Ultra-high Flexibility Research Articles

Super-flexible and low-shrinkage polyimide aerogel composites with excellent thermal insulation: Boosted by SiO2 micron aerogel powder

Polyimide (PI) aerogel composites were synthesized using 4,4′-diaminodiphenyl ether (ODA) and 1,3-bis(4-aminophenoxy)neopentane (BAPN) as diamine monomers, and biphenyl-3,3′,4,4′-tetracarboxylic dianhydride (BPDA) as dianhydride monomers. This study examined the impact of varying proportions of SiO2 micron aerogel powder and the addition of BTC on the properties of the composites. The prepared composites showed ultra-high flexibility (180° folded) with the thickness of 3–4 mm, high thermal stability (95 % weight retention at 501 °C) and thermal insulation performance with ultralow thermal conductivity of 0.033 W/(K·m).

Remarkable flexibility in freestanding single-crystalline antiferroelectric PbZrO3 membranes

The ultrahigh flexibility and elasticity achieved in freestanding single-crystalline ferroelectric oxide membranes have attracted much attention recently. However, for antiferroelectric oxides, the flexibility limit and fundamental mechanism in their freestanding membranes are still not explored clearly. Here, we successfully fabricate freestanding single-crystalline PbZrO3 membranes by a water-soluble sacrificial layer technique. They exhibit good antiferroelectricity and have a commensurate/incommensurate modulated microstructure. Moreover, they also have good shape recoverability when bending with a small radius of curvature (about 2.4 μm for the thickness of 120 nm), corresponding to a bending strain of 2.5%. They could tolerate a maximum bending strain as large as 3.5%, far beyond their bulk counterpart. Our atomistic simulations reveal that this remarkable flexibility originates from the antiferroelectric-ferroelectric phase transition with the aid of polarization rotation. This study not only suggests the mechanism of antiferroelectric oxides to achieve high flexibility but also paves the way for potential applications in flexible electronics.

Ultra-flexible self-supporting Ag2Se/nylon composite films for wearable thermoelectric devices

Recently, flexible thermoelectric (TE) generators (f-TEGs) have received a lot of attention. Compared with TE films on flexible substrates, self-supporting composite films prepared by combining TE materials with soft fabrics and thus retaining the inherent advantages of fabrics, such as stretchability, breathability, and flexibility, are more practical and may significantly expand the application of f-TEGs in smart wearable devices. Hence, in this work, a facile and rapid method for preparing ultra-flexible self-supporting Ag2Se/nylon composite films is developed. The composite films with both TE properties and flexibility were obtained by fast selenization of commercial Ag/nylon fiber fabrics in a short time (60 s) at room temperature and then hot pressing at 230 °C in a vacuum. The maximum power factor of an optimized composite film at room temperature can reach 73.7 μW m−1 K−2. Meanwhile, the film exhibits excellent flexibility with the Seebeck coefficient and electrical conductivity decreased by only 7.37 and 8.48% after being bent 4000 repetitions around a round bar with a radius of 4 mm, which exceeds most reported flexible TE films. The ultra-high flexibility is mainly attributed to its high content of the nylon matrix (∼85.05 wt%), the tight bonding between Ag2Se grains, and the good combination between the Ag2Se and nylon matrix. In addition, a 3-leg f-TEG assembled with the optimal film produces a maximum power of ∼1.524 μW (corresponding to a power density of ∼0.47 W m−2) at a temperature gradient of 40.6 K, verifying the good TE performance of the composite film. This f-TEG can also be used as a self-powered temperature sensor, showing potential applications in daily life.

Excellent Energy-Storage Performance in Lead-Free Capacitors with Highly Dynamic Polarization Heterogeneous Nanoregions.

