Flexible Films Research Articles

Active and passive infrared emittance tuning using optically transparent unpatterned ITO thin films

Tailoring of thermal emittance has applications in smart radiators, camouflage, infrared (IR) scene generation, stealth, and thermal management. Various studies have explored avenues to achieve both passive and active emittance tuning using methods such as meta-surfaces, phase change materials, composites, nanostructure arrays and multi-layer stacks. Most of these methods often involve complex fabrication processes like multilayer depositions and micro/nano patterning, limiting their scalability for large-scale applications. This study presents a straightforward and scalable approach for passive and active emittance tuning using Indium Tin Oxide (ITO) films deposited on a high emissivity flexible polyethylene terephthalate (PET) substrate. By changing the deposition time, the thickness of the ITO film is controlled which changes the observed emissivity of the ITO/PET composite structure over a wide range (0.2–0.94) while maintaining optical transparency. Using this approach for passive emittance tuning, we demonstrate an IR scene generation application. As the ITO film is conducting, by applying voltage to the ITO/PET sheet, its temperature is changed using which active emittance tuning is also achieved. Compared to existing methods of emittance tuning, the presented approach is simpler, gives flexible films with optical transparency, and has the potential for large-scale integration, enabling cost-effective and scalable manufacturing of emittance-tuned surfaces.

Deviceization of high-performance and flexible Ag2Se films for electronic skin and servo rotation angle control

Ag2Se shows significant potential for near-room-temperature thermoelectric applications, but its performance and device design are still evolving. In this work, we design a novel flexible Ag2Se thin-film-based thermoelectric device with optimized electrode materials and structure, achieving a high output power density of over 65 W m−2 and a normalized power density up to 3.68 μW cm−2 K−2 at a temperature difference of 42 K. By fine-tuning vapor selenization time, we strengthen the (013) orientation and carrier mobility of Ag2Se films, reducing excessive Ag interstitials and achieving a power factor of over 29 μW cm−1 K−2 at 393 K. A protective layer boosts flexibility of the thin film, retaining 90% performance after 1000 bends at 60°. Coupled with p-type Sb2Te3 thin films and rational simulations, the device shows rapid human motion response and precise servo motor control, highlighting the potential of high-performance Ag2Se thin films in advanced applications.

Influence of copper-coated graphene films on mechanical and damping properties of bionic laminar CuAlMn matrix composites

Inspired by the structure of nacre, bionic laminar composites composed of 85.6 wt% Cu, 11.9 wt% Al, and 2.5 wt% Mn were prepared using highly flexible Cu-coated graphene films as fillers. The effects of surface modification and graphene films content on the properties were investigated. Results indicated that the loss factor of composites with 0.1 wt% Cu-coated graphene films is improved by approximately 28% and reaches 0.044 compared to uncoated samples. The density and tensile strength are increased by up to 98% and 362 MPa, respectively. This enhancement is attributed to the improved bonding at the graphene films/matrix interface due to the Cu coating, which allows for efficient load transfer. Concurrently, the activation of interlayer sliding in the graphene films dissipates substantial energy. However, an excessive addition of graphene films leads to decreased density and increased internal defects in the composites, resulting in deteriorated properties. This study provides a reference for the preparation of CuAlMn matrix composites with enhanced mechanical and damping properties.

Management of Light Absorption Based on Sidewall Reflection for Fabricating High-Performance Flexible Nano-Coned Sb2Se3 Thin Film Photovoltaics.

High performance and robustness are the key factors to boosting wearable and portable applications. Although the 1D crystal structure makes the Sb2Se3 thin film more tolerant to physical deformation upon bending, the conventional planar structures still cannot undergo repeated mechanical bending due to the induced stress/strain inside devices, which can be well addressed by constructing three-dimensional nanostructures. Besides, the electron diffusion length has two values, 0.3 μm in the [221] direction and 1.7 μm in the [001] direction, in the Sb2Se3 thin film, which limits the absorber thickness, for getting an effective carrier collection; thus, a strong light trapping effect enabling sufficient light harvesting is needed to allow the use of a very thin light absorption layer. Herein, the nanoconed Sb2Se3 solar cells have been designed, and their light absorption behaviors were investigated within a finite-element simulation under the substrate back-reflection, indicating that the reflection of the bottom part always works positively, while the effect of the nanocone sidewall on absorption enhancement largely depends on its geometry, arising from resonant or scattering modes. These results provide a practical guide in designing/establishing an easier/simpler way to fabricate high-performance and mechanically stable flexible nanostructured Sb2Se3 thin film solar cells.

