Flexible Transparent Films Research Articles

Mass-Producible Transparent Flexible Passive-Cooling Film.

Passive cooling is regarded as the desired method for interior temperature regulation due to its advantage of energy consumption reduction. An ideal passive-cooling window is expected to exhibit a high emissivity in the mid-infrared (MIR, 8-13 μm) spectral range for cooling and a low transmittance in the near-infrared (NIR, 780-2100 nm) spectral range for reducing heat flow, while presenting a high transmittance in the visible (VIS, 400-780 nm) spectral range for daylighting. However, material structures that meet these requirements often come with high demands for precision in manufacturing and elevated processing costs, which have limited their potential for large-scale mass production. Here, we propose a mass-producible transparent flexible passive-cooling film that is relatively easy to process and low-cost and meets all of the requirements mentioned above. The film is made of poly(methyl methacrylate) mixed with Cs0.33WO3 nanoparticles, and it shows a high absorptance (80%) in NIR for blocking solar radiation penetration and a high emissivity (93%) in MIR for radiative cooling as well as a reasonable transmittance (40%) in VIS for visibility. Under solar intensity of ∼900 W/m2, a maximum temperature reduction of 8.4 and 7.8 °C has been achieved for a window coated by the film compared to the uncoated window in the condition of the absorbing chamber and car, respectively. Such a mass-producible transparent flexible passive-cooling film holds promising applications in large windows, such as those used in automobiles and buildings, where there is a high demand for both daylighting and cooling.

Flexible transparent ITO thin film with high conductivity and high-temperature resistance

ITO thin films exhibit superior optical characteristics. However, their electrical properties are somewhat less optimal, and they demonstrate limited tolerance under high-temperature conditions. These limitations significantly constrain their potential applications in the domain of optical and electronic devices. In this study, ITO thin films with a thickness of 20 nm were prepared on a flexible Mica substrate. The film has an atomic-level flat surface, high optical transparency (around 85 %), and low resistivity. The stability of the film's surface chemical structure in high-temperature applications was confirmed through XPS characterization. Furthermore, the ITO/Mica flexible thin film demonstrates exceptional durability and recyclability, retaining its optical and electronic properties under a high bending radius of 5 mm and 1000 bending cycles. It is particularly noteworthy that the film's maintenance of good structural and electrical stability (sheet resistance stabilized at 35∼37.5 Ω/sq) under bending cycles at high-temperature (up to 800 °C) conditions, which is crucial for high-temperature resistance in commercial and industrial applications. This study will provide an important experimental basis for the further development and application of ITO thin films in flexible transparent electronic devices with high temperatures and low energy consumption.

Surface engineering of Al2O3 dielectric layer for all-sputtered-oxide transparent and flexible a-IGZO thin film transistor

Transparent flexible display devices have attracted massive attention in recent years owing to their practical applications that can be compatibly adapted to human demand and technological development. Worldwide researchers have studied flexible transparent thin film transistors (TFTs) to qualify them for the backplane component of future transparent and flexible displays. Simplifying the fabrication process of a TFT can be considered a critical need for reducing consumed cost, time, toxic chemicals. In this study, sputtering was utilized as a major fabrication method for manufacturing a transparent oxide TFT device, which demonstrated good mechanical flexibility. A simple surface treatment process was applied to enhance the susceptibility of the sputtered Al2O3 dielectric through multiple coatings of solution processed Al2O3. It is noteworthy that the transparent oxide TFT device exhibits a high optical transparency of 81.12% and good electrical switchability at low operating voltage (3 V) with a decent mobility of 4.37 cm2 V−1 s−1 and proven mechanical durability.

Preparation and optimization of MTO/Ag/MTO transparent flexible film based on co-sputtering at room temperature

Preparation and optimization of MTO/Ag/MTO transparent flexible film based on co-sputtering at room temperature

Transparent and Superhydrophilic Flexible Protein Films with Antifogging and Self-Cleaning Attributes.

