strain, and ultimately leads to the formation of <112> texture in HZO ferroelectric films. The obtained results represent lattice and interface play an extremely important role in regulating the ferroelectricity of HfO2-based films, which provides a way to design ultra-thin HfO2-based materials with excellent ferroelectric polarization by controlling the crystal structure and orientation.

Rapid Design of Fully Soft Deployable Structures Via Kirigami Cuts and Active Learning

AbstractSoft deployable structures – unlike conventional piecewise rigid deployables based on hinges and springs – can assume intricate 3‐D shapes, thereby enabling transformative soft robotic and manufacturing technologies. Their virtually infinite degrees of freedom allow precise control over the final shape. The same enabling high dimensionality, however, poses a challenge for solving the inverse problem: fabrication of desired 3D structures requires manufacturing technologies with extensive local actuation and control, and a trial‐and‐error search over a large design space. Both of these shortcomings are addressed by first developing a simplified planar fabrication approach that combines two ingredients: strain mismatch between two layers of a composite shell and kirigami cuts that relieves localized stress. In principle, it is possible to generate targeted 3‐D shapes by designing the appropriate kirigami cuts and the amount of prestretch (without any local control). Second, a data‐driven physics‐guided framework is formulated that reduces the dimensionality of the inverse design problem using autoencoders and efficiently searches through the “latent” parameter space in an active learning approach. The rapid design procedure is demonstrated via a range of target shapes, such as peanuts, pringles, flowers, and pyramids. Experiments and our numerical predictions are found to be in good agreement.

Cellulose nanocrystals-gelatin composite hydrocolloids: Application to controllable responsive deformation during 3D printing

Three-dimensional (3D) food printing is an effective technology for creating food designs with complex appearances and customized nutritional profiles. However, controlling the deformation of 3D printed foods during processing remains a challenge. Here, a food hydrocolloid with customizable designs during heating and dehydration was designed using cellulose nanocrystals (CNC) and gelatin (G). The resultant cellulose nanocrystals-gelatin (CNC-G) hydrocolloid exhibited favorable rheological characteristics for three-dimensional (3D) printing. 3D printing allows the controlled oriented alignment of the CNC particles within the hydrocolloid along the printing direction, endowing the CNC-G hydrocolloid with highly anisotropic structures. This anisotropic property can cause a strain mismatch during dehydrated food processing, leading to a specific deformation of the hydrocolloid. By adjusting the 3D printing parameters and intentionally designing of the 3D printed structures, the alignment degree of CNCs within the hydrocolloid can be controlled, and thus, its deformation can be programmed. The customizable deformation of CNC-G hydrocolloid during food processing was deliberately designed through printing, and its adaptability and flexibility are demonstrated through the "flapping" of a butterfly and the "blooming" of a four-leaf clover. The flexibility and customizability of CNC-G hydrocolloid in 3D printing provide a new strategy to achieve deformation and precise control of 3D printed foods during processing.

Highly Efficient Fabrication of Biomimetic Nanoscaled Tendrils for High-Performance PM0.3 Air Filters.

Particulate matter pollution has become a serious public health issue, especially with the outbreak of new infectious diseases. However, most existing air filtration materials face challenges such as being too bulky, having high resistance, and a trade-off between filtration efficiency and air permeability. Here, a unique electro-blown spinning technique is used to prepare an air filter made of biomimetic nanoscaled tendril nonwovens (Nano-TN). The introduction of an airflow field significantly increases the whipping frequency and the strain mismatch of composite jets, achieving large-scale and highly efficient preparation of Nano-TN. The resultant Nano-TN has an ultrahigh porosity (97%) and a small pore size (2.9 μm). At the same filtration level, its air resistance is 37% lower than that of traditional straight nanofibrous nonwovens and has a higher dust-holding capacity. Moreover, compared with traditional three-dimensional air filters, the Nano-TN filter is thinner, offering tremendous application prospects in various environmental purification and personal protection fields.