Preparation and characterization of PU/PDA/PPy/Ag flexible composite film for electric heating

Preparation and characterization of PU/PDA/PPy/Ag flexible composite film for electric heating

A High-Gain, High-Efficiency Transparent and Flexible Antenna for Vehicular Communication

A high-gain high-efficiency flexible and transparent film antenna in millimeter-wave is proposed in this paper. Comb structure which can be regarded as developed from the grid array structure is employed to mitigate the loss of the feeding network caused by the lossy metal mesh. The gain of the antenna has low sensitivity to the sheet resistance, which is promising in developing large-scale and high-performance transparent antenna. A large-scale ([Formula: see text]@28[Formula: see text]GHz) antenna is designed and fabricated using transparent metal mesh film with sheet resistance of 0.1[Formula: see text][Formula: see text]/sq and a thin PET film substrate. Bending measurement shows the antenna has excellent mechanical flexibility. A peak gain of 15.92[Formula: see text]dBi, radiation efficiency of 65.1%, optical transparency of 84% and 1,000-times bending are obtained. To the best of our knowledge, it is the highest gain and radiation efficiency flexible-transparent antenna reported thus far, which provides a glass-integrated antenna solution for vehicular communication.

Flexible Porous Ag2Se Films: From Freestanding Inorganic Films to Inorganic‐Network/Organic‐Skeleton Thermoelectric Generators

AbstractSilver selenide (Ag2Se) flexible films are promising near‐room‐temperature thermoelectric candidates for low‐grade heat harvesting. However, existing Ag2Se films are generally attached on substrates, which impedes further flexibility improvement of the films and constrains the scenarios of applications. Here a cost‐effective and scalable strategy is presented, which combines screen printing and annealing, for synthesizing freestanding Ag2Se inorganic films with different densities of pores. High‐density pores and thin thickness endow the films with high flexibility, while films with low‐density pores obtain higher power factor. Furthermore, by utilizing the porous microstructure, a composite structure consisting of a Ag2Se conductive network and an organic polydimethylsiloxane (PDMS) skeleton is fabricated, which further improves films’ stability under bending and torsion. Finally, a flexible thermoelectric generator comprising five Ag2Se/PDMS legs and encapsulated PDMS outputs a voltage of 20.2 mV and a maximum power of 810 nW (the corresponding power density is 5.4 W m−2) at a temperature difference of 30 K, verifying potential application at near room temperature. This work offers a useful paradigm for fabricating substrate‐free Ag2Se porous films with high flexibility for near‐room‐temperature thermoelectric applications.

Multi-band compatible camouflage enabled by phase transition modulation of flexible GST films

With the rapid development of detection technology, there is an urgent need for multi-band compatible camouflage technology, particularly in the visible-infrared band. However, the conflicting requirements between camouflage across different bands and surface thermal management pose significant challenges in achieving synchronized control for multiple bands in diverse application environments and targets. Herein, we propose a spectrally selective emitter leveraging phase-change modulation of Ge2Sb2Te5, capable of achieving effective camouflage in both the visible band and two atmospheric windows over a wide temperature range. The designed emitters exhibit colorful appearances, compatible with various background environments, thereby ensuring the visible camouflage. Meanwhile, the emitters demonstrate low emissivity values of 0.1 in the MWIR band and 0.08 in the LWIR band, effectively reducing the infrared emission through atmospheric windows. The radiative temperatures of the optimized emitters in the MWIR and LWIR bands are reduced by 105°C and 140°C relative to the target surface (200°C), respectively, providing excellent radiative suppression compared to similar studies. Remarkably, the designed emitter still demonstrates robust flexibility, making it suitable for a variety of targets with complex curved surfaces. This work paves the way for designing the flexible visible-infrared compatible camouflage coatings with integrated thermal management functionality.

