Transparent Polymer Films Research Articles

Highly transparent, writable and photoluminescent foldable polymer film: When fluorescent dyes or pigments join cellulose-based microgel

We prepared a self-dispersed cellulose-based microgel via chemically bonding hydrophilic gelatin peptide chain onto cellulose glucose chain. Following, a variety of highly transparent, foldable, and writable photoluminescent polymer films was obtained through loading organic dyes and inorganic pigments onto cellulose-based microgel matrix, respectively. Benefiting from the coupling sites and network effect of microgel as well as the abundant hydroxyl, amino, and imino groups in its structure, the microgel containing organic dyes and inorganic pigments exhibit good dispersion and stability, and the resultant photoluminescent films emit bright yellow, orange, yellow-green, and blue-green fluorescence under UV light, respectively, especially the cellulose-based microgel stabilized inorganic alkaline earth aluminate hybrids exhibit continuous luminescence for a long time in the dark. Compared with the existing regenerated cellulose or CNCs-based fluorescent films, the cellulose-based microgel fluorescent films present higher transmittance and good biodegradability. This study can bring new ideas for the development of flexible luminescent devices.

Au/SiO2-Nanolaminated Plasmonic Nanoantennas as Refractive-Index-Insensitive and Transparent Surface-Enhanced Raman Spectroscopy Substrates

Surface-enhanced Raman spectroscopy (SERS) has become a powerful technique for ultrasensitive biochemical detection providing molecular fingerprint information. Due to the strong dependence of surface plasmon resonance wavelength on plasmonic nanostructures’ surrounding refractive index (RI), SERS enhancement factors (EFs) at hotspots are sensitive to changes in background RI, which is detrimental to quantitative SERS biochemical analysis in real-world applications with spatially and temporally varying RI matrices. This work reports on a tapered-shape nanolaminate plasmonic nanoantenna (TNLNA) platform that supports multiple, spatially overlapped, hybridized magnetoelectric localized surface plasmon modes revealing high SERS EFs (>107) and an insensitivity to background RI variations (between 1.30 and 1.60). Furthermore, we demonstrate that the uniform arrays of TNLNAs can be manufactured on flexible transparent polymer films to achieve backside-excitable and reversible SERS measurements for in situ label-free glucose monitoring on a skin phantom.

Ice‐Templated, Large‐Area Silver Nanowire Pattern for Flexible Transparent Electrode

AbstractFlexible transparent electrodes are critically important for the emerging flexible and stretchable electronic and optoelectronic devices. To this end, transparent polymer films coated with silver nanowires (AgNWs) have been intensively studied in the past decade. However, it remains a grand challenge to achieve both high conductivity and transmittance in large‐area films, mainly due to the poor alignment of AgNWs and their high junction resistance. Here, the successful attempt to realize large‐area AgNW patterns on various substrates by a 2D ice‐templating approach is reported. With a relatively low dosage of AgNWs (4 µg·cm−2), the resulted flexible electrode simultaneously achieves high optical transmittance (≈91%) and low sheet resistance (20 Ω·sq−1). In addition, the electrode exhibits excellent durability during cyclic bending (≈10 000 times) and stretching (50% strain). The potential applications of the flexible transparent electrode in both touch screen and electronic skin sensor, which can monitor the sliding pressure and direction in real‐time, are demonstrated. More importantly, it is believed that the study represents a facile and low‐cost approach to assemble various nanomaterials into large‐area functional patterns for advanced flexible devices.

Using Transparent Conducting Coatings for Warming Transparent Roofs

The possibility of using multilayer structures based on transparent polymeric films with conducting coatings as heaters for removing snow cover is discussed. It is established that the heaters with cellular polycarbonate slabs 4 mm in thickness are more efficient. The specific capacity spent by these heaters on warming by 20°C is 300 W/m2; for comparison, the capacity of the heaters pasted to the insulating glass unit surface is 420 W/m2.

Layered composite for a geopolygon mire

We have investigated flexible composite materials of test objects (mires) intended for setting the aviation optical equipment for remote sensing of the Earth. The brightness fields and control images of the mire contrasting elements are obtained by the method of ink-jet printing on banner fabric. We have proposed a new layered structure of the material for the operating contrast control. We have established quantitative patterns of changes in the optical characteristics of test objects when using an outer layer made of a transparent polymer film, which makes it possible to vary the characteristics of test objects for adjusting thermal imaging devices and aviation optical equipment using low-cost polygraphic methods.