Lead-free dielectric ceramics with excellent energy-storage performance are crucial to the development of the next-generation advanced pulse power capacitors. However, low energy-storage density limits the evolution of capacitors toward lightweight, miniaturization, and integration. Here, an effective strategy of constructing highly dynamic polarization heterogeneous nanoregions is proposed in lead-free relaxors to realize an ultrahigh energy-storage density of ≈8.0 J cm-3 , making almost ten times the growth of energy-storage density compared with pure Bi0.5 Na0.5 TiO3 ceramic, accompanied by a higher energy efficiency of ≈80% as well as an ultrafast discharge rate of ≈20ns. Ultrasmall polarization heterogeneous nanoregions with different orientations and ultrahigh flexibility, and significantly decreased grain size to submicron lead to reduced heat loss, improved breakdown electric field and polarization, enhanced relaxation, and delayed polarization saturation behaviors, contributing to the remarkable energy-storage performance. Moreover, the breakdown path distribution or electrical tree evolution behaviors are systematically studied to reveal the origin of ultrahigh breakdown electric field through phase field simulations. This work demonstrates that constructing highly dynamic polarization heterogeneous nanoregions is a powerful approach to develop new lead-free dielectric materials with high energy-storage performance.

Chemically bonded multi-nanolayer inorganic aerogel with a record-low thermal conductivity in a vacuum.

Inorganic aerogels have exhibited many superior characteristics with extensive applications, but are still plagued by a nearly century-old tradeoff between their mechanical and thermal properties. When reducing thermal conductivity by ultralow density, inorganic aerogels generally suffer from large fragility due to their brittle nature or weak joint crosslinking, while enhancing the mechanical robustness by material design and structural engineering, they easily sacrifice thermal insulation and stability. Here, we report a chemically bonded multi-nanolayer design and synthesis of a graphene/amorphous boron nitride aerogel to address this typical tradeoff to further enhance mechanical and thermal properties. Attributed to the chemically bonded interface and coupled toughening effect, our aerogels display a low density of 0.8mg cm-3 with ultrahigh flexibility (elastic compressive strain up to 99% and bending strain up to 90%), and exceptional thermostability (strength degradation <3% after sharp thermal shocks), as well as the lowest thermal conductivities in a vacuum (only 1.57mW m-1 K-1 at room temperature and 10.39mW m-1 K-1 at 500°C) among solid materials to date. This unique combination of mechanical and thermal properties offers an attractive material system for thermal superinsulation at extreme conditions.

High Thermoelectric Performance and Ultrahigh Flexibility Ag2S1–xSex film on a Nylon Membrane

Flexible thermoelectric (TE) generators have recently attracted increasing attention as they have the potential to power wearable devices using the temperature difference between the human body and the environment. Ag2S is recently reported to have plasticity near room temperature; however, it has very low electrical conductivity, leading to its poor TE property. Here, to improve the TE property, different amounts of Se (Se/Ag2S molar ratios being 0.4, 0.5, and 0.6) solid solution-substituted Ag2S films on a nylon membrane are prepared by combing wet-chemical synthesis, vacuum filtration, and hot-pressing. The film (Se/Ag2S molar ratio = 0.6) exhibits a better TE performance with a power factor of 477.4 ± 15.20 μW m-1 K-2 at room temperature, which is comparable to that of bulk Ag2S1-xSex. In addition, the film possesses excellent flexibility (only ∼5.4% decrease in electrical conductivity after 2000 times bending along a rod with a radius of 4 mm). The power density of a 6-leg TE generator assembled with the film is 6.6 W/m2 under a temperature difference of 28.8 K. This work provides a facile new route to Ag2S-based TE films with low cost, high TE performance, and ultrahigh flexibility.

Large-Scale Silver Sulfide Nanomesh Membranes with Ultrahigh Flexibility.

