Flexibility Properties Research Articles

Polyimide aerogel/aramid fiber composite with high mechanical strength and thermal insulation for thermal protective clothing

Polyimide (PI) aerogel, as a new organic aerogel material, has the excellent thermal properties of polyimide and the characteristic of high thermal insulation of aerogels, and has gained increasing attention. In this work, using PI aerogel as the matrix material and aramid fiber as the reinforcement material, controllable flexible PI aerogel/aramid fiber composite insulation materials were successfully prepared by freeze-drying and soft treatment. This study sought to determine how the mass percentage of PI aerogel affected the microstructure, mechanical characteristics, thermal insulation capabilities, and thermal comfort of clothes in PI aerogel/aramid fiber composites. To achieve this, the preparation process of PI aerogel was optimized, and the effects of different mass fractions of PI aerogel on the properties of the composite material were evaluated. The results demonstrated that increasing the mass fraction of PI aerogel led to improvements in the mechanical properties, flexibility, and heat insulation properties of the composite material. Furthermore, the PI aerogel/aramid fiber composite offered enhanced thermal comfort to the wearer in hot and humid environments, indicating that the composite material is particularly suited for thermal insulation applications.

Principle & application of energy storage based on 2D material: Evidence from graphene

The development of new energy and related industries has raised higher requirements for energy storage devices. Graphene, a 2-D carbon material with a single atomic layer thickness, possesses excellent mechanical properties, thermal conductivity, SSA, optical transparency, and rapid electron migration, among other unique physical and chemical properties. The addition of graphene is predicted to enhance the rate performance, durability and energy density of electrochemical energy storage devices. This study summarizes the recent research in the production and application of graphene in electrochemical energy storage devices, primarily focusing on supercapacitors and the positive and negative electrode of lithium-ion batteries. The main roles of graphene include serving as an ultrathin support and buffering material, an active substance, and a conductive material. In addition, the limitations of graphene due to its production technologies and the potential brought by its super flexibility and lightweight properties are discussed. Finally, a brief outlook in the field of graphene is provided.

SENSING MECHANISM AND APPLICATION OF MECHANICAL STRAIN SENSOR: A MINI-REVIEW

This study reviews the potential of flexible strain sensors based on nanomaterials such as carbon nanotubes (CNTs), graphene, and metal nanowires (NWs). These nanomaterials have excellent flexibility, conductivity, and mechanical properties, which enable them to be integrated into clothing or attached to the skin for the real-time monitoring of various activities. However, the main challenge is balancing high stretchability and sensitivity. This paper explains the basic concept of strain sensors that can convert mechanical deformation into electrical signals. Moreover, this paper focuses on simple, flexible, and stretchable resistive and capacitive sensors. It also discusses the important factors in choosing materials and fabrication methods, emphasizing the crucial role of suitable polymers in high-performance strain sensing. This study reviews the fabrication processes, mechanisms, performance, and applications of stretchable strain sensors in detail. It analyzes key aspects, such as sensitivity, stretchability, linearity, response time, and durability. This review provides useful insights into the current status and prospects of stretchable strain sensors in wearable technology and human–machine interfaces.

A smart superwetting PET-Anthocyanin membrane for pH monitoring in water and emulsion separation

Smart superwetting membranes with anti-oil pollutions and process water pH monitoring show great potential before downstream processing. Herein, a flexible intelligent monitoring membrane with strong anti-oil fouling properties was developed by utilizing a PET-Anthocyanin mixed solution through electrospinning. Specifically, using waste PET plastic bottles as raw materials, a dual-solvent system is used to dissolve the PET, and then anthocyanins are added to blend to form an electrospinning solution. The obtained A/PET showed excellent porous morphology and wettability, and its underwater oil contact angle could reach up to 150°. The introduction of anthocyanins (5 %) rich in hydroxyl functional groups reduced the formation of hydrophobic domains and promoted the hydration layer on the membrane surface, showing excellent oil resistance property. Furthermore, the stress–strain test of the A/PET5 membrane shows that the strain is significantly enhanced after the yield phenomenon, which shows that the membrane has a flexible mechanical property. Most importantly, based on the pH-sensitivity of anthocyanins, it can be intuitively found that color response changes from the original pink to light pink, and then to white, showing excellent monitoring the pH of the continuous phase. Moreover, the developed membrane possesses water flux of 7440 L m-2h−1 and oil rejection up to 99.4 % for O/W emulsions, surpassing that of the superhydrophilic PET base membrane (956 L m-2h−1, 99.3 %). Briefly, this work provides a novel multifunctional smart membrane with excellent anti-fouling, flexible mechanical, and outstanding separation performance, which can visually monitor the separation process of oily wastewater.