Embedding Silver Nanowires into a Hydroxypropyl Methyl Cellulose Film for Flexible Electrochromic Devices with High Electromechanical Stability.

Transparent conductive films (TCFs) based on silver nanowires (AgNWs) are becoming one of the best candidates in realizing flexible optoelectronic devices. The AgNW-based TCF is usually prepared by coating AgNWs on a transparent polymer film; however, the coated AgNWs easily detach from the polymer underneath because of the weak adhesion between them. Herein, a network of AgNWs is embedded in the transparent hydroxypropyl methyl cellulose film, which has a strong adhesion with the AgNWs. The obtained TCF shows high optical transmittance (>85%), low roughness (rms = 4.8 ± 0.5 nm), and low haze (<0.2%). More importantly, owing to the embedding structure and strong adhesion, this TCF also shows excellent electromechanical stability, which is superior to the reported ones. Employing this TCF in a flexible electrochromic device, the obtained device exhibits excellent cyclic electromechanical stability and high coloring efficiency. Our work demonstrates a promising TCF with superior electromechanical stability for future applications in flexible optoelectronics.

Super Gas Barrier of a Polyelectrolyte/Clay Coacervate Thin Film.

Transparent polymeric thin films with high oxygen barrier are important for extending the shelf life of food and protecting flexible organic electronic devices. Polyelectrolyte/clay multilayer nanocoatings are shown to exhibit super gas barrier performance, but the layer-by-layer assembly process requires numerous deposition steps. In an effort to more quickly fabricate this type of barrier, a polyelectrolyte/clay coacervate composed of branched polyethyleneimine (PEI), poly(acrylic acid) (PAA), and kaolinite (KAO) clay is prepared and deposited in a single step, followed by humidity and thermal post-treatments. When deposited onto a 179 µm poly(ethylene terephthalate) (PET) film, a 4 µm coacervate coating reduces the oxygen transmission rate (OTR) by more than three orders of magnitude, while maintaining high transparency. This single-step deposition process uses only low-cost, water-based components and ambient conditions, which can be used to for sensitive food and electronics packaging.

The Influence of UV on the Production of Free Terpenes in Vitis vinifera cv. Shiraz

Terpenes contribute to the desirable flavour and aroma of grapes and wine. The biosynthesis of these plant secondary metabolites is influenced by both physiological and environmental factors, such as grapevine phenological stage and sunlight exposure. In this study, we investigated the influence of ultraviolet (UV) at different grapevine phenological stages on free terpenes in grape at harvest. Two types of transparent polymer films were applied to grape bunches to eliminate both UV-A and UV-B or only eliminate UV-B, followed by the identification and quantification of terpenes using headspace solid-phase microextraction with gas chromatography–mass spectrometry (HS–SPME–GC–MS) analysis. In all, 27 free terpenes were identified, including eight monoterpenes/monoterpenoids, four norisoprenoids and fifteen sesquiterpenes. Higher concentrations of γ-terpinene, linalool and β-damascenone were observed in grapes with UV-B attenuation compared to the naturally exposed grape bunches. Elevated α-muurolene was observed in UV-attenuated grapes from pre-veraison to harvest, while higher concentrations of γ-cadinene were observed in naturally exposed grapes. The impacts of UV exclusion on grape terpenes at harvest were specific to phenological stages, where applying UV films from veraison to intermediate ripeness reduced the concentrations of key terpenes in grape harvest and UV attenuation from intermediate ripeness to harvest promoted the accumulation of α-muurolene and γ-cadinene. This study provides information for viticulturists to better manage grape terpene composition through UV shading.

UV-Blocking, Transparent, and Antioxidant Polycyanoacrylate Films.

