Composite Bilayer Research Articles

Next-generation self-adhesive dressings: Highly stretchable, antibacterial, and UV-shielding properties enabled by tannic acid-coated cellulose nanocrystals

Hydrogels with excellent high-water uptake and flexibility have great potential for wound dressing. However, pure hydrogels without fiber skeleton faced poor water retention, weak fatigue resistance, and mechanical strength to hinder the development of the dressing as next-generation functional dressings. We prepared an ultrafast gelation (6 s) Fe3+/TA-CNC hydrogel (CTFG hydrogel) based on a self-catalytic system and bilayer self-assembled composites. The CTFG hydrogel has excellent flexibility (800% of strain), fatigue resistance (support 60% compression cycles), antibacterial, and self-adhesive properties (no residue or allergy after peeling off the skin). CTFG@S bilayer composites were formed after electrospun silk fibroin (SF) membranes were prepared and adhesive with CTFG hydrogels. The CTFG@S bilayer composites had significant UV-shielding (99.95%), tensile strain (210.9 KPa), and sensitive humidity-sensing properties. Moreover, the integrated structure improved the mechanical properties of electrospun SF membranes. This study would provide a promising strategy for rapidly preparing multifunctional hydrogels for wound dressing.

Lowering the Temperature of Solid Oxide Electrochemical Cells Using Triple-Doped Bismuth Oxides.

Despite the great potential of solid oxide electrochemical cells (SOCs) as highly efficient energy conversion devices, the undesirable high operating temperature limits their wider applicability. Herein, a novel approach to developing high-performance low-temperature SOCs (LT-SOCs) is presented through the use of an Er, Y, and Zr triple-doped bismuth oxide (EYZB). This study demonstrates that EYZB exhibits > 147 times higher ionic conductivity of 0.44 S cm-1 at 600 °C compared to commercial Y-stabilized zirconia electrolyte with excellent stability over 1000h. By rationally incorporating EYZB in composite electrodes and bilayer electrolytes, the zirconia-based electrolyte LT-SOC achieves the unprecedentedly high performance of 3.45 and 2.02W cm-2 in the fuel cell mode and 2.08 and 0.95 A cm-2 in the electrolysis cell mode at 700 °C and 600 °C, respectively. Further, a distinctive microstructural feature of EYZB that largely extends triple phase boundary at the interface is revealed through digital twinning. This work provides insights for developing high-performance LT-SOCs.

Influence of Layer-Thickness Proportions and Their Strength and Elastic Properties on Stress Redistribution during Three-Point Bending of TiB/Ti-Based Two-Layer Ceramics Composites

A mathematical model was developed to determine the order of failure of layers in a two-layer ceramics composite and to determine the conditions for achieving the maximum limit load under three-point loading. The model was set in the space of three “bilayer parameters”: the ratio of the thickness of the lower layer to the whole thickness of the beam, the ratio of Young’s moduli of the lower layer to the upper layer, and the ratio of flexural strengths of the materials of the lower layer to the upper layer. The adequacy of the model obtained was confirmed by experimental results on the three-point bending of the experimental specimens. The experimental samples were two-layer composites consisting of a cermet layer TiB/Ti and a layer of α-Ti. The samples were obtained by free self-propagating high-temperature synthesis (SHS) compression and with varying their thickness. The results obtained make it possible to predict in advance which layer, based on the specific bilayer parameters, will trigger the brittle fracture mechanism as well as to set the maximum destructive load of bilayer composites.

Morphological Diagram of Dynamic-Interfacial-Release-Induced Surface Instability.