Physical approach of a neuron model with memristive membranes.

The membrane potential of a neuron is mainly controlled by the gradient distribution of electromagnetic field and concentration diversity between intracellular and extracellular ions. Without considering the thickness and material property, the electric characteristic of cell membrane is described by a capacitive variable and output voltage in an equivalent neural circuit. The flexible property of cell membrane enables controllability of endomembrane and outer membrane, and the capacitive properties and gradient field can be approached by double membranes connected by a memristor in an equivalent neural circuit. In this work, two capacitors connected by a memristor are used to mimic the physical property of two-layer membranes, and an inductive channel is added to the neural circuit. A biophysical neuron is obtained and the energy characteristic, dynamics, self-adaption is discussed, respectively. Coherence resonance and mode selection in adaptive way are detected under noisy excitation. The distribution of average energy function is effective to predict the appearance of coherence resonance. An adaptive law is proposed to control the capacitive parameters, and the controllability of cell membrane under external stimulus can be explained in theoretical way. The neuron with memristive membranes explains the self-adaptive mechanism of parameter changes and mode transition from energy viewpoint.

Progress in the preparation of high-quality wafer-scale monolayer and multilayer MS2 (M = Mo; W) films by CVD

MS2 (M = Mo; W), with natural atomic thickness, are typical two-dimensional (2D) semiconductor materials, which have excellent electronic/optoelectronic properties and mechanical flexible properties. With the development of semiconductor device miniaturization, much attention has been brought to MS2, especially in large-scale integrated circuits, ultra-sensitive photodetectors, and flexible electronic devices. Here, we present the recent research progress on the controllable synthesis of high-quality, wafer-scale, uniform monolayer and multilayer MS2 films by chemical vapor deposition methods, focusing on the most concerning grain orientation control and defect modulation in whole wafer, besides the pursuit of more larger wafer size in MS2 films’ preparation. We also discuss some critical issues in the process of MS2 films growth and give a brief outlook in the controllable preparation of high-quality MS2 films for device application later on.

Robust 2D layered MXene matrix–boron carbide hybrid films for neutron radiation shielding

Large-scale fabrication of neutron-shielding films with flexible or complex shapes is challenging. Uniform and high boron carbide (B4C) filler loads with sufficient workability are needed to achieve good neutron-absorption capacity. Here, we show that a two-dimensional (2D) Ti3C2Tx MXene hybrid film with homogeneously distributed B4C particles exhibits high mechanical flexibility and anomalous neutron-shielding properties. Layered and solution-processable 2D Ti3C2Tx MXene flakes serve as an ideal robust and flexible matrix for high-content B4C fillers (60 wt.%). In addition, the preparation of a scalable neutron shielding MXene/B4C hybrid paint is demonstrated. This composite can be directly integrated with various large-scale surfaces (e.g., stainless steel, glass, and nylon). Because of their low thickness, simple and scalable preparation method, and an absorption capacity of 39.8% for neutrons emitted from a 241Am–9Be source, the 2D Ti3C2Tx MXene hybrid films are promising candidates for use in wearable and lightweight applications.

