A theoretical model for impact protection of flexible polymer material

The relationship between the protective performance of flexible polymer material and material parameters(elasticmodulus,viscosity coefficient)is explored,an impact collision motion equation between two bodies is establishedfrom the viscoelastic material constitutive,and the relationship between the kinematic response and the materialparameters is obtained.Based on the Kelvin constitutive model,a theoretical model for impact between the pro-tective body and the protected body is established,then the dynamic response is obtained.The feasibility of themodel was verified by drop hammer experiment,and the material parameters(elastic modulus,viscosity coeffi-cient)were obtained by formula.The model is discretized and the relationship between local impact response andmaterial parameters is analyzed.The discussion results on the relationship between the impact response and theprotective material performance indicate that adjusting the elastic modulus,viscosity coefficient,and thicknessof the protective material can effectively improve protective effect.

Recent Advances in Design Strategies and Multifunctionality of Flexible Electromagnetic Interference Shielding Materials

With rapid development of 5G communication technologies,electromagnetic interference(EMI)shielding for electronic devices has become an urgent demand in recent years,where the development of corresponding EMI shielding materials against detrimental electromagnetic radiation plays an essential role.Meanwhile,the EMI shielding materials with high flexibility and functional integrity are highly demanded for emerging shielding applications.Hitherto,a variety of flexible EMI shielding materials with lightweight and multifunctionalities have been developed.In this review,we not only introduce the recent development of flexible EMI shielding materials,but also elaborate the EMI shielding mechanisms and the index for"green EMI shielding"performance.In addition,the construction strategies for sophisticated multifunctionalities of flexible shielding materials are summarized.Finally,we propose several possible research directions for flexible EMI shielding materials in near future,which could be inspirational to the fast-growing next-generation flexible electronic devices with reliable and multipurpose protections as offered by EMI shielding materials.

Abrasion test of flexible protective materials on hydraulic structures

In this study, several kinds of flexible protective materials sprayed with polyurea elastomers （hereinafter referred to as polyurea elastomer protective material） were adopted to meet the abrasion resistance requirement of hydraulic structures, and their abrasion resistances against the water flow with suspended load or bed load were studied systematically through tests. Natural basalt stones were adopted as the abrasive for simulation of the abrasion effect of the water flow with bed load, and test results indicate that the basalt stone is suitable for use in the abrasion resistance test of the flexible protective material. The wear process of the polyurea elastomer protective material is stable, and the wear loss is linear with the time of abrasion. If the wear thickness is regarded as the abrasion resistance evaluation factor, the abrasion resistance of the 351 pure polyurea is about twice those of pure polyurea with a high level of hardness and aliphatic polyurea, and over five times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with suspended load. It is also about 50 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load. Overall, the abrasion resistance of pure polyurea presented a decreasing trend with increasing hardness. Pure polyurea with a Shore hardness of D30 has the best abrasion resistance, which is 60 to 70 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load, and has been recommended, among the five kinds of pure polyurea materials with different hardness, in anti-abrasion protection of hydraulic structures.

Recent progress in 2D materials for flexible supercapacitors

High performance supercapacitors coupled with mechanical flexibility are needed to drive flexible and wearable electronics that have anesthetic appeal and multi-functionality. Two dimensional（2D） materials have attracted attention owing to their unique physicochemical and electrochemical properties, in addition to their ability to form hetero-structures with other nanomaterials further improving mechanical and electrochemical properties. After a brief introduction of supercapacitors and 2D materials, recent progress on flexible supercapacitors using 2D materials is reviewed. Here we provide insights into the structure–property relationships of flexible electrodes, in particular free-standing films. We also present our perspectives on the development of flexible supercapacitors.