In this study, a morphological diagram was constructed for quantitatively predicting various modes of surface instabilities caused by the dynamic interfacial release of strain in initially flat bilayer composites comprising an elastomer and a capping layer. Theory, experiment, and simulation were combined to produce the diagram, which enables systematic generation of the following instability patterns: wrinkle, fold, period-double, delamination, and coexisting patterns. The pattern that forms is most strongly affected by three experimental parameters: the elastic modulus of the elastomer, the elastic modulus of the capping layer, and the thickness of the capping layer. The morphological diagram offers understanding of the formation of complex patterns and development of their applications. Critically, the wrinkle alignment can be well controlled by changing the direction of the interfacial release to enable the creation of centimeter-sized and highly ordered lamellar wrinkled patterns with a single orientation on a soft elastomer without the need for costly high-vacuum instruments or complex fabrication processes. The method and diagram have great potential for broad use in many practical applications ranging from flexible electronic devices to smart windows.

A Self-Floating Robust Polyaniline-Wood Composite Fabricated by One-Step In-Situ Polymerization for High-Performance Solar Steam Generation

Abstract Owing to their cost-effectiveness and renewability, wood-based solar steam generators (WSSG) have gained prominence in the field of desalination and water purification. However, conventional bi-layered WSSG is limited by the high energy consumption of fabrication and low strength of the bonding interface, which makes them unsuitable for long-term applications. Here, a unique bi-layered structural composite with polyaniline (PANI) nanorods uniformly incorporated into a 3D mesoporous matrix of natural wood was fabricated via a one-step in-situ polymerization strategy. The PANI decorated wood (PANI-wood) shows ultrahigh sunlight absorptance (∼98.9%) over a broad wavelength range (200–2500 nm) due to the conjugation of coralloid PANI nanorods and wood. Moreover, numerous aligned wood microchannels enable constant and rapid water transport at the air-water interface under the pressure of capillary forces. The highly stable PANI-wood composite shows high potential as an ideal solar steam generator with a high evaporation rate of 1.62 kg m2 h−1, which is significantly higher than those of other previously reported wood-based bi-layered composites. Moreover, PANI-wood exhibits long-term floating and is chemically stable, making it a potential candidate for low-energy photothermal interfacial sewage purification.

Cellulose acetate for a humidity-responsive self-actuator bilayer composite

The use of stimuli-responsive polymers to produce environmentally responsive self-actuators continues to rise. Highly hygroscopic materials are attracting great interest for the design of humidity-responsive self-actuators. In this context, bilayer composites, formed by the coupling of a hygroscopic layer with a non-hygroscopic one, are relevant as they allow for the response to be tuned through the design of the composite layers. Therefore, the meticulous material characterization and the definition of descriptive models of their hygroscopic behavior are the primary steps towards the development of humidity-responsive self-actuators. This study is aimed at measuring and predicting the response of a bilayer composite made of a hygroscopic material layer and a layer of a non-hygroscopic material when subjected to changes in environmental humidity levels, to be used as a humidity-responsive self-actuator. A cellulose acetate was used as the hygroscopic material. Predictions for the induced hygroscopic deformation in the bilayer composite, based on two-physics finite element simulations, are compared to experimental measurements.

Copolymer versus bilayer composite: Electrochemical, electrochromic and capacitive properties of benzotriazole and edot containing conjugated polymers

In this study, benzotriazole-based homopolymer (P-TBtz), copolymer (C-TBtzEdot), and bilayer composites (B-TBtzEdot and B-EdotTBtz) were prepared by electrochemical polymerization. B-TBtzEdot and B-EdotTBtz differ only in the sequential deposition orders onto the ITO electrode. Wise selected materials successfully performed their jobs: TBtz introduced a multichromic property to polymer films and Edot improved the charge storage capacity. Electrochemical characterizations of resulting conjugated polymer films were performed by cyclic voltammetry (CV), chronopotentiometry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). For optical and morphological characterization, UV–vis spectroscopy and scanning electron microscopy (SEM) were used, respectively. According to SEM images, all films have different morphologies. Moreover, upon applied potential, change in the absorption spectra and color change was monitored. Besides, the capacitance value of the polymer films was calculated from cyclic voltammogram and galvanostatic charge-discharge curves. C-TBtzEdot had the highest capacitance value as 97.5 F/g at 2 mV/s and 92 F/g at 0.5 A/g.