Effects of size mismatch of halide ions on the phase stability of mixed halide perovskites

The phase stability of mixed halide perovskites plays a vital role in the performance and reliability of perovskite-based devices and systems. In this work, we incorporate the contribution of the strain energy due to the size mismatch of halideions in Gibbs free energy for the analysis of the phase stability of mixed halide perovskites. Analytical expressions of the chemical potentials of halide ions in mixed halide perovskites are derived and used to determine the critical atomic fractions of halide ions for the presence of spinodal decomposition (phase instability). The numerical analysis of CH3NH3PbI x Br3-x mixed halide perovskite reveals the important role of the mismatch strain from halide ions in controlling the phase instability of mixed halide perovskite, i.e., increasing the mismatch strain widens the range of x for the phase separation of mixed halide perovskites. To mitigate the phase instability associated with the strain energy from intrinsic size mismatch and/or light-induced expansion, strain and/or field engineering, such as high pressure, can be likely applied to introduce strain and/or field gradient to counterbalance the strain gradient by the mismatch strain and/or light-induced expansion.

Adhesion properties of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2 &lt;/sub&gt;interface: Size and temperature effects

The interface adhesion properties are crucial for designing and fabricating two-dimensional materials and related nanoelectronic and nanomechanical devices. Although some progress of the interface adhesion properties of two-dimensional materials has been made, the underlying mechanism behind the size and temperature dependence of interface adhesion energy and related physical properties from the perspective of atomistic origin remain unclear. In this work, we investigate the effects of size and temperature on the thermal expansion coefficient and Young’s modulus of MoS&lt;sub&gt;2&lt;/sub&gt; as well as interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; based on the atomic-bond-relaxation approach and continuum medium mechanics. It is found that the thermal expansion coefficient of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; is significantly larger than that of its few-layer and bulk counterparts under the condition of ambient temperature due to size effect and its influence on Debye temperature, whereas the thermal expansion coefficient increases with temperature going up and almost tends to a constant as the temperature approaches the Debye temperature. Moreover, the variations of bond identity induced by size effect and temperature effect will change the mechanical properties of MoS&lt;sub&gt;2&lt;/sub&gt;. When the temperature is fixed, the Young’s modulus of MoS&lt;sub&gt;2&lt;/sub&gt; increases with size decreasing. However, the thermal strain induces the volume expansion, resulting in the Young’s modulus of MoS&lt;sub&gt;2&lt;/sub&gt; decreasing. Furthermore, the size and temperature dependence of lattice strain, mismatch strain of interface, and Young’s modulus will lead the van der Waals interaction energy and elastic strain energy to change, resulting in the change of interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt;. Noticeably, the interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; gradually increases with MoS&lt;sub&gt;2&lt;/sub&gt; size decreasing, while the thermal strain induced by temperature causes interface adhesion energy of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; to decrease with temperature increasing. In addition, we predict the conditions of the interface separation of MoS&lt;sub&gt;2&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; under different sizes and temperatures. Our results demonstrate that increasing both size and temperature can significantly reduce the interface adhesion energy, which is of great benefit in detaching MoS&lt;sub&gt;2&lt;/sub&gt; film from the substrate. Therefore, the proposed theory not only clarifies the physical mechanism regarding the interface adhesion properties of transition metal dichalcogenides (TMDs) membranes, but also provides an effective way to design TMDs-based nanodevices for desirable applications.

Residual Stress Map for 75Ni13.5Cr2.7B-3.5Si Clad 316 Stainless Steel

Plasma Transfer Arc (PTA) process uses the intense heat of electric arc to melt and fuse the 75Ni13.5Cr2.7B-3.5Si hard-facing alloy and the base metal. This process develops substantial residual stresses near the hard-faced surfaces during deposition and subsequent solidification and cool down. Furthermore, when a material interface is present, additional residual stress is formed because of the thermal strain mismatch of the dissimilar materials caused by their different thermal expansion coefficients. These stresses can cause cracks in the overlay during the component’s service life or even earlier during manufacturing which can lead to partial or total loss of the part structural integrity. To start optimizing the process to avoid these defects, it is necessary to know the residual stress distribution in the part and how it is related to the process parameters. Hard-faced components are having distinct microstructures with a step change in material properties, and this makes the residual stress measurement more challenging. This paper presents 2D residual stress maps of the deposit cross sections for PTA hard-faced samples using the contour method. This study is part of an ongoing research on the influence of process parameters on the residual stress and local microstructure of 75Ni13.5Cr2.7B-3.5Si clad 316 stainless steel.