Cyanoglycoside-modified flexible protein films, exhibiting a high level of transparency of ≈46 to 83%, were successfully prepared from lysozyme and glycerol with varying amounts of amygdalin (20, 40, and 60%) using water as a solvent. The increasing percentage of amygdalin leads to a drastic improvement of the hydrophilicity of the surface with a decrease in the water contact angle to 5.6°, resulting in superhydrophilicity. The increasing percentage of amygdalin led to a significant improvement in the surface's hydrophilicity, resulting in a reduced water contact angle of 5.6° and achieving superhydrophilicity. This superhydrophilic characteristic is particularly relevant to the excellent antifogging and self-cleaning properties of the resulting protein films. In addition to enhanced flexibility, the films also exhibited considerably improved thermal stability with a 40% loading of amygdalin in the protein solution. The superior mechanical, optical, and thermal properties of amygdalin-modified films are due to the strong hydrogen bonding with the peptides of lysozyme, as evidenced by the disappearance of amide bands in the cured protein films. Therefore, these transparent protein films, with their antifogging and enhanced thermal stability properties, can be potentially used for different packaging and coating applications.

A high‐strength flexible transparent reprocessable polyurea film based on dual dynamic noncovalent interactions

AbstractTo address the issues that waste of resources and environmental pollution caused by discarded materials, dynamic bonds are widely introduced into polymers to endow them with reprocess ability. However, there are some obvious issues in existing research such as poor toughness, low fracture elongation, and inability for repeated reprocessing of materials. Considering above problems, this study introduces dense hydrogen bonding and cation–π interactions into the polyurea system, and develops a high‐performance transparent film based on dual dynamic non‐covalent interactions, which enables the film to be reprocessed. Through the synergy of the dual non‐covalent networks, the film exhibits a high tensile strength of 79.6 ± 3.9 MPa and good hardness (pencil hardness of 4H, elastic modulus of 2.69 GPa). It can effectively resist the scratching of copper brush and maintain more than 97% of its initial mechanical strength after being reprocessed five times. In addition, the film has good adhesion to various substrates, as well as high flexibility (0.5 mm) and excellent optical properties (high light transmission of 91.1% and low haze of 0.94%). This study proposes a novel approach to enable polymer materials to be reprocessed and demonstrates the preparation of a film with great potential in optical protection and wearable devices.

Tetrabutylammonium Tribromide-Induced Synthesis of Silver Nanowires with Ultrahigh Aspect Ratio for a Flexible Transparent Film.

Silver nanowires (AgNWs) have gained significant attention from researchers as a promising material for producing flexible transparent conductive films, which can be utilized in touch and display screens. Thereinto, the ultrahigh aspect ratio AgNW network can theoretically decrease the contact resistance effectively while still retaining considerable mechanical and optical properties. However, fabrication of high-quality AgNWs with a fine diameter and high aspect ratio is still challenging. Herein, a simple and robust approach to synthesize ultrahigh aspect ratio AgNWs is presented. This study successfully fabricated AgNWs with the highest aspect ratio up to ∼4000 and an average length of ∼72 μm by utilizing tetrabutylammonium tribromide as an auxiliary additive. The manifestation of tetrabutylammonium tribromide was proven to be beneficial for the generation of silver seeds and the expansion of AgNWs. The obtained AgNWs were utilized to create a transparent conductive film that showed low sheet resistance of 22.4 Ω/sq and high transmittance and low haze of 87.71 and 4.15%, respectively. The transmittance and haze of the vacant poly(ethylene terephthalate) support were 90.13 and 2.05%, thereby offering great potential for application in flexible transparent electrodes.

Free-standing ultra-thin film with semi-embedded metal nanofiber web for high-performance flexible transparent electrodes

We develop a novel manufacturing process for freestanding conductive nanofiber web films in which metal nanofibers are semi-embedded in polydimethylsiloxane (PDMS) to realize high-performance flexible transparent electrode films. This concept utilizes a sacrificial layer to induce a very thin, free-standing film, and the semi-embedded structure maintains the nanofiber web structure. The excellent adhesion properties of PDMS as well as improved mechanical strength mean that it can be applied to large area devices. In this study, we demonstrate that our approach has improved mechanical strength and excellent conductivity through transparency/conductivity analysis and bending, cycle, and taping tests.

Flexible Transparent Hydrophobic Coating Films with Excellent Scratch Resistance Using Si-Doped Carbonized Polymer Dots as Building Blocks.