Mechanical behavior of bilayer Ti6Al4V composite under quasi-static and dynamic compression

Bilayer structure and homogeneous structure of Ti6Al4V (TC4) alloy were fabricated by High energy ball milling (HEBM) and Fast Hot-Press Sintering (FHPS). The flake TC4 (F-TC4) powders were obtained from spherical TC4 (S-TC4) powders by HEBM, and the bilayer F/S-TC4 composite was prepared from F-TC4 and S-TC4 powders. The microstructure and micro-hardness evolution along the interface of the bilayer composite were investigated. It was found that the hardness decreased gradually from the F-TC4 side to the S-TC4 side. Moreover, an obvious morphology difference in the interface was observed, typical Widmanstatten structure on the S-TC4 side while an equiaxed structure on the F-TC4 side. In addition, the mechanical properties of the alloy and composite with different structures were studied under quasi-static and dynamic compression. The results revealed that the bilayer F/S-TC4 composite showed great strength improvement with little plasticity sacrifice as compared to traditional S-TC4 alloy.

Electromechanical performance of dielectric elastomer composites: Modeling and experimental characterization

Dielectric Elastomer (DE) devices have gained widespread attention in recent years for their ability to generate large, reversible strains in response to electric actuation. However, some DE materials exhibit a viscoelastic nature that detracts from their electromechanical performance in applications requiring precise time-dependent actuation. This study presents an investigation into the feasibility of using multilayered DE composites, comprising commercially available acrylic-based VHB 4905 and natural rubber membranes, to overcome the viscoelastic effects. A comparison of the electromechanical performance of bi-layer and tri-layer DE composites with that of a mono-layer VHB 4910 membrane is carried out through numerical and experimental methods. We present a theoretical model of the DE composite-based bulging actuator, using an energy-based approach and the assumption of homogeneous deformations. The model predicts the time-dependent deflection of the inflated/deflated multilayered DE composites, taking into account the effect of the intervening air column. The predictive capabilities of the model are validated through experiments under both DC and AC operating conditions, and the electromechanical performance of the DE composites is examined for various actuation responses such as resonance, creep, and hysteresis. The bi-layer DE composite is found to be superior in terms of actuation levels, reduced hysteresis, and reduced creep response. The findings of this study hold promise for the development of DE materials with improved actuation capabilities while maintaining dielectric breakdown strength.

Efficient carbon electrode perovskite solar cells with robust buffer interfaces

Carbon electrode perovskite solar cell has great potential in commercial application based on its low cost, superior stability, and facile fabrication process. However, its performance still lags behind that of devices with gold anode, which greatly attributes to the insufficient charge transport and collection at carbon anode side. Herein, efficient anode buffer contact is built by constructing an organic/inorganic composite hole transport bilayer together with strategic carbon precovering/postcovering anode. Adding a charge selective polythiophene (P3HT) layer between perovskite and nickel oxide (NiOx) can reduce charge transfer recombination loss, inhibit moisture infiltration, and crystallographically protect the perovskite underneath from being corroded by carbon paste. Together with a dense and pin-hole free hole transport layer (HTL)/carbon contact through precovering diluted carbon paste, the modified anode buffer interfaces also promote a facilitated charge collection, thus enhancing the photovoltaic performance of low-cost carbon electrode perovskite solar cells to a state-of-the-art value of 20.8% with an enhanced operational stability. This work provides adaptable and robust anode buffer interfaces for efficient, stable and low cost carbon electrode perovskite cells toward commercialization.