(Invited) Modelling and Experiments to Guide Scale-up of Structured Electrode Manufacturing for Fast-Charging and Long-Life Li-Ion Cells

For widespread adoption of electric vehicles, lithium-ion batteries (LiBs) need to achieve energy densities of around 350 Wh/kg, cost less than $100/Wh, and be able to charge quickly within around 15 minutes. To achieve this aim, the material properties of lithium-ion electrodes need to be optimized across multiple length scales, from particle to cell. Leveraging advanced characterization techniques to acquire representative particle- and electrode-level microstructures, we develop models to simulate the behavior of individual particles and novel electrode architectures that are feasible to synthesize and scale up to manufacture high performance batteries. We then demonstrate manufacturing of the novel electrode architectures at pilot scale roll-to-roll processing using high-speed laser-ablation to tune the electrode architecture. Guided by multi-scale models, we observe substantial improvements in cell performance.For the particle level optimization, the primary objective is to develop a predictive cathode-particle cracking model that captures secondary-particle fracture dynamics, relate damage to observed capacity fade, and provide design criteria for future cathode development. The novel coupled electrochemistry-transport-mechanics model is implemented on realistic three-dimensional LiNixMnyCozO2 (NMC) secondary particles. Realistic secondary particles are generated using statistically representative particle generation software. The generated particle architecture is used in chemo-mechanical models to simulate Li (de)intercalation during cycling. The model considers diffusion-induced stress, mismatch strain, and damage evolution coupled through the spatial and temporal evolution of geometric, transport, and mechanical properties. Contrary to most cathode-cracking models, instead of a cohesive-zone implementation, a continuum-damage model is used. Additionally, the model simulates several realistic secondary particle geometries to study the effect of secondary-particle size and grain size on damage. The model is expected to provide insights into ideal cathode geometries (e.g., grain morphology, orientation, and particle sizes) and optimal cathode-sensitive charge-protocol development.For electrode level optimization, structuring the electrode with channels to provide straight diffusion paths along the electrode thickness is a promising approach with demonstrated improved capacity retention at fast charge. The optimal shape and spatial distribution of these channels, that together form the so-called Secondary Pore Network (SPN), taking into consideration the manufacturing technique limitations, is however still unknown. Battery manufacturing cost is another key limiting factor for the wide adoption of electric vehicles. The electrolyte wetting process is an expensive step as complete infiltration can takes days, thus requiring expensive storage space and time. Structured electrodes have also demonstrated reduced wetting time as channels offer highways indifferently for capillary-driven or concentration gradient-driven transport mechanisms. However, the optimal channel pattern for enhanced wetting is also unknown. In this work, we identify both optimal patterns, for fast charging, and for fast wetting, independently, through use of a genetic algorithm (GA). The final proposed structured electrode is therefore the baseline porous matrix, a Secondary Pore Network (SPN) tailored for fast charging, and a Tertiary Pore Network (TPN) tailored for fast wetting, with less than 10% of active material removed in total.High-speed laser-ablation is applied to manufacturing this electrode architecture. Laser ablation is a scalable technique for decreasing the effective tortuosity of electrodes by selectively removing material with high precision. Applied to thick electrode coatings, this work focuses on understanding the impact of laser ablation on electrode material properties at the beginning of life and synergistic impacts of ablated channels on cell performance throughout their cycle life. Post laser ablation, local changes in chemistry, crystallography, and morphology of the laser-impacted electrode regions are investigated. It is shown that femtosecond pulsed laser ablation can achieve high-rate material removal with minor material damage locally at the interface of the impacted zones. The capacity achieved during a 6C (10 min) constant-current constant-voltage charge to 4.2 V improved from 1 mAh cm−2 for the non-ablated electrodes to almost 2 mAh cm−2 for the ablated electrodes. This benefit is attributed to a synergistic effect of enhanced wetting and decreased electrode tortuosity. The benefit was maintained for over 120 cycles, and upon disassembly decreased Li-plating on the graphite anode was observed.From the particle to the electrode level, we demonstrate that there remains ample opportunity for optimizing the material properties of conventional electrode chemistries for faster charging and longer-life performance. Our combined use of advanced characterization, modelling, and data-guided manufacturing shows that a multi-scale and multi-modal approach can be applied to build electrodes from the particle up and achieve enhanced electrochemical performance at the cell level through advanced and scalable manufacturing techniques. Figure 1