Flexible transparent hydrophobic coating films with excellent scratch resistance have important applications in many fields, especially for optical materials. Herein, a hydrophobic composite coating film was prepared and used as a polymer film protective material by combining 3-glycidyloxypropyltrimethoxysilane (GPTMS)-modified Si-doped carbonized polymer dots (Si-CPDs) with mono-trimethoxysilyl-terminated poly(dimethyl siloxane) (PDMS). The Si-CPDs derived from tetramethyl disiloxane propylamine tetraacetic acid and multi-amino oligosiloxanes were successfully prepared via one-step hydrothermal method and then grafted by GPTMS to obtain modified Si-CPDs (mSi-CPDs). Among them, mSi-CPDs act as a matrix layer, and PDMS acts as a low-surface energy layer. Cross-linking the Si-O-Si network of the coating film was formed through sol-gel chemistry. Driven by the hydrophilic-hydrophobic effect, PDMS trends to aggregate at the film surface, thus avoiding the phase separation which can affect transparency. The highly cross-linked network and the presence of hard silica core provide a high hardness to stand the steel-wool scratch. Flexible polymer chains impart the coating film an outstanding bendability. Introduction of PDMS makes the coating film possess hydrophobicity and anti-graffiti function.

Nanostructured Films of Ordered Fe Nanowires for High-Performance Transparent Electromagnetic Interference Shielding

Although metal nanowires (NWs), such as silver NWs, are ideal materials for flexible transparent electromagnetic shielding films, the challenge of obtaining absorptive shielding films with high transmittance and shielding efficiency (SE) still exists. To address this issue, this study used iron nanowires (Fe NWs) with excellent microwave absorbing properties to construct structures with ordered NW distributions. A series of polyethylene terephthalate (PET)/Fe NWs/poly (3,4-ethylenedioxythiophene) (PEDOT) electromagnetic interference (EMI) shielding films were prepared using the magnetic-field-induced orientation. The results demonstrate that the ordered Fe NW network structure can effectively overcome the problem of the trade-off between light transmittance and EMI SE. Specifically, at a Fe NW surface density of 201.78 mg/m2, the ordered PET/Fe NWs/PEDOT films demonstrated a 49.06% increase in light transmittance and a 32.94% increase in EMI SE (19.37 dB), compared to the films with randomly distributed Fe NWs. Furthermore, constructing a double-layer Fe NW network with a stagger angle of 45° at the same surface density increased the EMI SE by 73.2% relative to the monolayer-ordered Fe NW structure, reaching an SE value of 33.54 dB, while maintaining almost unchanged light transmittance. Additionally, the PET/Fe NWs/PEDOT films maintain 97.4% of EMI performance after 3000 bending cycles. Overall, this study provides a new approach for creating high-performance flexible transparent EMI shielding films.

Transparent flexible fluorescent films based on natural rubber composited with quantum dots for traffic equipment

Quantum dots are one of the nanotechnology materials applied in various ways like flexible electronic devices and others. In this work, we study and synthesize semiconductor quantum dots (SQDs) to produce fluorescent natural rubber films by the technique called directed blending. We illustrate the appropriate ratio of mixtures employed in our method such as quantum dot colloidal solutions and natural latex as well as moles between each substance. During the process, the liquid composite and rubber adhesive is applied to the surface for creating flexible fluorescent films that can be dried at room temperature. In addition, these flexible fluorescent films can be covered with diverse curved surfaces applied probably as a traffic device like luminous traffic cones or traffic signs that glow at night. Based on the unique properties of our products, our research provides an application developed from quantum dot nanotechnology.

Cellulose-Based Fluorescent Material for Extreme pH Sensing and Smart Printing Applications.

Environment-responsive fluorescence materials are being widely investigated for instrument-free determination of various environmental factors. However, developing an eco-friendly cellulose-based fluorescent pH sensor for sensing extreme acidity and alkalinity is still challenging. Herein, a highly fluorescent and multifunctional material is developed from biopolymer-based cellulose acetate. A biopolymer-based structure containing responsive functional groups such as -C═O and -NH is constructed by chemically bonding 5-amino-2,3-dihydrophthalazine-1,4-dione (luminol) onto cellulose acetate using 4,4'-diphenylmethane diisocyanate (MDI) as a cross-linking agent. The prepared material (Lum-MDI-CA) is characterized by UV-vis, Fourier transform infrared, 1H NMR, 13C NMR spectroscopies, and fluorescence techniques. The material exhibits excellent aqua blue fluorescence and demonstrates extreme pH sensing applications. Interesting results are further revealed after adding a pH-unresponsive dye such as MTPP as the reference to develop the ratiometric method. The ratiometric system clearly differentiates the extreme acidic pH 1 from pH 2 and extreme alkaline pH 12, 13, and 14 by visual and fluorescence color change response under a narrow pH range. In addition, the material is fabricated into transparent flexible fluorescent films which demonstrate an outstanding UV shielding, security printing, and haze properties for smart food packaging and printing applications.