Recyclable MXene film as SERS sensor with high sensitivity and flexibility adjusted with ZnO quantum dots

Developing flexible substrates with high sensitivity, good reproducibility and recyclability is a major challenge in surface enhanced Raman scattering (SERS) research. Herein, we prepare a recyclable Ti3C2 MXene/ZnO quantum dots (Ti3C2/ZnO) heterostructure film as an efficient SERS sensor with remarkable flexibility using vacuum assisted filtration technique. Benefiting from the more charge transfer (CT) paths, higher CT efficiency provided by oxygen vacancies (OVs) in ZnO QDs and Schottky barrier between Ti3C2 and ZnO QDs, the limit of detection (LOD) for 4-mercaptopyridine (4-MPY) molecules was as low as 1×10−7 M. In addition, the prepared flexible SERS film provided uniform and stable signals for both temporal (storage at room temperature for 60 days) and spatial (RSD = 10.7 %) scales due to the optimal distribution of ZnO QDs in the macroscopic assembly of Ti3C2/ZnO hybrid with excellent reliability and durability. Moreover, the prepared novel flexible SERS sensor achieved self-cleaning by photocatalytically degrading methylene blue (MB) residues extracted from the surface of orange peels and showed exceptional reusability during the detection process. Thus, this high-efficiency and low-cost flexible recyclable SERS sensor may be useful for the in-situ molecular detection in food security and environmental protection.

Stretchable Composite Films Are Prepared by Using Cellulose Pulp with Differential Substitution of Carboxymethyl Cellulose and Thymol with an Infrared Heating Process for Packaging Application.

Herein, cellulose pulp (CP), carboxymethyl cellulose (CMC), and thymol-based eco-friendly, transparent, and flexible composite films are prepared. These materials dissolved well in an environment-friendly process in N-methyl morpholine N-oxide (NMMO) ionic liquids using infrared heating. Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses are used to study the structure, microstructure, and morphology of the composite films. The thermal properties of the CP/CMC/thymol composites are thoroughly studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal stability of the composites (T 5%-57.8-91.2 °C and T 10%-216.6-284.1 °C) significantly improves following the CMC addition. In each case, all the composite film exhibits unique T g (140.5-143.1 °C) values, as confirmed by DSC. The tensile strength of the cellulose pulp is 66.5 MPa, increasing to 78.4 MPa for the CP/CMC-1:0.5 composites and steadily increasing to 93.8 MPa with increasing CMC content. Similarly, CMC increases the EB of cellulose pulp from 9.3 to 7.4%. The water vapor permeability and swelling ratio values of the CP/CMC/thymol composites are in the range of 1.9-2.11 × 10-9 g/(m2·Pa·s) and 52.5-50.8° respectively. The CP, CMC, and thymol-based composite do not exhibit cytotoxicity to the aneuploid immortal keratinocyte cell line and demonstrate excellent antioxidant properties, for promising packaging and biomedical applications.

Flexible Neural Interface From Non-Transient Silk Fibroin With Outstanding Conformality, Biocompatibility, and Bioelectric Conductivity.

Silk fibroin (SF) with good biocompatibility can enable an efficient and safe implementation of neural interfaces. However, it has been difficult to achieve a robust integration of patterned conducting materials (multichannel electrodes) on flexible SF film substrates due to the absence of some enduring interactions. In this study, a thermo-assisted pattern-transfer technique is demonstrated that can facilely transfer a layer of pre-set poly(3,4-ethylenedioxythiophene) (PEDOT) onto the flexible SF substrate through an interpenetrating network of 2 polymer chains, achieving a desired substrate/conductor intertwined interface with good flexibility (≈33MPa), conductivity (386Scm-1) and stability in liquid state over 4 months simultaneously. Importantly, this technique can be combined with ink-jet printing to prepare a multichannel SF-based neural interface for the electrocorticogram (ECoG) recording and inflammation remission in rat models. The SF-based neural interface with satisfied tissue conformability, biocompatibility, and bioelectric conductivity is a promising ECoG acquisition tool, where the demonstrated approach can also be useful to develop other SF-based flexible bioelectronics.