Mechano-electrochemical perspectives on flexible lithium-ion batteries

With the advent of flexible/wearable electronic devices,flexible lithium-ion batteries(LIBs)have attracted significant attention as optimal power source candidates.Flexible LIBs with good flexibility,mechanical stability,and high energy density are still an enormous challenge.In recent years,many complex and diverse design methods for flexible LIBs have been reported.The design and evaluation of ideal flexible LIBs must take into consideration both mechanical and electrochemical factors.In this review,the recent progress and challenges of flexible LIBs are reviewed from a mechano-electrochemical perspective.The recent progress in flexible LIB design is addressed concerning flexible material and configuration design.The mechanical and electrochemical evaluations of flexible LIBs are also summarized.Furthermore,mechano-electrochemical perspectives for the future direction of flexible LIBs are also discussed.Finally,the relationship between mechanical loading and the electrode process is analyzed from a mechano-electrochemical perspective.The evaluation of flexible LIBs should be based on mechano-electrochemical processes.Reviews and perspectives are of great significance to the design and practicality of flexible LIBs,which is contributed to bridging the gap between laboratory exploration and practical applications.

Finite Element Simulation of Flexible Roll Forming with Supplemented Material Data and the Experimental Verification

Flexible roll forming is a promising manufacturing method for the production of variable cross section products. Considering the large plastic strain in this forming process which is much larger than that of uniform deformation phase of uniaxial tensile test, the widely adopted method of simulating the forming processes with non-supplemented material data from uniaxial tensile test will certainly lead to large error. To reduce this error, the material data is supplemented based on three constitutive models. Then a finite element model of a six passes flexible roll forming process is established based on the supplemented material data and the original material data from the uniaxial tensile test. The flexible roll forming experiment of a B pillar reinforcing plate is carried out to verify the proposed method. Final cross section shapes of the experimental and the simulated results are compared. It is shown that the simulation calculated with supplemented material data based on Swift model agrees well with the experimental results, while the simulation based on original material data could not predict the actual deformation accurately. The results indicate that this material supplement method is reliable and indispensible, and the simulation model can well reflect the real metal forming process. Detailed analysis of the distribution and history of plastic strain at different positions are performed. A new material data supplement method is proposed to tackle the problem which is ignored in other roll forming simulations, and thus the forming process simulation accuracy can be greatly improved.

Ultra-low Young’s modulus and high super-exchange interactions in monolayer CrN: A promising candidate for flexible spintronic applications

Monolayer CrN has been predicted to be half-metallic ferromagnet with high Curie temperature.Due to bulk CrN’s biocompatibility,the monolayer is a promising candidate for bio-related devices.Here,using first-principles calculations based on density functional theory,we find that the formation energy of the bulk CrN stacking from layers with square lattice is only 68 meV/atom above the convex hull,suggesting a great potential to fabricate the monolayer CrN in a square lattice by using molecular beam epitaxy method.The monolayer CrN is then proved to be a soft material with an ultra-low Young’s modulus and can sustain very large strains.Moreover,the analysis of the projected density of states demonstrates that the ferromagnetic half-metallicity originates from the splitting of Cr-d orbitals in the CrN square crystal field,the bonding interaction between Cr-N,and that between Cr-Cr atoms.It is worth noting that the super-exchange interaction is much larger than the direct-exchange interaction and contributes to the ultra-high Curie temperature,which is obtained from Monte Carlo simulations based on Heisenberg model.Our findings suggest that the monolayer CrN can be an indispensable candidate for nanoscale flexible spintronic applications with good biocompatibility and is considerable appealing to be realized in experiment.

Association between Phthalate Exposure and the Use of Plastic Containers in Shanghai Adults

Objective Consuming phthalates may be due to the presence of food contact materials, such as plastic containers. In this study, we investigated the association between plastic container use and phthalate exposure in 2,140 Shanghai adults. Methods Participants completed a questionnaire on the frequency of using plastic containers in different scenarios in the previous year （e.g., daily, weekly） and on the consumption of plastic-packaged foods in the previous three days （yes or no）. Urinary phthalate metabolites were used to assess the association between phthalate exposure and the use of plastic containers. Results The metabolites of di-（2-ethylhexyl） phthalate （DEHP） were the most frequently detected in urine. The results revealed that phthalate exposure was associated with consumption of plastic-packaged breakfast or processed food items in the previous three days. The consumption of these two food items had strong synergistic effects on increasing urinary concentrations of most phthalate metabolites. Conclusion Our results of plastic-packaged breakfast and processed food may be explained by the use of flexible plastic containers, indicating the importance of risk assessment for the application of flexible plastic containers.