Failure analysis and reliability assessment of a type of aero-engine combustion chamber thermal barrier coatings

During a routine hole probe inspection, the aviation division found that the combustion chamber flame tube of a V2500 aero engine had failed early and that the TBCs around the vent holes on the flame tube liner panel 4 had peeled off over a large area, causing the flame tube liner to burn through. This work studies the premature failure of the V2500 aero-engine flame tube and, using modeling and simulation tests, finds the reason for premature failure as a substantial area of thermal barrier coating peeling owing to sintering. The sintering procedure significantly increases the thermal barrier coating's Young's modulus, which reduces the coating's resistance to thermal mismatch strain. The reliability of the TBCs was then evaluated using a probabilistic approach. Owing to the non-uniformity of temperature distribution induced by the hot airflow, the lifetime of the TBCs in the high temperature region is only around 3000 h, but the lifetime in the low temperature region is at least 25,000 h. Using the method of hole-probing, the values of the calculated and real outcomes are compared. The relative error is less than 5 %, demonstrating that the suggested approach for evaluating dependability has high credibility and applicability.

Unveiling Challenges and Opportunities in Silicon-Based All-Solid-State Batteries: Thin-Film Bonding with Mismatch Strain.

Li-metal and silicon are potential anode materials in all-solid-state Li-ion batteries (ASSBs) due to high specific capacity. However, both materials form gaps at the interface with solid electrolytes (SEs) during charging/discharging, resulting in increased impedance and uneven current density distribution. In this perspective, the different mechanisms of formation of these gaps are elaborated in detail. For Li-metal anodes, Li-ions are repeatedly stripped and unevenly deposited on the surface, leading to gaps and Li dendrite formation, which is an unavoidable electrochemical behavior. For Si-based anodes, Li-ions inserting/extracting within the Si-based electrode causes volume changes and a local separation from the SE, which is a mechanical behavior and avoidable by mitigating the strain mismatch of thin-film bonding between anode and SE. Si electro-chemical-mechanical behaviors are also described and strategies recommended to synergistically decrease Si-based electrode strain, including Si materials, Si-based composites, and electrodes. Last, it is suggested to choose a composite polymer-inorganic SE with favorable elastic properties and high ionic conductivity and form it directly on the Si-based electrode, beneficial for increasing SE strain to accommodate stack pressure and the stability of the interface. Thus, this perspective sheds light on the development and application of Si-based ASSBs.

New insights into the formation mechanism of the multicomponent carbides (Nb, M)C (M = Ti, Cr and Mn)

Combining first-principles calculations and classical nucleation theory, the results of elemental doping on the structure, electrons and stability of niobium carbides are investigated. Ti, Cr and Mn doping altered the physical characteristics of the carbides, resulting in lower mismatch strains and interfacial energies between the carbide and the substrate. Elemental doping reduced the critical nucleation size of carbides and contributed to the promotion of carbide nucleation. However, excessive doping with Cr and Mn increases the formation energy of carbides and unfavorable to carbide stabilization. Therefore, Cr and Mn are involved in the early elemental aggregation of carbides, while Ti and Nb are the main carbide-forming elements. The nano-precipitated phases of various compositions produced in niobium microalloyed steel were experimentally validated utilizing transmission electron microscopy (TEM) and three-dimensional atom probe tomography (3D-APT). The carbides primarily composed of Nb, Ti and C elements, with the presence of Cr and Mn in the core region leading to the formation of a core-shell structure, which is consistent with theoretical calculations.