Enhanced dielectric energy storage properties in linear/nonlinear composites with hybrid-core satellite C/SiO2@TiO2 nanoparticles

Polymer dielectrics for electrostatic capacitors possess well-recognized advantages, including ultrahigh power density, excellent processability, and unique self-healing capability. Nevertheless, the negative coupling relationship between dielectric permittivity and breakdown strength in dielectrics always constrains the enhancement of energy density, which cannot satisfy the ever-increasing requirements for integrated and miniaturized technologies. Here, a kind of C/SiO2@TiO2 triphase nanoparticle (CST NP) with a hybrid-core satellite structure is prepared and introduced into nonlinear poly(vinylidene fluoride-co-hexafluoropylene) [P(VDF-HFP)] matrix to improve permittivity and polarization. Benefited from the intensified interfacial polarization induced by CST NPs, a high permittivity of ∼18.8, which is approximately 219% that of pure P(VDF-HFP) (∼8.6), is obtained at 10 kHz. Meanwhile, a linear PEI film with high breakdown strength is stacked with the CST/P(VDF-HFP) composites, forming linear/nonlinear CST/P(VDF-HFP)-PEI bilayer composites. Eventually, a high breakdown strength of ∼503.9 kV/mm, a high energy density of ∼4.26 J/cm3, and a high efficiency of ∼91% are simultaneously achieved in the bilayer composite with merely 0.75 wt. % nanoparticles. The linear/nonlinear bilayer structure incorporated with hybrid-core satellite nanofillers offers an effective strategy to design high-performance dielectric energy storage materials.

Bifurcation buckling and the effect of imperfections on the microbuckling of soft materials with periodic microstructure by the finite strain HFGMC micromechanics

Two approaches are presented for the prediction of the microbuckling of composites subjected to compressive loading and undergoing large deformations. In the first one, the finite strain high-fidelity generalized method of cells (HFGMC) micromechanical analysis is successively implemented for the prediction of the ideal bifurcation buckling stress of the composite. In the second approach which considers composites which possesses imperfections (e.g. wavy fibers), a perturbation expansion is adopted. The resulting zero and first-order problems are solved by employing the finite strain HFGMC micromechanics. Here, the ideal critical stress can be readily predicted, and from the form of the waviness growth with applied loading it is possible to estimate the actual bifurcation stress. In addition, in the particular case of a multilayered periodic composites, an exact solution is derived for the prediction of the bifurcation buckling stress. This exact solution is employed to verify the micromechanically predicted critical stresses of bi-layered composites. For fiber-reinforced composites, a comparison with available finite element solution is utilized to verify the micromechanical predictions. Applications of the offered approaches are given for periodically bi-layered composites that consist of five types of hyperelastic materials, and two types for fiber-reinforced composites. The present methods are also implemented to predict the microbuckling stresses of a porous hyperelastic material and lattice blocks whose elements consist of a hyperelastic material.

Dynamic response of metal/polymer bilayer composite with optimized surface porosity by experiment and simulation

Metal/polymer bi-layered composites have been widely applied in vehicles and digital products. However, the metal/polymer joints usually suffer from fracture failure during dynamic load. This work optimizes the surface porosity to obtain good dynamic shear bonding performances of the 5052 aluminum alloy (Al5052)/polymethyl methacrylate (PMMA) interface during the dynamic test. The nominal bonding performance reaches maximum with the Al5052 surface porosity of about 30%/dm2. Simulation with an equivalent macro complementary interfacial model is applied to verify qualitative bonding performance tendencies in the experiment. The experimental data plots are fitted by a piecewise function which includes a power function to represent the fundamental factor and an exponential function to represent the attenuation factor to help propose a method to estimate the porosity range which would achieve better bonding, and to compared with the ideal fitted simulation curves to evaluate the extent of other factors which decrease the dynamic bonding performance. The optimization of the nominal bonding performances obtained by the experiment-led and simulation-supported investigation has given prominence to the significance of the porosity control.