Improved design and test of flexible cotton stalks puller

In Xinjiang,in the process of whole stalk harvesting of cotton stalks,there is a problem that the cotton stalks are easily pulled off,and there is an urgent need to develop flexible stalk-pulling machines.Through literature,patent summary,and field research,it is found that domestic researchers have designed many kinds of machines for the problem of easy breaking of cotton stalks,but there is no flexible cotton stalk-pulling machine for the time being.In this study,two flexible cotton stalk-pulling machines were intended to address the problem of easy breakage of cotton stalks.On the basis of the first-generation machine,the design of the second-generation machine was improved.In order to further improve the operational performance of the flexible cotton stalks pulling tools,the operational mechanism of the core working parts of the tools was analyzed and a comparative test was done in a large field.Analysis and the comparative tests proved that improving the clamping working stroke s of the stalk-pulling components can effectively reduce the cotton stalks leakage rate.By using a flexible clamping process,a part of the deformation of cotton stalks can be transferred to the flexible material.To a certain extent,the deformation length L of the contact surface between the cotton stalk and the stalk pulling part is reduced,and the deformation displacementΔy is correspondingly lower.The toughness of the cotton stalk is not significantly decreased and the cotton stalk does not break easily.The improved second-generation machine has a 3.67% to 3.79% lower cotton stalks leakage rate and a 5.65% to 6.30% lower cotton stalks breakage rate than the first-generation machine.As the land in Xinjiang is clay soil,soil bonding to cotton stalks pulling force F2 is larger,resulting in cotton stalks being more difficult to be pulled out of the machine at once.The test proved that the improved second-generation implements had a significant improvement in the cotton stalk-pulling effect because of the subsequent pulling interval CD.The test results verify the analysis results and the research results can provide a theoretical basis for the subsequent structural improvement and performance enhancement of the flexible cotton stalk-pulling machine,which is of reference significance for solving the problem that the cotton stalks are easily pulled and broken in Xinjiang,China.

Flexible,robust and highly efficient broadband nonlinear optical materials based on graphene oxide impregnated polymer sheets

We report a simple solution-processed method for the fabrication of low-cost,flexible optical limiting materials based on graphene oxide(GO) impregnated polyvinyl alcohol(PVA) sheets.Such GO–PVA composite sheets display highly efficient broadband optical limiting activities for femtosecond laser pulses at 400,800,and 1400 nm with very low limiting thresholds.Femtosecond pump–probe measurement results revealed that nonlinear absorption played an important role for the observed optical limiting activities.High flexibility and efficient optical limiting activities of these materials allow these composite sheets to be attached to nonplanar optical sensors in order to protect them from light-induced damage.

Free-standing SnNb_(2)O_(6)@CSN film as flexible anode for high performance sodium-ion batteries

Free-standing electrodes are promising candidates for flexible rechargeable batteries, toward the application of flexible energy storage devices, due to their merits of additive-free, lightweight, and high energy density. Herein, we report a free-standing SnNb_(2)O_(6)@CSN flexible film with SnNb_(2)O_(6) encapsulated in 3D carbon skeleton nanofibers by electrospinning and carbonization processes as flexible anode for sodium-ion batteries(SIBs). The 3D carbon skeleton nanofibers serve as ion/electron transport pathway to improve the electrochemical reaction kinetics and meanwhile alleviate the volume changes of SnNb_(2)O_(6) during charge-discharge processes. The as-constructed half-cell(SnNb_(2)O_(6)@CSN‖Na) exhibits excellent cycling stability of 99.2 m Ah/g at 0.5 A/g after 950 cycles(coulombic efficiency of ~100%) and a high rate performance of 108.6 mAh/g at 10 A/g. In addition, the pouch cell can light up the LEDs at different bending angles(0°, 90°, 180°). This research shows a promising anode material for flexible energy storage electronics.