The strain-induced transitions of the piezoelectric, pyroelectric, and electrocaloric properties of the CuInP2S6 films

Low-dimensional ferroelectrics, ferrielectrics, and antiferroelectrics are of urgent scientific interest due to their unusual polar, piezoelectric, electrocaloric, and pyroelectric properties. The strain engineering and strain control of the ferroelectric properties of layered two-dimensional van der Waals materials, such as CuInP2(S,Se)6 monolayers, thin films, and nanoflakes, are of fundamental interest and especially promising for their advanced applications in nanoscale nonvolatile memories, energy conversion and storage, nano-coolers, and sensors. Here, we study the polar, piezoelectric, electrocaloric, and pyroelectric properties of thin strained films of a ferrielectric CuInP2S6 covered by semiconducting electrodes and reveal an unusually strong effect of a mismatch strain on these properties. In particular, the sign of the mismatch strain and its magnitude determine the complicated behavior of piezoelectric, electrocaloric, and pyroelectric responses. The strain effect on these properties is opposite, i.e., “anomalous,” in comparison with many other ferroelectric films, for which the out-of-plane remanent polarization, piezoelectric, electrocaloric, and pyroelectric responses increase strongly for tensile strains and decrease or vanish for compressive strains.

Investigation on the helix curvature of bicomponent helical fibers: Numerical simulation and experimental validation

Plant tendril inspired helical structures hold significant promise in various applications. In this study, we advance the understanding of factors influencing the morphology of helical fibers fabricated during co-electrospinning, which is grounded in the mechanism of inducing strain mismatch within the polymer components. Our investigation encompasses a comprehensive analysis of the intrinsic curvature through an updated bilayer strip physical model. Potential factors affecting the resulting curvature of the electrospun helical fibers, including flexibility difference and charge difference within the component pair as well as the evaporation behavior of the chosen solvents for polymers, are explored through numerical simulations and experimental validation.

Integrating State of the Art Zirconia Thermal Barriers with Ytterbium Silicate Environmental Barriers for Silicon-Based Ceramic Turbine Components

AbstractAs gas turbine firing temperatures continue to increase for the sake of improved operating efficiency, the material's transition from Ni-based superalloy components toward ceramic matrix composites (CMCs) is concurrently in progress. Due to the complex nature of the turbine operating environment (envisaged ultrahigh temperatures, presence of water vapor, etc.), coating solutions for these CMCs are still on the forefront of design optimizations. Typically, rare-earth (RE) silicate environmental barrier coatings (EBCs) have been utilized to protect the CMCs from impinging water vapor; however, they lack the thermal insulation properties to enable continued use of simple and/or easily accessible bond coat materials (i.e., silicon). Combined thermal-environmental barrier coatings (T-EBCs) are such a multifaceted surface solution. T-EBCs have been considered in the past, but to this point have not been demonstrated to be technologically robust either due to high implementation costs or complex processing. This study utilizes and combines straightforward and well-established processes—such as plasma-sprayed 7 wt.% yttria-stabilized zirconia—to demonstrate the feasibility of MultiLayered T-EBCs comprised of zirconia-based oxides and RE silicate EBCs in a single coating. The results show that despite high thermal mismatch strains, the structures cannot only be deposited, but also in certain circumstances sustain cyclic thermomechanical loading.

Soft Kirigami Composites for Form‐Finding of Fully Flexible Deployables

AbstractA new class of thin flexible structures is introduced that morph from flat into prescribed 3D shapes through strain mismatch between layers of a composite plate. To achieve control over the target shape, two different concepts are coupled. First, motivated by biological growth, strain mismatch is applied between the flat composite layers to transform it into a 3D shape. Depending on the amount of the applied strain mismatch, the transformation involves buckling into one of the available finite number of deformation modes. Second, inspired by kirigami, portions of the material are removed from one of the layers according to a specific pattern. This dramatically increases the number of possible 3D shapes and allows us to attain specific topologies. An experimental apparatus that allows precise control of the strain mismatch is devised. An inverse problem is posed, where starting from a given target shape, the physical parameters that make these shapes possible are determined. To show how the concept works, it focuses on circular composite plates and designs a kirigami pattern that yields a hemispherical structure. The analysis combines a theoretical approach with numerical simulations and physical experiments to understand and predict the shape transition from 2D to 3D. The tools developed here can be extended to attain arbitrary 3D shapes. The initially flat shape suggests that conventional additive manufacturing techniques can be used to functionalize the soft kirigami composite to fabricate, for example, deployable 3D structures, smart skins, and soft electromagnetic metasurfaces.