The growth of flexible semiconductor thin films and membranes is highly desirable for the fabrication of next-generation wearable devices. In this work, we have developed a one-step, surface tension-driven method for facile and scalable growth of silver sulfide (Ag2S) membranes with a nanomesh structure. The nanomesh membrane can in principle reach infinite size but only limited by the reactor size, while the thickness is self-limited to ca. 50 nm. In particular, the membrane can be continuously regenerated at the water surface after being transferred for mechanical and electronic tests. The free-standing membrane demonstrates exceptional flexibility and strength, resulting from the nanomesh structure and the intrinsic plasticity of the Ag2S ligaments, as revealed by robust manipulation, nanoindentation tests and a pseudo-in situ tensile test under scanning electron microscope. Bendable electronic resistance-switching devices are fabricated based on the nanomesh membrane.

Novel Highly Flexible PCB Design Based on a Via-Less Meander Ground Structure to Transmit mm-Wave RF Signals in 5G Foldable Mobile Products

Recently, new form factors, such as foldable, have increased demand for mobile products.Moreover, mobile phones should support the RF signal frequency up to the mm-wave frequencydue to the expansion of 5G mobile products. Therefore, 5G foldable products require componentsthat facilitate both mm-wave RF transmission and ultra-high flexibility for interconnecting throughthe hinge structure of foldable products. To improve flexibility, a flexible PCB must be thin with noground vias in its bending section; in contrast, the low-loss flexible PCB for mm-wave transmissionmust be thick and have many ground vias, so there is a trade-off relationship between flexibilityand RF characteristics. This paper proposes a new flexible PCB structure that does not experienceproblems regarding signal transmission to the mm-wave band, even when folded 200,000 times.To overcome the physical limits of the trade-off relationship, an interlayer air-gap was formed; astructure with a via-less and meander ground shape is proposed. The simulated loss of the proposedstructure was 0.0254 dB/mm @ 10 GHz, and the isolation between signals ranged from 21.98 dBto 10 GHz. The simulated results of insertion loss and isolation were experimentally verified. Theproposed structure is currently being applied to the RF flexible PCB that interconnects through thehinge of a foldable phone, and is currently being mass-produced.

Versatile Inorganic Subnanometer Nanowire Adhesive.

Adhesives are applied extensively in daily life and industries, and people have developed numerous commercial polymeric adhesives. However, in most cases, these adhesives work on dry surfaces in air and form permanent bonds with the substrates, limiting the applications of adhesives. Inspired by the innate adhesive functions of some animals, such as geckos, spiders, mussels, and clingfish, scientists have developed various adhesive compositions and structures to meet various conditions. Here, we show a versatile subnanometer nanowire (SNW) adhesive with high strength and great reversibility, which could be prepared at a large scale through a facile room-temperature reaction. The SNW adhesive contacts the substrates at multiple sites due to the ultrahigh flexibility, and meanwhile, the multilevel interactions among the SNWs endow them with strong cohesion, so they exhibit good adhesive performance. This adhesive is applicable to various substrates, such as metals, polymers, and glass, and not only possesses good stability at room temperature in air but also is suitable for underwater environments and ultralow temperatures. Moreover, this adhesive could be easily recycled and removed from the substrates without any residue and damage. The SNW adhesive not only inspires the design of hierarchical adhesive structures with new contact modes but also has potential for practical applications.

Porous Flexible Wood Scaffolds Designed for High-Performance Electrochemical Energy Storage