Flexible phase change materials for low temperature thermal management in lithium-ion batteries

The performance of Li-ion batteries can degrade dramatically at cold ambient temperatures. The excess heat generated during battery operation can be stored by PCMs and then released at low ambient temperatures to insulate the battery. However, PCMs inevitably suffer from easy leakage and poor adaptability. In this study, we prepared a novel Oct/SEBS composite PCM and applied it in a low-temperature Li-ion battery thermal management system. The prepared Oct/SEBS has good shape stability, a sufficiently high latent heat (187.7 J/g), and thermally induced flexibility properties. In addition, the BTMS containing CPCM can exhibit excellent thermal insulation performance, which can insulate the Li-ion battery for more than 30 min even at −20 °C and increase the discharge capacity from 3.78 Ah to 5.49 Ah, which is very beneficial for the operation of the Li-ion battery at low temperatures.

Study on Two-Dimensional Exit Pupil Expansion for Diffractive Waveguide Based on Holographic Volume Grating

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development cycle and complicated processing. In this paper, we first establish a set of two-dimensional (2D) grating ray tracing models, based on which we determine the initial architecture of the dual-region two-dimensional exit pupil expansion (2D-EPE) AR-HMD holographic waveguide diffraction system. Second, we propose a honeycomb coupled grating array and optimize the optical energy utilization and brightness uniformity of the holographic waveguide and use a custom dynamic linked library (DLL) function to implement the ray tracing of the 2D grating and add a probabilistic splitting function to the DLL, which reduces the single simulation time from 11.853 min to 1.77 min. We also propose a holographic lithography device composed of holographic optical elements (HOEs) and a method for preparing HOEs. Finally, in order to obtain the diffraction efficiency preoptimized by the above DLL for the uniformity of the exit pupil brightness and light energy utilization, we inverse design with the preparation process parameters as the optimization variables and develop the adaptable electromagnetic calculation program Holo-RCWA. Using Holo-RCWA with nondominated sorting genetic algorithm II (NSGA-II), we inverse design to obtain the process parameters satisfying the diffraction efficiency distribution, and the optimization time of the whole system is reduced from 2–3 days to 10 h. This work is of great significance for AR/VR applications.

Multifaceted Shape Memory Polymer Technology for Biomedical Application: Combining Self-Softening and Stretchability Properties.

Thiol-ene polymers are a promising class of biomaterials with a wide range of potential applications, including organs-on-a-chip, microfluidics, drug delivery, and wound healing. These polymers offer flexibility, softening, and shape memory properties. However, they often lack the inherent stretchability required for wearable or implantable devices. This study investigated the incorporation of di-acrylate chain extenders to improve the stretchability and conformability of those flexible thiol-ene polymers. Thiol-ene/acrylate polymers were synthesized using 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), Trimethylolpropanetris (3-mercaptopropionate) (TMTMP), and Polyethylene Glycol Diacrylate (PEGDA) with different molecular weights (Mn 250 and Mn 575). Fourier Transform Infrared (FTIR) spectroscopy confirmed the complete reaction among the monomers. Uniaxial tensile testing demonstrated the softening and stretching capability of the polymers. The Young's Modulus dropped from 1.12 GPa to 260 MPa upon adding 5 wt% PEGDA 575, indicating that the polymer softened. The Young's Modulus was further reduced to 15 MPa under physiologic conditions. The fracture strain, a measure of stretchability, increased from 55% to 92% with the addition of 5 wt% PEGDA 575. A thermomechanical analysis further confirmed that PEGDA could be used to tune the polymer's glass transition temperature (Tg). Moreover, our polymer exhibited shape memory properties. Our results suggested that thiol-ene/acrylate polymers are a promising new class of materials for biomedical applications requiring flexibility, stretchability, and shape memory properties.