Effect of defects and reinforcements on the mechanical behaviour of a bi-layered panel

This paper investigates the mechanical behaviour of a bi-layered panel containing many particles in one layer and demonstrates the size effect of particles on the deflection. The inclusion-based boundary element method (iBEM) considers a fully bounded bi-material system. The fundamental solution for two-jointed half spaces has been used to acquire elastic fields resulting from source fields over inclusions and boundary-avoiding multi-domain integral along the interface. Eshelby’s equivalent inclusion method is used to simulate the material mismatch with a continuously distributed eigenstrain field over the equivalent inclusion. The eigenstrain is expanded at the centre of the inclusion, which provides tailorable accuracy based on the order of the polynomial of the eigenstrain. As a single-domain approach, the iBEM algorithm is particularly suitable for conducting virtual experiments of bi-layered composites with many defects or reinforcements for both local analysis and homogenization purposes. The maximum deflection of solar panel coupons is studied under uniform vertical loading merged with inhomogeneities of different material properties, dimensions and volume fractions. The size of defects or reinforcements plays a significant role in the deflection of the panel, even with the same volume fraction, as the substrate is relatively thin.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Characterization of Dual-Layer Hybrid Biomatrix for Future Use in Cutaneous Wound Healing.

A skin wound without immediate treatment could delay wound healing and may lead to death after severe infection (sepsis). Any interruption or inappropriate normal wound healing, mainly in these wounds, commonly resulted in prolonged and excessive skin contraction. Contraction is a common mechanism in wound healing phases and contributes 40-80% of the original wound size post-healing. Even though it is essential to accelerate wound healing, it also simultaneously limits movement, mainly in the joint area. In the worst-case scenario, prolonged contraction could lead to disfigurement and loss of tissue function. This study aimed to fabricate and characterise the elastin-fortified gelatin/polyvinyl alcohol (PVA) film layered on top of a collagen sponge as a bilayer hybrid biomatrix. Briefly, the combination of halal-based gelatin (4% (w/v)) and PVA ((4% (w/v)) was used to fabricate composite film, followed by the integration of poultry elastin (0.25 mg/mL) and 0.1% (w/v) genipin crosslinking. Furthermore, further analysis was conducted on the composite bilayer biomatrix's physicochemical and mechanical strength. The bilayer biomatrix demonstrated a slow biodegradation rate (0.374967 ± 0.031 mg/h), adequate water absorption (1078.734 ± 42.33%), reasonable water vapour transmission rate (WVTR) (724.6467 ± 70.69 g/m2 h) and porous (102.5944 ± 28.21%). The bilayer biomatrix also exhibited an excellent crosslinking degree and was mechanically robust. Besides, the elastin releasing study presented an acceptable rate post-integration with hybrid biomatrix. Therefore, the ready-to-use bilayer biomatrix will benefit therapeutic effects as an alternative treatment for future diabetic skin wound management.

Bilayer microneedles based on Bletilla striata polysaccharide containing asiaticoside effectively promote scarless wound healing

The repair of wounds is essential for overcoming injuries, but the process often leads to scars, and the formation mechanism is unclear. Interestingly, Bletilla striata polysaccharide (BSP) is a procoagulant and has anti-inflammatory properties to promote wound healing, which has great research value for scarless wound healing. Herein, we developed a transdermal drug delivery system of BSP/chitosan (CS) composite bilayer dissolvable microneedles (CS-AS-BSP MNs) containing asiaticoside (AS) based on a centrifugation method with a polydimethylsiloxane mould that fulfilled the requirements of wound healing and achieved a scar-free effect. The drug release results showed that this system improved the solubility of AS and maintained the stable release of the drug for a long time. Further experiments indicated that CS-AS-BSP MNs had a good antibacterial effect and reduced the proliferation of human scar fibroblasts. The wound healing effect of CS-AS-BSP MNs was evaluated in an experimental full-thickness-wound rat model, which demonstrated that the covered wound healed completely without scars within 3 weeks. Furthermore, CS-AS-BSP MNs downregulated TGF-β1 and COL Ⅰ, which are fibrosis-related genes, to inhibit scarring. In brief, this study provides a new strategy for meeting the clinical requirements of effective scarless wound dressings.