Photofunctional gold nanocluster-based nanocomposite coating for enhancing anti-biofouling and anti-icing properties of flexible films

Elastomeric materials have garnered significant attention across biomedical and industrial fields. Multifunctionality and environmental stability are essential requirements for the application of these materials. Herein, we developed photofunctional gold nanocluster-based nanocomposites (SiO2-AuNC) and coated them on elastomeric polydimethylsiloxane (PDMS) films through one-step way to enhance anti-biofouling and anti-icing properties. The SiO2-AuNC coating, created by immobilizing ultra-small gold nanoclusters (AuNCs) onto hydrophobic silica nanoparticles surface using a gel-sol method, forms an island-like convex structure. The immobilization significantly enhanced radiative transitions and promoted the generation of reactive oxygen species of AuNCs, which provided robust anti-biofouling property through photosensitization to the films. Meanwhile, the rigid SiO2-AuNC nanocomposite markedly enhances the wear resistance of the films. Additionally, the hierarchical micro- and nanostructure of SiO2-AuNC coating increases the hydrophobicity of the films, effectively preventing the aggregation of supercooled water droplets, thereby providing superior and durably anti-icing properties. This one-step coating provides a simple and effective strategy for multifunctional surface modification with nanoparticles, showing potential biomedical and industrial applications.

Self-Stabilized Dispersion Polymerized Aniline/Carbon Nanotubes Based Flexible Interlayer Films for Boosting Performance Characteristics of Lithium-Sulfur Batteries

Self-Stabilized Dispersion Polymerized Aniline/Carbon Nanotubes Based Flexible Interlayer Films for Boosting Performance Characteristics of Lithium-Sulfur Batteries

Study on UV-Curable Acrylic Clear Viscoelastic Materials with Grafted Structures

Flexible substrates are crucial for wearable electronic strain sensors, but achieving biocompatibility, low cost, and aesthetic appeal alongside good mechanical performance remains challenging. Acrylic-based clear viscoelastic films (CVFs) are gaining attention due to their excellent transparency and potential for enhanced mechanical properties. This study synthesized copolymers CVF1-4 with varying branch content using soft monomers 2-ethylhexyl acrylate (2-EHA), butyl acrylate (n-BA), and functional monomer acrylic acid (AA). Employing a "grafting-through" strategy, small molecule monomers, ATRP-synthesized oligomer pBA25, and photoinitiator 1,6-hexanediol diacrylate (HDDA) were in-situ polymerized under UV light to form transparent, flexible elastic films CVF1-4. Between -20 to 80 C, CVF1-4 demonstrated excellent mechanical properties such as low modulus (in the kPa range), low glass transition temperature (below -20 C), large deformation (500-600%), and high strain recovery rate (>95%). Among them, CVF3 with 15% branching showed a balanced comprehensive performance, exhibiting primarily elastic behavior at room temperature. Therefore, selecting appropriate molecular composition and grafting structure provides a simple and customizable solution for optimizing CVF properties.

Natural Rubber Films Reinforced with Cellulose and Chitosan Prepared by Latex Aqueous Microdispersion.

In this paper, green composite films comprising natural rubber (NR), cellulose (CE), and chitosan (CS) were successfully fabricated through a simple, facile, cost-effective method in order to improve mechanical, chemical, and antimicrobial properties of NR composite films. Chitosan with a low molecular weight of 30,000-50,000 g/mol (CS-L) and a medium molecular weight of 300,000-500,000 g/mol (CS-M) was used for the fabrication. The composite films were prepared via a latex aqueous microdispersion method with different weight ratios of NR:CE:CS-L/CS-M. Fourier transform infrared spectroscopy (FTIR) results demonstrated strong interactions of hydrogen bonds between CE and CS-L/CS-M in the composite films. The tensile strength and the modulus of the composite films in dried form were found to significantly increase with the reinforcement of CE and CS-L/CS-M. The maximum tensile strength (13.8 MPa) and Young's modulus (12.7 MPa) were obtained from the composite films reinforced with CE at 10 wt.% and CS-L at 10 wt.%. The high elongation of 500-526% was obtained from the composite films reinforced with CE at 10 wt.% and CS (CS-L or CS-M) at 5.0 wt.%. The modification could also significantly promote antimicrobial activities and chemical resistance against non-polar solvents in the composite films. The NR composite films have potential uses as flexible films for sustainable green packaging.