Virtual climbing: An immersive upslope walking system using passive haptics

Background In virtual environments(VEs),users can explore a large virtual scene through the viewpoint operation of a head-mounted display(HMD)and movement gains combined with redirected walking technology.The existing redirection methods and viewpoint operations are effective in the horizontal direction;however,they cannot help participants experience immersion in the vertical direction.To improve the immersion of upslope walking,this study presents a virtual climbing system based on passive haptics.Methods This virtual climbing system uses the tactile feedback provided by sponges,a commonly used flexible material,to simulate the tactile sense of a user's soles.In addition,the visual stimulus of the HMD,the tactile feedback of the flexible material,and the operation of the user's walking in a VE combined with redirection technology are all adopted to enhance the user's perception in a VE.In the experiments,a physical space with a hard-flat floor and three types of sponges with thicknesses of 3,5,and 8cm were utilized.Results We recruited 40 volunteers to conduct these experiments,and the results showed that a thicker flexible material increases the difficulty for users to roam and walk within a certain range.Conclusion The virtual climbing system can enhance users'perception of upslope walking in a VE.

SnIP-type atomic-scale inorganic double-helix semiconductors: Synthesis, properties, and applications

Flexible inorganic double helical semiconductors similar to DNA have fueled the demand for efficient materials with innovative structures and excellent properties.The recent discovery of tin phosphide iodide(SnIP),the first carbon-free double helical semiconductor at an atomic level,has opened new avenues of research for semiconducting devices such as thermoelectric and sensor devices,solar cells,and photocatalysis.It has drawn significant academic attention due to its high structural flexibility,band gap in the visible spectrum range,and non-toxic elements.Herein,the recent progress in developing SnIP,including its prestigious structure,versatile and intriguing properties,and synthesis,is summarized.Other analogues of SnIP and SnIP-based hybrid materials and their applications in photocatalysis are also discussed.Finally,the review concludes with a critical summary and future aspects of this new inorganic semiconductor.

MXene coupled with molybdenum dioxide nanoparticles as 2D-0D pseudocapacitive electrode for high performance flexible asymmetric micro-supercapacitors

Recently,two-dimensional(2D)transition metal carbides and carbonitrides(MXenes),have shown great potential in micro-supercapacitors(MSCs).However,the maximum voltage output of symmetric MXene MSCs is limited to 0.6 V due to the oxidation effects at high anodic potentials.Herein,we developed asymmetric micro-supercapacitors(AMSCs)based on titanium carbide MXene(Ti_(3)C_(2)Tx)and MXene-MoO_(2) electrodes with an enlarged voltage window of 1.2 V,which is twice wider than that of symmetric MXene MSCs.The 2D-0D MXene-MoO_(2) microelectrode is fabricated by homogenous dispersing zerodimensional(0D)MoO_(2) nanoparticles into MXene layers to impede layers stacking and MoO_(2) nanoparticles aggregation.Notably,the AMSCs delivered good electrochemical performances of areal capacitance of ~19 mF cm^(-2) and volumetric capacitance of 63 F cm^(-3) at a scan rate of 2 mV s^(-1),and high energy density of 9.7 mW h cm^(-3) at a power density of 0.198 W cm^(-3).The AMSCs also presented exceptionally mechanical flexibility under different bending states and excellent cyclic stability,with 88% capacitance retention after 10000 cycles at a discharge current density of 0.5 mA cm^(-2).For practical application,the serially connected AMSCs are fully affordable to power electronics,which is beneficial for soft and wearable power devices.

Flexible supercapacitors based on carbon nanotubes

Since carbon nanotubes（CNTs） possess unique one dimensional（1D） structure, considerable attention has been paid to constructing CNTs into macroscopic materials with different dimensions, including 1D fibers,2D films, and 3D foams. Such macroscopic CNT materials exhibit high conductivity, large surface area, as well as good mechanical properties, and thus can be directly used as the flexible supercapacitor（SC） electrodes or the scaffolds for supporting pseudo-capacitive electrode materials. Based on these macroscopic CNT electrodes, diverse SCs with different structures, including flexible, stretchable and/or compressible fiber and thin film SCs, have been designed. This review provides an overview of recent progress towards the development of flexible SCs based on macroscopic CNTs-based electrodes, with a focus on electrode preparation and configuration design as well as their integration with other multifunctional devices.Future development and prospects in the CNTs-based flexible SCs are also discussed.