The role of flexible polymer composite materials properties in energy absorption of three-dimensional auxetic lattice structures

In this work, the ability of lattice structures with 3D periodic auxetic structure to absorb energy have been investigated. The lattice structures were printed using the FDM method from five types of filaments characterized by different strength, plasticity, and viscoelasticity ratios. The mechanical properties of the filaments were determined by tensile, hardness and impact tests. Quasi-static cyclic tests were used to investigate the viscoelastic behavior. The energy absorption ability of lattice structures was determined by compression tests. It has been established that TPU and nylon fibers are inferior to PLA filaments in terms of strength and hardness, but significantly surpass them in terms of the ability to withstand shock loads and damping properties. Significant differences in the mechanisms of strain energy absorption depending on the properties of the initial filaments have been demonstrated. PLA stuctures exhibit high energy values (0.06 – 0.12 J/cm3), but they are brittle and unable to recover their shape. TPU filaments provide the ability to restore shape, but absorb significantly less energy (0.011 J/cm3). Nylon fibers are less durable than PLA, but have a higher absorption energy (0.136 J/cm3) and are more prone to shape recovery. In further optimization of the structure and properties of 3D structures, it is advisable to use combined lattices consisting of materials with different plasticity and damping ability, which is proposed to be combined by mechanical behavior.

Structural engineering of porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCo2O4/CoO for excellent electromagnetic dissipation with flexible and self-cleaning properties

Design of multi-functional microwave absorption materials with strong dissipation ability is a practical approach to address the current issue of electromagnetic radiation pollution. Herein, based on the exchange bias interaction between ferromagnetic and anti-ferromagnetic interfaces, a series of absorbers composed of the porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCo2O4/CoO were successfully prepared via a fairly simple process of one-step calcination. By regulating the calcination temperature, the pore size and porosity of porous carbon, morphology of loaded NPs as well as the electromagnetic response property and impedance matching characteristic in such composites can be modulated. The porous biochar/NiCo2O4/CoO composite prepared under 350 °C possesses a remarkable electromagnetic absorption reflection loss (RL) of –48.41 dB at 9.12 GHz with 2.5 mm thickness, and the effective absorption bandwidth (EAB) of 4.32 GHz with 2.2 mm thickness is located at X band, this is owing to the strong coupling effect of multiple dielectric polarizations, magnetic resonances, and eddy current consumption under matched impedance. In addition, the microwave absorbing patch prepared with this composite exhibits a well-hydrophobic property for self-cleaning function, and the large extensibility with substantial breaking strength endows its practical usage as a flexible absorber.

Recent advancements in liquid metal enabled flexible and wearable biosensors

Wearable biosensors have demonstrated enormous potential in revolutionizing healthcare by providing real-time fitness tracking, enabling remote patient monitoring, and facilitating early detection of health issues. To better sense vital life signals, researchers are increasingly favoring wearable biosensors with flexible properties that can be seamlessly integrated with human tissues, achieved through the utilization of soft materials. Gallium (Ga)-based liquid metals (LMs) possess desirable properties, such as fluidity, high conductivity, and negligible toxicity, which make them inherently soft and well-suited for the fabrication of flexible and wearable biosensors. In this article, we present a comprehensive overview of the recent advancements in the nascent realm of flexible and wearable biosensors employing LMs as key components. This paper provides a detailed exposition of the unique characteristics of Ga-based LM materials, which set them apart from traditional materials. Moreover, the state-of-the-art applications of Ga-based LMs in flexible and wearable biosensors that expounded from six aspects are reviewed, including wearable interconnects, pressure sensors, strain sensors, temperature sensors, and implantable bioelectrodes. Furthermore, perspectives on the key challenges and future developing directions of LM-enabled wearable and flexible biosensors are also discussed.

A novel hybrid deep fuzzy model based on gradient descent algorithm with application to time series forecasting