Natural wood has been physically or chemically modified to create new hierarchical structures for vast applications. We report herein the facile methods to synthesize porous flexible conductive wood for high-performance energy storage. Our delignification and densification increase micro–mesopores for higher surface area but decrease macropores to improve the scaffold’s density, thus leading to ultra-high flexibility and excellent mechanical strength. Such hydroxyl-enriched flexible wood scaffolds (FW-RC) are readily chemically deposited with carbon nanotubes (CNTs) to promote fast electron/ion transport and a lower internal resistance (ca. 2.1 Ω). Interestingly, the as-prepared CNT@FW-RC electrode exhibited organic redox reactions originating from oxygen-containing groups on the wood surface. The electrode showed an areal specific capacitance of 640 mF cm–2 at a 0.1 mA cm–2 scan rate and over 93% capacitance retention for 10,000 galvanostatic charge/discharge cycles, outperforming most reported carbonized wood electrodes. Asymmetric supercapacitors demonstrated a maximum energy density of 108 mW h L–1 at the power density of 2.06 W L–1, which retains a value of 36 mW h L–1 at the highest volumetric power density of 20.5 W L–1. Further in situ electrodeposition of conducting polymers on the CNTs@wood electrodes was explored for scalable energy storage devices. The design strategies surely provide guidance on constructing porous flexible wood-based hierarchical nanostructures for emerging applications, utilizing surface functional groups of the wood surface for organic redox reactions.

Shape-stable and smart polyrotaxane-based phase change materials with enhanced flexibility and fire-safety

With the high performance of intelligent electronic machines and the popularity of flexible and foldable devices and high-speed/large capacity 5G communication, the market demand for flexible heat storage and smart temperature control materials are gradually rising. Therefore, phase change materials (PCMs) have received much attention in the related energy storage and temperature control field. As the amount of PCM increases, so do the fire safety concerns associated with their applications. Therefore, the development of improved the flexibility and fire safety for advanced PCMs is imperative. In this work, we reported a pentaerythritol phosphate modified sustainable polyrotaxane as PCMs for thermal energy storage and thermal management. The structure of pentaerythritol phosphate was adequately confirmed by 13C NMR, 31P NMR and ATR-FTIR. Subsequently, the tensile properties, fire safety, phase change performances and shape memory properties of the PCMs were fully analyzed. The results showed that all the flexibility, fire safety and thermal conductivity of modified polyrotaxanes were enhanced remarkably compared to those of pristine polyrotaxane. Further with the high form stability, and excellent cycle stability, the modified polyrotaxanes are therefore promising sustainable and fire safe shape-stable PCMs for thermal energy storage. Notably, its ultra-high flexibility (with elongation higher than 1000%), processing ability, excellent form-stability, enhanced fire-safety (with UL94 V-0 rating and LOI of 33.0%) and thermal conductivity (0.47 W m−1 K−1) provide a practical way for the safe and intelligent heat treatment for some electronic devices, such as solid-state disk.

Quantitative Investigation of the Morphologically Corrugated CVD-Grown Graphene Monolayer Surface with a Nanoparticle-on-Mirror System

Graphene can be used as a starting material for the synthesis of useful nano-complexes for flexible, transparent electrodes, therapeutic, bio-diagnostics, and bio-sensing. In order to apply graphene in the medical field, the chemical vapor deposition (CVD) method has been mainly utilized considering its large and near-homogeneous carbon constituents. Especially, the less degree of perturbation of graphene monolayer (GM), which is followed by the underneath catalytic Cu surface morphology, is very crucial in terms of providing the suspended GM and relatively fluent lateral carrier mobility with lower sheet resistance value. In this work, we can suggest a surface-enhanced Raman spectroscopic (SERS) indicator in a quantitative way on the status of z-directional morphological corrugation of a CVD-grown GM (CVD-GM) by applying a nanoparticle-on-mirror (NPoM) system composed of Au nanoparticle (NP)/CVD-GM/Au thin film (TF) plasmonic junction structure. A new (or enhanced) radial breathing-like mode (RBLM) SERS signal around ~ 150 cm−1 from CVD-GM spaced in NPoM is clearly observed by employing a local z-polarized incident field formed at the Au NP–Au TF plasmonic gap junctions. With this observation, the value of I[out-of-plane, RBLM]/I[in-plane, [2D] at certain domains, can be suggested as a new optical nano-metrology value to relatively determine between lower z-directional morphological corrugation (or protrusion) status of a CVD-GM spaced in our NPoM system (lower I[RBLM]/I[2D] value) and a higher degree of lateral carrier mobility of the CVD-GM associated with lower sheet resistance values as a result of higher blue-shifted Raman in-plane (G, 2D) peak maximum position. Furthermore, we will also expect the bio-sensing performances by utilizing the high specific surface area and ultrahigh flexibility of the CVD-GM in one of the future prospective works such as pressure-strain, strain-to-electricity, and chemical-coupled sensor via I[RBLM]/I[2D] values.Graphical abstract