Gallic Acid-Reduced Graphene Oxide Deposited with Carbon Nanotubes for Transparent Film Heaters

The flexible transparent film heater described in this research was based on graphene, carbon nanotubes (CNTs), and polyethylene terephthalate (PET). Natural polyphenols gallic acid (GA) was chosen as the “green” reducing agent of graphene oxide (GO) to prepare the GA-functionalized GO (GGO). Then, the GGO nanosheets were introduced into the CNT network, and the GGO/CNT-PET composite films were successfully prepared by a simple spraying method. This type of transparent conductive film (TCF) possesses an excellent optoelectronic performance (Rs = 49.1 Ω/sq., T = ca. 80% at 550 nm) and a very low RMS roughness (approximately 6.89 nm). The sheet resistance of the films changed slightly after the 1000 bending cycles and 100 h of air exposure time, which indicated that the film has good mechanical properties and environmental stability. The composite TCFs were further applied to fabricate transparent film heaters (TFHs) and showed excellent Joule heating performance, fast response speed, good cycling stability, long-term stability, and controllable operating temperature (the power density of the TFHs shows an approximate linear behavior), which satisfy the requirements of TFHs in practical applications, such as safe voltage and temperature in wearable devices, the stable controlling temperature in smart windows, fast heating in defoggers, and so on.

Novel active edible food packaging films based entirely on citrus peel wastes

This is the first report on mobilizing three value-added compounds from citrus peel wastes to fabricate novel/cost-effective active edible films with multiple functionalities. Pectin extracted from grapefruit peels (GFP) with improved recovery yields (48.35%), displayed better thermal stability and superior physico-chemical properties to commercial citrus pectin ( CPec ) with regard to methoxylation degree, anhydrouronic acid and moisture contents. Active films plasticized with PEG 400 (25% w/w of polymer) were prepared by solution casting upon incorporating 0.04% (w/v) of grapefruit peel methanolic extract (GFPE) and maltodextrin-encapsulated lemon peel extract (MD-LPE) into grapefruit pectin ( GFPec ; 3% w/v) matrix. The bioactive ingredients and the optimally active ( GFPec -GFPE/MD-LPE) film-forming solutions exhibited strong radical scavenging and antimicrobial activities against foodborne pathogens. SEM micrographs of the optimal active film revealed good dispersion and compatibility of ingredients in agreement with the FTIR data that confirmed no modifications in the film's functional groups. GFPE and MD-LPE capsules synergistically enhanced the tensile strength, thermal, water vapor/UV barrier properties and soil biodegradability of the elaborated transparent flexible films compared to CPec -based films. Wrapping of artificially contaminated cherry tomatoes with optimal active films inhibited the growth of a four-strain cocktail suspension of E. coli O157:H7 by ∼1.6 log units after 6 days of chilled storage. Overall, the study highlights the benefits of citrus wastes valorization, provides evidence of potential applicability of the fabricated novel edible GFPec -based films as candidates for antimicrobial food packaging, shelf life extension of fresh-cut produce, and supports their consideration as promising eco-friendly alternatives to synthetic food packaging materials. • Three value-added compounds were mobilized from citrus peels for film fabrication. • High methoxyl grapefruit pectin showed superiority to commercial citrus pectin. • Free and encapsulated extracts had remarkable antioxidant and cytotoxic activities. • Incorporating both ingredients enhanced thermal and barrier properties of films. • The novel active film inhibited E. coli O157:H7 growth on wrapped cherry tomatoes.

From cotton to functional flexible transparent film for printable and flexible microsupercapacitor with strong bonding interface

A novel functional flexible transparent film with excellent printability, swellability, degradability, and hydroxyl groups is directly developed from natural cotton.

Adaptive and Remote Thermoregulation Enabled with a Highly Stable Transparent Flexible Heating Film

Adaptive and Remote Thermoregulation Enabled with a Highly Stable Transparent Flexible Heating Film

Photodesign and fabrication of surface relief gratings on films of polyimide-based supramolecular systems obtained using host-guest strategy