Deep fuzzy systems are widely used in time series forecasting tasks due to their excellent nonlinear transformation capabilities and interpretability. However, traditional optimization methods and fixed network structures cannot make the deep fuzzy system obtain the expected prediction accuracy and generalization ability. Therefore, a novel hybrid deep fuzzy model (HDFM) is proposed in this paper. Firstly, two types fuzzy modules, namely the type-1 TSK fuzzy module (T1TSKFM) and the interval type-2 TSK fuzzy module (IT2TSKFM), are respectively presented and designed in detail. And, the gradient expressions of the fuzzy parameters, including the antecedent and consequent parameters, are also derived in detail. Secondly, in order to optimize the fuzzy parameters and to further accelerate the module convergence, a novel parameter optimization strategy is presented, combining the gradient descent with the Regularization, the DropRule and the AdaBound algorithms. Thirdly, a new stacked hybrid deep fuzzy architecture is proposed, which can be automatically trained and constructed using the designed T1TSKFM and the IT2TSKFM. Then, the detailed data-driven learning and updating strategy are given in step by step way. In addition, both the layered structure interpretability and the fuzzy rule interpretability are respectively analyzed. This can guarantee that the proposed model not only has the better forecasting accuracy, but also has the higher interpretability. Finally, in order to verify the effectiveness of the proposed method, several comparative experiments are given. Experimental results show that the forecasting performance of the proposed model outperforms the other comparisons, such as the DIRM-DFM, the IT2DIRM-DFM, the DCFS, and the ANFIS method. At the same time, the proposed model has better interpretability and more flexible construction property.

Tailored self-assembly of semi-transparent polymer/clay nanocomposites for gas-barrier applications assisted by aqueous liquid crystalline scaffolds

A new strategy for preparing flexible and semi-transparent gas-barrier coatings was developed using tailored self-assembly of montmorillonite (MMT)/polyvinylpyrrolidone (PVP) nanocomposites assisted by aqueous liquid crystalline (LC) scaffolds. First, we established a composition wherein aqueous MMT exhibited the LC phase in the presence of polyethyleneimine (PEI) and hydrochloric acid (HCl). The viscoelastic rheological features of MMT LC enable the formation of uniform and conformal MMT coatings on various types of substrates, including flat or topographically featured surfaces. Moreover, the MMT LC serves as a structural scaffold that enables the rapid transport of PVP within the inner gallery space of the MMT LC, resulting in the formation of stacked MMT/PVP nanosheets after drying. Owing to its highly aligned layered structure, MMT/PVP exhibited flexible mechanical properties with enhanced hardness and modulus compared to neat MMT. Furthermore, the MMT/PVP can suppress gas permeation, as demonstrated by 0.1 Barrer of H2 permeability for the best coating conditions (containing 63 wt% MMT and 37 wt% PVP), while maintaining semi-transparent optical properties. Considering the aforementioned properties and that all components in MMT/PVP are bio-safe materials, this coating system has potential applications as a gas-barrier coating in conventional packaging materials, food packaging, and H2 storage tanks.

(Re)defining Esotericism

Abstract This article moves past discussing definitions of esotericism to clarifying the nature of definition itself. After reviewing different approaches to definition, we argue that rigid definitions (which propose necessary and sufficient conditions) are problematic, and that fluid definitions (which seek to clarify, explain, teach etc.) are a better alternative. We then discuss homeostatic property cluster definitions, which are like family-resemblance definitions, but with explicit justification for the particular set of defining criteria. We propose a related but more flexible stable property cluster definition of esotericism. It is intended as a useful focus for ongoing discussion, not as a candidate for the single correct definition. Throughout the article, we contrast meaning realism and meaning antirealism (not ontological realism/antirealism), making a case that the latter is more useful in this context. We end by suggesting that our definitional approach has value for exploring both the global spread of western esotericisms and, more importantly, the extent to which esotericism intersects with the semantic fields of comparable categories in other languages and cultures.

Recent advances in La2NiMnO6 double perovskites for various applications; challenges and opportunities

Double perovskites R2NiMnO6 (R = Rare earth element) (RNMO) are a significant class of materials owing to their Multifunctional properties with the structural modifications. In particular, multifunctional double perovskite oxides La2NiMnO6(LNMO) which possess both electric and magnetic orderings, chemical flexibility, versatility, and indispensable properties like high ferromagnetic curie temperature, high absorption rates, dielectrics, etc. have drawn a lot of attention due their rich physics and diverse applications in various technology. This justifies the intense research in this class of materials, and the keen interest they are subject to both the fundamental and practical side. In view of the demands of this material in lead-free perovskite solar cells, photocatalytic degradation of organic dyes, clean hydrogen production, electric tuneable devices, fuel cells, gas sensing, and biomedical applications, there is a need for an overview of all the literature so far, the ongoing research and the future prospective. This review summarised all the physical and structural properties of LNMO such as electric, magnetic, catalytic, and dielectric properties with their underlying mechanisms. This review article provides insight into the scope of studies in LNMO material for exploring unexposed properties in new material research and to identify areas of future investigation of the materials in the double perovskite family.