High-Quality Zno/Ag/Zno Multilayer with Ultra-High Flexibility and Excellent Photoelectric Performance Prepared by Sputtering

High-Quality Zno/Ag/Zno Multilayer with Ultra-High Flexibility and Excellent Photoelectric Performance Prepared by Sputtering

High-Quality Zno/Ag/Zno Multilayer with Ultra-High Flexibility and Excellent Photoelectric Performance Prepared by Sputtering

High-Quality Zno/Ag/Zno Multilayer with Ultra-High Flexibility and Excellent Photoelectric Performance Prepared by Sputtering

Development of piezoresistive PDMS/MWCNT foam nanocomposite sensor with ultrahigh flexibility and compressibility

Polymer foam nanocomposites attract great interest in many wide ranges of biomedical and healthcare monitoring applications. In this study, we investigated the effect of porosity and multi-walled carbon nanotube (MWCNT) content on the piezoresistivity, sensitivity, and mechanical properties of Polydimethylsiloxane (PDMS)/MWCNT foam nanocomposite. The foam nanocomposites were fabricated by particulate leaching method and their electrical and mechanical characteristics were investigated using the different porosity levels (60% and 70%) and different conductive nanofiller contents (0.5 wt.% and 1 wt.%). The foam nanocomposites with 0.5 wt.% MWCNT content and 60% porosity possessed higher pressure sensitivity, higher gage factor, and lower electrical hysteresis along with higher mechanical properties. Moreover, fabricated PDMS/MWCNT foam nanocomposite demonstrated high flexibility, high compressibility, and high recoverability in addition to limited mechanical hysteresis (less than 3%) with a large dynamic sensing range. Contrary to the existing foam nanocomposite samples in the literature, PDMS/MWCNT foam nanocomposites withstood higher pressure ranges (3.5–5 MPa) at limited thickness (average 2.3 mm) without experiencing noticeable macroscopic damage.

Ultra-high flexibility amidoximated ethylene acrylic acid copolymer film synthesized by the mixed melting method for uranium adsorption from simulated seawater

If U(VI) in seawater (unconventional uranium resource) can be extracted efficiently, it can provide important supplies and guarantees for the stable development of nuclear power. In this study, a mixing melting method without condensation agent was proposed to prepare ultra-high flexibility and different proportions DAMN modified EAA resin film (EAA-DAMN) through the condensation reaction between -COOH and -NH2 and the uniform mixing of liquid EAA and DAMN. In addition, the dense film structure and -CN of EAA-DAMN were transformed into multiple pores structure and amidoxime groups of the amidoximated EAA (AO-EAA) by amidoxime reaction. The AO-EAA-3 showed the most excellent adsorption performance (qe=146.40 mg g−1) at pH = 5, which was 2.33 times that of EAA. Moreover, a hypothesis was proposed for the first time that -NH2 in the material could combine with H+ ionized by water to form -NH3+, and then adsorbed NO3- in the solution through electrostatic attraction, and O element from NO3- adsorbed on the surface and N-O from amidoxime groups of material as the adsorption active sites performed coordination with U(VI), thereby improving the adsorption performance of AO-EAA.