Materials and applications of bioresorbable electronics

Bioresorbable electronics is a new type of electronics technology that can potentially lead to biodegradable and dissolvable electronic devices to replace current built-to-last circuits predominantly used in implantable devices and consumer electronics. Such devices dissolve in an aqueous environment in time periods from seconds to months, and generate biological safe products. This paper reviews materials, fabrication techniques, and applications of bioresorbable electronics, and aims to inspire more revolutionary bioresorbable systems that can generate broader social and economic impact. Existing challenges and potential solutions in developing bioresorbable electronics have also been presented to arouse more joint research efforts in this field to build systematic technology framework.

Pencil painting like preparation for flexible thermoelectric material of high-performance p-type Na_(1.4)Co_(2)O_(4) and novel n-type NaxCo_(2)O_(4)

Flexible thermoelectric materials are presented with potential applications in electronic devices and energy conversion due to their convenient preparation,good flexibility,and various forms.However,as ductility is rarely observed in inorganic semiconductors and ceramic insulators,reports on applications of inorganic oxide materials in flexible thermoelectric materials are sparse.Here,we report a new method for the synthesis of a flexible Na_(1.4)Co_(2)O_(4) thermoelectric material based on Na_(1.4)Co_(2)O_(4) bulk materials,which are prepared by a self-flux method and painted on print paper.Seebeck coefficient and power factor of the obtained thermoelectric material are 78-102 μVK^(-1) and 159e223 mWm^-(1)K^(-2),respectively,in a temperature range of 303-522 K,which are superior to those values of other conductive polymers and their compounds.More interestingly,the n-type Na_(1.4)Co_(2)O_(4) flexible material is obtained in the painting process at higher pressure with Seebeck coefficients of109 to183 μVK^(-1) in a temperature range of 303-522 K.The convenient preparation method of these novel flexible thermoelectric materials may be expanded to the synthesis of other flexible thermoelectric materials,which will be the focus of future work.

柔性人工晶状体材料在分子尺度上的纳米压痕和纳米划痕

本文着重研究了折柔性丙烯酸酯人工晶状体在分子尺度下的材料变形和去除机理,为这种柔性材料的超精密抛光奠定了理论基础.通过基于原子力显微镜的纳米压痕实验表明材料在纳米级压痕作用下具有明显的表面效应.随着加载速率的变化,加载曲线在一定程度上偏离了P-h2关系,随着加载速率的增大,材料的粘弹性行为得到较好的抑制.该材料具有明显的尺寸效应,在300–800 nm压痕深度内,材料的纳米硬度由7.7 MPa降至6.4 MPa.纳米划痕实验发现材料摩擦系数急剧下降,然后随着法向载荷的降低而保持稳定,这种现象是由于系统内的摩擦机理由夹杂弹性变形的塑性去除转变为了界面摩擦.此外,通过分子动力学模拟的方法验证了加载速率依赖性现象,诠释了纳米硬度深度依赖性的内在机理.揭示了实验与仿真中载荷-位移曲线和摩擦系数的波动是由于材料分子链的不同运动模式以及材料堆积引起不均匀切深的复合作用.

Material,design,and fabrication of custom prosthetic liners for lower-extremity amputees:A review

As a physical interface,a prosthetic liner is commonly used as a transition material between the residual limb and the stiff socket.Typically made from a compliant material such as silicone,the main function of a prosthetic liner is to protect the residual limb from injuries induced by load-bearing normal and shear stresses.Compared to conventional liners,custom prosthetic lower-extremity(LE)liners have been shown to better relieve stress concentrations in painful and sensitive regions of the residual limb.Although custom LE liners have been shown to offer clinical benefits,no review article on their design and efficacy has yet been written.To address this shortcoming in the literature,this paper provides a comprehensive survey of custom LE liner materials,design,and fabrication methods.First,custom LE liner materials and components are summarized,including a description of commercial liners and their efficacy.Subsequently,digital methods used to design and fabricate custom LE liners are addressed,including residual limb biomechanical modeling,finite element-based design methods,and 3-D printing techniques.Finally,current evaluation methods of custom/commercial LE liners are presented and discussed.We hope that this review article will inspire further research and development into the design and manufacture of custom LE liners.