Polyurethane-Based Nanocomposites for Regenerative Therapies of Cancer Skin Surgery with Low Inflammatory Potential to Healthy Fibroblasts and Keratinocytes In Vitro.

Nanocomposites based on thermoplastic polyurethanes (TPUs) filled with halloysite nanotubes (HNTs) were studied for their physicochemical and biological properties. Nanocomposites containing halloysite nanotube filler contents of 1 and 2% (E+1 and E+2), respectively, were obtained by extrusion. The newly formed E+1 and E+2 nanomaterials exhibited better flexibility and similar thermal properties compared to neat polyurethane. The use of atomic force microscopy (AFM) and differential scanning calorimetry (DSC) thermogram analysis showed that the distribution of halloysite nanotubes in the polymer matrix is more evenly dispersed in the E+1 nanomaterial, where the grains in the E+2 nanomaterial have a greater tendency to form agglomerates. Mechanical tests have shown that nanocomposites with the addition of HNT are characterized by a higher stress at break and elongation at break compared to neat TPU. The results of cytotoxicity tests suggest that the nanocomposite materials express lower toxicity to normal HaCaT and NHDF than to cancer Me45 cells. Further studies showed that the tested materials induced the expression of proinflammatory interleukins IL6 and IL8 in normal cells, but their overexpression in the cancer cell line resulted in cytostatic effects and proliferation reduction. Such a conclusion suggests the possible application of tested materials for regenerative therapies in cancer surgeries.

ZnO/Cellulose nanocomposite: Recent Developments and Future Prospects

Biocomposites are the amalgamation of two or more biodegradable, eco-friendly materials with different chemical and physical properties. Cellulose-based biocomposites are highly in demand because of their good antibacterial activities as well as their high mechanical strength, thermal stability and flexibility properties. In this review paper, ZnO/cellulose biocomposites have been chosen to discuss in detail. ZnO is an n-type, nontoxic, low cost semiconductor with a band gap of 3.4 eV; hence, more preferable over other semiconductor materials for preparing semiconductor-cellulose biocomposites. In recent time, ZnO-cellulose biocomposites have attracted great research attention for optical (UV sensing, shielding, etc.), bioelectronics (antibacterial, drug uses, etc.), mechanical (toughness, etc.), electric (di-electric, etc.), and thermal applications. In the majority of literature, ZnO/cellulose biocomposites are either used in UV-related applications, like in cosmetic products to act as a protector or in antimicrobial activities like food packaging, fungus treatment, etc. In this paper, we have extensively included the literature reported till date on the preparation and characterization of ZnO-cellulose biocomposites. The preferable applications of the as-prepared biocomposites are also discussed in detail to find out the future scope of these biocomposites for practical applications.

Public acceptance of residential photovoltaic installation: A case study in China

Residential photovoltaics (PV) presents an effective means of achieving low-carbon development, owing to its installation flexibility and resource-saving properties. To explore the residents' behavioral intentions to purchase and install residential PV systems, this study collected 1424 samples and analyze the impact of different policies on residents' adoption of residential PV using the theory of TPB and the Partial Least Squares Structural Equation Model (PLS-SEM). The main conclusions are summarized as follows: (1) Bungalow residents exhibit a stronger inclination to install residential PV than building residents. (2) Perceived reward (PR) affects installation intention (II) more than perceived guide (PG) among bungalow residents. (3) Both PR and PG indirectly affect II through Perceived behavioral control (PBC) among bungalow residents. Economic policies, represented by PR, are likely to have more substantial indirect effects than propaganda and guidance policies. The findings suggest that China's recent residential PV installation policies should increase users' trust and guide the future decline of subsidy policy.