Determination of Seasonal Influenza Intrahost Viral Diversity as a Function of Host Immune Status

Abstract Background Seasonal influenza viruses evolve predominately via antigenic drift, the slow accumulations of genetic mutations leading to changes in key antigenic sites. Due to the accumulation of antigenic changes, influenza vaccines must be updated each year and, even then, can suffer from limited efficacy due to strain mismatch. Despite high levels of genetic diversity seen across the population, most studies show that intrahost viral diversity in humans following natural infection is limited. It is unclear where the population-level diversity in influenza virus originates. Previous studies have shown that host characteristics, such as pre-existing immunity, may affect the intrahost viral evolution during a single infection. As very young children have limited immunologic memory, we hypothesize these infections may serve as a source of viral diversity. Methods In this study, we characterize influenza genetic diversity in the pediatric population as a function of age and vaccine status. We use next generation sequencing to assess intrahost influenza virus diversity in 200 clinical isolates generated during the 2017-2018 flu season from children between 6 months and 18 years of age. We quantify intrahost diversity as the number and frequency of mutations of influenza virus present within each clinical isolate. The clinical samples were obtained from left over influenza-positive nasopharyngeal swabs from the Children's Hospital of Philadelphia Infectious Disease Diagnostics Laboratory. We stratify these isolates by host subject age and vaccine status (with respect to that season's influenza vaccine). Results The isolates sequenced thus far fall within the 6B.1A, 6B.1A.1, and 6B.1A.5b clades for H1N1 and 3C.2a.1, 3C.2a2, and 3C.3a1 clades for H3N2, as expected. Thus far, there does not appear to be a significant relationship between the number of variants detected and either the age or vaccine status of the subject for either H3N2 or H1N1, though this may change as additional isolates are sequenced. Conclusions Through ongoing studies, we evaluate how host age and vaccination status influences intrahost viral diversity. Using clinical metadata, we investigate the association between viral diversity and the duration of symptoms and disease severity. By identifying a reservoir of influenza diversity, we will be better able to evaluate influenza strains for inclusion in the seasonal vaccine.

Multiresponsive MXene Actuators with Asymmetric Quantum‐Confined Superfluidic Structures

AbstractMXene, which is known for its high electrical/thermal conductivity, surface hydrophilicity, excellent mechanical flexibility, and chemical stability, is a versatile and smart material for soft actuators. However, most MXene actuators are fabricated by combining MXene with other inert materials to form a bilayer or multilayer structure. Considering the strain mismatch at multimaterial interfaces under frequent deformation, MXene‐based actuators are generally associated with poor stability, which limits their practical applications. Herein, inspired by the natural quantum‐confined superfluidic (QSF) effect, a multiresponsive MXene actuator that can be driven by moisture, light, and electricity by engineering an asymmetric QSF structure on both sides of the MXene film is reported. The actuation mechanism of the MXene film can be attributed to nonuniform water adsorption, transport, and desorption within the asymmetric QSF channels under moisture, photothermal, and electrothermal stimuli. Interestingly, MXene actuators can be flexibly formed into various shapes under moisture‐assisted mechanical compression, which not only enhances their multiresponsive actuation, but also permits a more complex deformation. As proof‐of‐concept demonstrations, various intriguing applications including a dual‐role robot, a smart shielding curtain, and a dragonfly robot, are fabricated, revealing the potential of MXene actuators for soft robotics.

3D Heterogeneous Model for Electrodes in Lithium-Ion Batteries to Study Interfacial Detachment of Active Material Particles and Carbon-Binder Domain