Exploring the influence of sudan IV Azo dye on the structural, optical, and dispersion characteristics of PVA/Su-IV composites

Flexible polymeric film composites consisting of polyvinyl alcohol (PVA) and Sudan IV azo dye (Su-IV) were synthesized using a casting method. Despite the known optical properties of PVA and azo dyes individually, the combined effects of Su-IV doping in PVA on the material’s optical and nonlinear optical properties have not been thoroughly investigated. This study addresses this gap by exploring the interactions between PVA and Su-IV at various doping concentrations (0.1–0.8 wt%) and their subsequent impact on the material’s structural and optical characteristics. Fourier transform infrared (FTIR) spectroscopy was employed to identify distinct vibrational groups within the composites, revealing that the incorporation of Su-IV induced random deviations in most absorption intensities compared to pristine PVA. Notably, new peaks at 519 and 444 cm−1 emerged, intensifying with increasing Su-IV concentrations, indicating significant interactions between the composite constituents. The optical properties were analyzed through transmittance and reflectance measurements, which uncovered new absorption peaks at 518 and 357 nm in PVA/Su-IV composites. These peaks correspond to electronic energy transitions of 2.4 and 3.6 eV, respectively, and their intensities increased with higher Su-IV content. Additionally, the indirect and direct bandgaps were decreased as Su-IV concentrations increased. The refractive index (n) analysis showed typical dispersion behavior between 850 and 2500 nm, aligning with the Wemple-DiDomenico (WDD) model. Furthermore, the oscillator parameters were calculated. Also, the nonlinear optical susceptibility (χ(3)) was boosted from 4.19 × 10−6 for pure PVA to 3.60 × 10−4 for the sample with 0.8 wt% Su-IV. The nonlinear refractive index (n2) was also measured at 8.55 × 10−2 for the doped sample. These findings demonstrate the potential of PVA/Su-IV composites for applications in nonlinear optics and photonics.

Enhancing the thermoelectric properties of PEDOT:PSS films through the incorporation of g-C3N4 nanosheets and carbon nanotubes

Present study focuses on the synthesis of flexible nanocomposite film made of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), graphitic carbon nitride (g-C3N4) nanosheets, and carbon nanotubes (CNTs) and how the g-C3N4 nanosheets and CNTs affect the thermoelectric properties of PEDOT:PSS. Incorporating 10 wt% of g-C3N4 nanosheets to PEDOT:PSS improved the Seebeck coefficient to 74.3 μVK−1, ∼5 times higher than the PEDOT:PSS film. However, this led to a decrease in electrical conductivity, limiting the power factor to 335.4 μWm−1K−2. In order to address this, CNTs were added as conductive fillers. The resulting PEDOT:PSS composite, with 10 wt% of g-C3N4 and 10 wt% CNTs, showed a significant power factor of 589.8 μWm−1K−2, an electrical conductivity of 810.6 Scm−1, and a Seebeck coefficient of 84.5 μVK−1, indicating a substantial improvement in the thermoelectric performance of pristine PEDOT:PSS. The increased Seebeck coefficient in the PEDOT:PSS and g-C3N4 composite is due to reduced carrier concentration and energy filtering at the interfaces. The enhancement in electrical conductivity and the Seebeck coefficient after adding CNTs is attributed to the formation of conductive networks, increased mobility, and energy filtering at the interfaces between PEDOT:PSS and CNTs. The study suggests that combining g-C3N4 nanosheets and CNTs with PEDOT:PSS could enhance the thermoelectric performance of PEDOT:PSS-based materials.