Chitosan/silk fibroin composite bilayer PCL nanofibrous mats for bone regeneration with enhanced antibacterial properties and improved osteogenic potential

In regenerative medicine and bone tissue engineering, various composite materials are enormously popular, but the final tissue restoration outcome is not always satisfactory. In this study, bilayer-deposited multifunctional nanofiber mats were successfully fabricated with an osteogenic side of silk fibroin/poly (ε-caprolactone) (referred to as SF/PCL) and an antibacterial side of poly (ε-caprolactone)/chitosan (referred to as PCL/CS). The PCL/CS-SF/PCL (referred to as PCSP) mats exhibited biocompatible properties, sufficient hydrophilicity and mechanical properties, as well as a higher breaking strength (3.6 MPa) than the monolayer of SF/PCL mats (1.5 MPa). The antibacterial side of PCSP mats (A-layer) demonstrated ideal antibacterial potency because the survival rate of Escherichia coli (E. coli) (approximately 25 %) and Staphylococcus aureus (S. aureus) (approximately 15 %) were both significantly lower. Subsequently, the plasmid encoding runt related transcription factor 2 (Runx2) was complexed with the osteogenic side of PCSP mats (O-layer) through polyethyleneimine (PEI), thereby enhancing both osteogenesis-related gene expression and the formation of mineralized nodules. Similarly, the implantation of PCSP+Runx2 mats effectively promoted bone tissue generation in vivo. These results indicated the excellent prospects of applying PCSP mats to bone regeneration with gene delivery.

Enhanced Resistive Switching in Flexible Hybrid RRAM Devices With PVK:MoS2/TiO2 Bilayer

High-performance flexible resistive random access memory (RRAM) devices were demonstrated by engineering the switching layer with PVK:MoS2 composite and TiO2 bilayer. These flexible RRAM devices exhibited excellent switching with low SET (1.2 V) and RESET (−1.5 V) voltages, a high repeatability of 1000 cycles, and an excellent retention time of 5000 s with an ON/OFF current ratio more than 102 at a read voltage of 0.2 V, significantly better than neat PVK/TiO2 devices. Moreover, devices with PVK:MoS2/TiO2 bilayer exhibited high stability upon bending with radii up to 7 mm for 100 cycles. Our results indicate that PVK:MoS2/TiO2 composite bilayer can be a promising switching layer candidate for high-performance flexible RRAM devices.

Regulate the interfacial characteristic of emulsions by casein/butyrylated dextrin nanoparticles and chitosan based on ultrasound-assisted homogenization: Fabrication and characterization

In the work, bilayer emulsions stabilized by casein/butyrylated dextrin nanoparticles (CDNP) and chitosan (CS) were prepared based on ultrasound-assisted homogenization. The effects of different homogeneous pressures and various CS concentrations on physical properties and microstructures of bilayer emulsions were investigated. The homogenization condition of 80 MPa was selected to prepare emulsions due to the fact that the emulsion showed the best stability under this condition. Compared with the monolayer emulsion, the bilayer emulsions showed excellent stability (storage, pH, and freeze-thaw cycle) due to the unique interface structure based on composite bilayer interface of CDNP and CS. Meanwhile, the results of optical microscopy, transmission electron microscopy, and confocal laser scanning microscopy showed that emulsion droplets evenly distributed and were cross-linked by CS chains to form a network structure in bilayer emulsions. These results would provide a new insight for the development of bilayer emulsions based on composite interface and bilayer interface. • The layer-by-layer electrostatic deposition was used to prepare bilayer emulsions. • The emulsion droplets were cross-linked by CS chains to form a network. • The bilayer emulsions showed excellent stability. • The bilayer emulsions based on composite interface and bilayer interface.