Mechanics plays a crucial role in the performance and lifespan of lithium-ion battery (LIB) cells. Thus, it is important to address the interplay between electrochemistry and mechanics in LIBs, especially when aiming to enhance the energy density of electrodes. Accordingly, this work introduces a framework for a fully coupled electro-chemo-mechanical heterogeneous 3D model that allows resolving the inhomogeneities accompanied by electrochemical and mechanical responses of LIB electrodes during operation. The model is employed to numerically study the mechanical degradation of a nickel manganese cobalt (NMC) cathode electrode, assembled in a half-cell, upon cycling. As opposed to previous works, a virtual morphology for a high-energy electrode with low porosity is developed in this study, which comprises distinct domains of active material (AM) particles, the carbon-binder domain (CBD), and the pore domain to resemble real commercial electrodes. It is observed that the mechanical strain mismatch between irregularly and randomly positioned AM particles and the CBD might lead to local contact detachment. This interfacial gap, in combination with the diminishing contact strength over cell cycling, continuously deteriorates the electrode performance upon cycling by impedance rise and capacity drop. In agreement with previous experimental reports, the presented simulation results exhibit that the contact loss mostly takes place in the regions closer to the separator. Eventually, the resulting gradual capacity drop and change in impedance spectrum over cycling, as the consequence of interfacial gap formation, are discussed and indicated.

Investigation on buried interfacial charge carrier dynamics of the MAPbI3/NiO interface by mismatch strain and termination

Organic-inorganic halide perovskite solar cells (PSCs) have attracted significant attention due to their low cost, simple fabrication process, and rapid improvement in photovoltaic performance. NiO is often considered as a potential hole transport layer (HTL) in these PSCs owing to its wide band gap and deep valence band level. However, uncertainties remain regarding the interfacial charge carrier dynamics at the perovskite/HTL interface induced by the interfacial mismatch strain and terminal configuration. Herein, typical MAPbI3/NiO interfacial terminal configurations (MAI-Ni, MAI-O, PbI-Ni, PbI-O) with strain-configured interfaces were explored by first-principle and device simulation. The results indicate that the binding energy decreases, the carrier transport efficiency increases, and the valence band offset (VBO) decreases as the interfacial atomic configuration of the perovskite surface changes from MAI to PbI. Meanwhile, the compressive strain applied on the perovskite surface also increases the interfacial VBO. The J-V curves and energy band of the PSCs show that the device performance tends to enhance first and then decrease as the positive VBO of the MAPbI3/NiO interface increases. Thus, the strain and termination configuration could modulate the device's photovoltaic performance, which is dependent on the energy band bending caused by the strain and termination configuration. This work provides a valuable understanding of the MAPbI3/NiO interface and contributes new strategies to interface optimization for further improving the photoelectric conversion efficiency of PSCs.

Dynamic Response of Paper-Based Bi-Material Cantilever Actuator

This work presents a dynamic modeling approach for analyzing the behavior of a bi-material cantilever actuator structure, consisting of a strip of filter paper bonded to a strip of tape. The actuator’s response is induced by a mismatch strain generated upon wetting, leading to the bending of the cantilever. The study delves into a comprehensive exploration of the dynamic deflection characteristics of the bilayer structure. It untangles the intricate connections among the saturation, modulus, hygro-expansion strain, and deflection, while uniquely addressing the challenges stemming from fluid–structure coupling. To solve the coupled fluid–solid differential equations, a combined numerical method is employed. This involves the application of the Highly Simplified Marker and Cell (HSMAC) technique for fluid flow analysis and the Finite Difference Method (FDM) for response deflection computation. In terms of the capillary flow model, the Computational Fluid Dynamics (CFD) simulations closely align with the classical Washburn relationship, depicting the wetted front’s evolution over time. Furthermore, the numerical findings demonstrate that heightened saturation levels trigger an increase in hygro-expansion strain, consequently leading to a rapid rise in response deflection until a static equilibrium is achieved. This phenomenon underscores the pivotal interplay among saturation, hygro-expansion strain, and deflection within the system. Additionally, the actuator’s response sensitivity to material characteristics is highlighted. As the mismatch strain evolving from paper hygro-expansion diminishes, a corresponding reduction in the axial strain causes a decrease in response deflection. The dynamic parameter demonstrates that the deflection response of the bilayer actuator diminishes as dynamic pressure decreases, reaching a minimal level beyond which further changes are negligible. This intricate correlation underscores the device’s responsiveness to specific material traits, offering prospects for precise behavior tuning. The dependence of paper modulus on saturation levels is revealed to significantly influence bilayer actuator deflection. With higher saturation content, the modulus decreases, resulting in amplified deflection. Finally, strong concordance is observed among the present fluidically coupled model, the static model, and empirical data—a testament to the accuracy of the numerical formulation and results presented in this study.