New supramolecular structures were attained by an original approach based on mixing the concepts of polyamidic acid (PAA) host and an azochromophore guest with hydrogen bonding intermolecular interactions. The materials have been obtained and characterized for use as liquid crystal (LC) alignment layers. The azochromophore was introduced in the PAA solution in different ratio followed by casting on glass plate and thermal treatment to realize a film with imide structure, confirmed by Fourier-transform infrared spectroscopy (FTIR). Thermal analyses indicated that the dye loading in the polymer host slightly reduces the temperature of thermal decomposition from 508 to 466 °C, while glass transition temperature ranges between 244 and 213 °C. UV–Vis data proved that the samples exposure at the wavelengths of 355 nm is beneficial for surface relief gratings (SRGs) formation. Atomic force microscopy (AFM) evidenced the surface structuring of the samples and the changes in the spatial and functional contact area characteristics as a function of azo-dye amount. The attained grating periodicity was about 1 μm, while the depth ranged between 35 and 100 nm depending of the system composition. Surface anisotropy, bearing properties and fluid retention are enhanced upon chromophore incorporation. LCs anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 , which is desirable for LC display applications. • Supramolecular structures, based on a polymer matrix and an azo-dye, are achieved. • Transparent flexible polyimide films with heat resistance up to 466 °C are attained. • As the azo-dye loading increases LASER-made SRGs depth increases from 37 to 81 nm. • Anisotropy, bearing and fluid retention are enhanced upon azo-dye incorporation. • LC anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 .

Large-Scale Preparation of Silver Nanowire-Based Flexible Transparent Film Heaters by Slot-Die Coating.

Highly flexible silver nanowire-based transparent conductive films (AgNWs TCFs) were large-scale fabricated by slot-die coating AgNWs inks on a flexible polyethylene terephthalate (PET) substrate, and further fabricated into a transparent film heater. Appropriate flow rate, coating speed, and AgNWs concentration allow the construction of the 15 cm × 15 cm AgNW TCFs with a sheet resistance (Rs) of less than 20 Ω/sq, a transmittance (T) at 550 nm higher than 95%, and a haze less than 3.5%. The resultant AgNW TCFs heater possesses high uniformity and superior mechanical stability and can reach a Joule heating temperature of 104 °C with a voltage of 12 V. The slot-die coating method has great potential for large-scale production of AgNW based film heaters promisingly used in window defrost and deicer systems.

PDMS micro-dewy spider-web-like metal nanofiber films for fabrication of high-performance transparent flexible electrode with improved mechanical strength

Research to develop next-generation flexible transparent electrode materials using various nanomaterials is being actively pursued, and nanomaterials with sufficient conductivity and transparency for replacing ITO have been realized. However, because numerous nanomaterials are in contact physically and overlap with each other to form a wide conductive two-dimensional space, the mechanical strength of an electrode film composed of nanomaterials and the adhesion to the substrate are limited significantly. In this study, we develop a new fabrication process for microsized polydimethylsiloxane (PDMS) droplet-coated conductive nanofiber web films to achieve high-performance flexible transparent electrode films. This concept is inspired by the structure of a spider web with dew, and PDMS microdroplets with transparency and elasticity mimicking the dew of a spider web are introduced into the film. These PDMS microdroplets can improve the mechanical strength to maintain the nanofiber web structure, as well as improve adhesion with various substrates and films owing to the excellent adhesive properties of PDMS. In this study, we confirm the superiority of our approach via transparency/conductivity analysis as well as bending, cycle, wind resistance, and immersion tests. Because this approach involves an extremely short process time of less than 5 min as well as inexpensive equipment and materials, it is expected to be widely applied to various next-generation optoelectronic devices such as flexible displays and wearable devices.

Use of Nanocellulose to Produce Water-Based Conductive Inks with Ag NPs for Printed Electronics.

The need for more sustainable printed electronics has emerged in the past years. Due to this, the use of nanocellulose (NC) extracted from cellulose has recently been demonstrated to provide interesting materials such as functional inks and transparent flexible films due to its properties. Its high specific surface area together with the high content of reactive hydroxyl groups provide a highly tailorable surface chemistry with applications in ink formulations as a stabilizing, capping, binding and templating agent. Moreover, NC mechanical, physical and thermal properties (high strength, low porosity and high thermal stability, respectively) provide an excellent alternative for the currently used plastic films. In this work, we present a process for the production of water-based conductive inks that uses NC both as a template for silver nanoparticles (Ag NPs) formation and as an ink additive for ink formulation. The new inks present an electrical conductivity up to 2 × 106 S/m, which is in the range of current commercially available conductive inks. Finally, the new Ag NP/NC-based conductive inks have been tested to fabricate NFC antennas by screen-printing onto NC-coated paper, demonstrating to be operative.