Advanced 3D-printed phase change materials

Advanced 3D-printed phase change materials

Strain‐sensing behavior of flexible polypropylene/poly(ethylene‐co‐octene)/multiwalled carbon nanotube nanocomposites under cyclic tensile deformation

AbstractIn this study, the associations between the structural evolution and physical properties of polypropylene/poly(ethylene‐co‐octene)/multiwalled carbon nanotube (PP/POE/MWCNTs) composites were established. The MWCNTs particles preferentially migrating from PP matrix to disperse in POE phase, which contributed to a richer network structure, thus resulting in a significant improvement for electrical conductivity, as well thermal stability, and toughness property with the elongation at break from 300% to 800%. Furthermore, the online strain‐resistance analysis showed that introducing POE phase had a big advantage in improving the recovering resilience and stability of the conductive network structure of PP/POE/MWCNTs composites under a multi‐time circular tensile test with a strain of 5%. It was highlighted that the maximum and minimum electrical conductivity levels of PP/POE composites remained almost constant and even the ratio of the real‐time resistance to the initial one was negative just at the beginning of each circulation regarding the strain stretching and recovery. This was attributed to the oriented conductive network structure of PP/POE nanocomposites induced by the applied strain, thereby increasing the electrical conductivity. Overall, this research provides a basic guidance for preparing composites with ultrahigh flexibility and stability under a circular deformation, which is an essential element taken into consideration for smart sensors with high sensitivity.

Highly-flexible monolithic integrated infrared electrochromic device based on polyaniline conducting polymer

The widespread use of the flexible infrared electrochromic device (IR-ED) fundamentally depends on not only the IR emissivity modulation ability of the functional layer but the component assembling structures. However, building integrated assembling structure for excellent flexibility and service life is an urgent but a challenging task due to exfoliation of the components of the traditional sandwich structure IR-ED during the use of bending and folding. Herein, we employed both sides of gold-plated nylon porous membrane as ion transport layer and electrode layer to construct highly-flexible monolithic integrated IR-ED. The dodecyl benzene sulfonate acid (DBSA)-doped PANI films were electrodeposited on the both side of gold-plated nylon porous membrane. Then the electrolyte was filled into the nylon porous membrane to successfully construct the highly-flexible monolithic integrated IR-ED. Compared with the traditional sandwich structure IR-ED, the unique configuration endows excellent IR electrochromic performance, ultra-high flexibility and structural stability. The monolithic integrated IR-ED can reversibly convert between colored state (dark green) and bleached state (golden yellow) upon the imposed external voltages, and the IR emission modulation of 0.43 and 0.40 is obtained at the wavelength ranges of 8–14 µm and 2.5–25 µm. The illustrated capabilities make the highly-flexible monolithic integrated IR EC device promising for thermoregulation related technologies and adaptive camouflage platforms.

Polyrotaxane: New generation of sustainable, ultra-flexible, form-stable and smart phase change materials

The development of thermal energy storage materials is the most attractive strategy to harvest the solar energy and increase the energy utilization efficiency. Phase change materials (PCMs) have received much attention in this research field for several decades. Herein, we reported a new kind of PCM micro topological structure, design direction, and the ultra-flexible, form-stable and smart PCMs, polyrotaxane. The structure of polyrotaxane was fully confirmed by 1H nuclear magnetic resonance, attenuated total reflection-fourier transform infrared and X-ray diffraction. Then the tensile properties, thermal stability in the air, phase change energy storage and shape memory properties of the films were systematically analyzed. The results showed that all the mechanical performance, thermal stability in air and shape memory properties of polyrotaxanes were enhanced significantly compared to those of polyethylene oxide (PEO). The form stability at temperatures above the melting point of PEO significantly increased with the α-CD addition. Further with the high phase transition enthalpy and excellent cycle performance, the polyrotaxane films are therefore promising sustainable and advanced form-stable phase change materials for thermal energy storage. Notably, its ultra-high flexibility, remolding ability and excellent shape memory properties provide a convenient way for the intelligent heat treatment packaging of complex and flexible electronic devices. In addition, this is a totally novel insight for polyrotaxane application and new design method for form-stable PCMs.