Tb3+-doped a zero-dimensional all-inorganic metal halide perovskite scintillator Cs2ScCl5·H2O for X-ray imaging

All-inorganic zero-dimensional (0D) metal halide perovskite materials have been widely studied in solid-state lighting due to their unique optical properties. However, there are few researchs on their potential applications in X-ray imaging. Herein, we synthesized an all-inorganic 0D metal halide perovskite scintillator, Cs2ScCl5·H2O:Tb3+, was prepared by using a hydrothermal method. Upon 240 nm excitation, the emission spectrum of Cs2ScCl5·H2O:Tb3+ is primarily composed of characteristic emissions from Tb3+, with the strongest emission peak at 548 nm. Additionally, under X-ray excitation, it exhibits blue light showing an intense emission band centered at 425 nm due to self-trapped (STE) emission, and a rather weaker green emission caused by energy transfer from STE emission to Tb3+ ions. Based on this, a flexible film prepared by using the as-obtained scintillator Cs2ScCl5·H2O:Tb3+ demonstrates real-time X-ray imaging with a resolution of 9.5 lp mm−1. These results suggest the potential application prospect of Cs2ScCl5·H2O:Tb3+ in X-ray detection and imaging.

Surface modification of h‐BN and electric field control of its orientation in sulfonated polyetheretherketone

AbstractSince thermally conductive fillers easily aggregate when introduced into polymer matrix, it is essential to apply a modifier to enhance the dispersion of the filler. In current study, the surface of boron nitride (h‐BN) is firstly modified by employing a double modification process and then added into sulfonated polyetheretherketone (SPEEK) to form the composite materials. Four different kinds of samples of double‐modified h‐BN were obtained. Ultimately, the XXX@h‐BN/SPEEK (XXX denoted as modifier, i.e. PDA, VTMS, TEOS, and APS) flexible film with the horizontally oriented XXX@h‐BN was produced by heating the mixture under an external electric field. The test results indicate that the thermally conductive filler PDA@h‐BN (PDA: polydopamine), which was prepared by modifying OH@h‐BN with PDA, loaded into SPEEK, and electrically oriented, shows the best overall performances. With a high tensile strength of 43.24 MPa and good flexibility, PDA@h‐BN/SPEEK flexible film exhibits an in‐plane thermal conductivity of 2.3 Wm−1 K−1 at a filling ratio of 10 wt%. The sample may be bent at a steep angle without breaking down and can recover to original shape bearing its high degree of flexibility.

Flexible and Recyclable Bio-Based Polyester Composite Films with Outstanding Mechanical and Gas Barrier Properties Using Leaf-Shaped CNT@BNNS Covalent Heterojunction.

With the depletion of petroleum resources, the development of sustainable alternatives for plastic substitutes has grown in importance. It is urgently desirable yet challenging to design high-performance polyesters with extensive mechanical and prominent gas barrier properties. This work uses bio-based PBF polyester as a matrix, "leaf-shaped" carbon nanotube@boron nitride nano-sheet (CNT@BNNS) covalent hetero-junctions as functional fillers, to fabricate CNT@BNNS/PBF (denoted as CBNP) composite films through an "in-situ polymerizing and hot-pressing" strategy. The covalent CNT "stem" suppresses the re-stacking of BNNS "leaf", endowing hetero-structured CNT@BNNS illustrates superior stress transfer and physical barrier effect. The covalently hetero structure and high orientation degree of CNT@BNNS greatly improve the comprehensive performance of the CBNP composites, including excellent mechanical (strength of 76MPa, modulus of 2.3GPa, toughness of 85MJm-3, elongation at break of 193%) and gas barrier (O2 of 0.015 barrer, and H2O of 1.1 × 10-14g cm cm-2s-1Pa-1) properties that are much higher than for pure PBF or other-type polyesters, and most engineering plastics. Moreover, the CBNP composites also boast easy recyclability, overcoming the tradeoff between high performance and easy recycling of traditional plastics, which makes the polyester composite competitive as a plastic substitute.