Applications of cyanoacrylate monomers are generally limited to adhesives/glues (instant or superglues) and forensic sciences. They tend to polymerize rapidly into rigid structures when exposed to trace amounts of moisture. Transforming cyanoacrylate monomers into transparent polymeric films or coatings can open up several new applications, as they are biocompatible, biodegradable and have surgical uses. Like other acrylics, cyanoacrylate polymers are glassy and rigid. To circumvent this, we prepared transparent cyanoacrylate films by solvent casting from a readily biodegrade solvent, cyclopentanone. To improve the ductility of the films, poly(propylene carbonate) (PPC) biopolymer was used as an additive (maximum 5 wt.%) while maintaining transparency. Additionally, ductile films were functionalized with caffeic acid (maximum 2 wt.%), with no loss of transparency while establishing highly effective double functionality, i.e., antioxidant effect and effective UV-absorbing capability. Less than 25 mg antioxidant caffeic acid release per gram film was achieved within a 24-h period, conforming to food safety regulations. Within 2 h, films achieved 100% radical inhibition levels. Films displayed zero UVC (100–280 nm) and UVB (280–315 nm), and ~15% UVA (315–400 nm) radiation transmittance comparable to advanced sunscreen materials containing ZnO nanoparticles or quantum dots. Transparent films also exhibited promising water vapor and oxygen barrier properties, outperforming low-density polyethylene (LPDE) films. Several potential applications can be envisioned such as films for fatty food preservation, biofilms for sun screening, and biomedical films for free-radical inhibition.

Mirroring Solar Radiation Emitting Heat Toward the Universe: Design, Production, and Preliminary Testing of a Metamaterial Based Daytime Passive Radiative Cooler

A radiative cooling device, based on a metamaterial able to mirror solar radiation and emit heat toward the universe by the transparency window of the atmosphere (8–13 µm), reaching and maintaining temperatures below ambient air, without any electricity input (passive), could have a significant impact on energy consumption of buildings and positive effects on the global warming prevention. A similar device is expected to properly work if exposed to the nocturnal sky, but during the daytime, its efficacy could be affected by its own heating under direct sunlight. In scientific literature, there are only few evidences of lab scale devices, acting as passive radiative cooling at daytime, and remaining few degrees below ambient air. This work describes the proof of concept of a daytime passive radiative cooler, entirely developed in ENEA labs, capable to reach well 12 °C under ambient temperature. In particular, the prototypal device is an acrylic box case, filled with noble gas, whose top face is a metamaterial deposited on a metal substrate covered with a transparent polymeric film. The metamaterial here tested, obtained by means of a semi-empirical approach, is a spectrally selective coating based on low cost materials, deposited as thin films by sputtering on the metallic substrate, that emits selectively in the 8–13 µm region, reflecting elsewhere UV_VIS_NIR_IR electromagnetic radiation. The prototype during the daytime sky could reach temperatures well beyond ambient temperature. However, the proof of concept experiment performed in a bright clear June day has evidenced some limitations. A critical analysis of the obtained experimental results has done, in order to individuate design revisions for the device and to identify future metamaterial improvements.

Large-Area Growth and Stability of Monolayer Gallium Monochalcogenides for Optoelectronic Devices

Group III monochalcogenides such as GaSe and GaS have attracted considerable interest as two-dimensional (2D) alternatives to the traditional transition metal dichalcogenides. The production of large-area films as well as the long-term ambient stability remains a challenge for scalable integration of these materials into the next generation of 2D circuitry and optoelectronic devices. In this report, a simple atmospheric-pressure chemical vapor deposition method is proposed to synthesize continuous monolayers of GaSe and GaS. The proposed method utilizes commercially available precursors and does not requires vacuum-sealed ampules or exfoliation. The optimal parameters for continuous monolayer self-limited growth were determined by systematically changing the growth time, the gas flow rate, and the amount of precursors. So far, the study of bare monolayer GaSe by Raman spectroscopy has been difficult due to the very low Raman signal and a rapid laser-induced oxidation of the material. A laser-scanning method that minimizes the cumulative laser damage and allows a reasonable signal-to-noise ratio was utilized to study the time-dependent ambient stability of bare and encapsulated monolayer samples by Raman spectroscopy. Our results reveal that bare GaSe monolayers can stand up to 6 h in air before complete degradation, and encapsulation with transparent polymeric films can delay this process for few days. These results open the door to produce large-area films of monolayer group III monochalcogenides and to consider film encapsulation with different transparent polymers that could further extend the long-term durability of these ambient sensitive 2D materials.

Cellulose nanofibrils and silver nanowires active coatings for the development of antibacterial packaging surfaces

An active ink composed of cellulose nanofibrils and silver nanowires was deposited on flexible and transparent polymer films using the bar coating process, achieving controlled thicknesses ranging from 200 nm up to 2 μm. For 350 nm thick coating on polyethylene terephthalate films, high transparency (75.6% transmittance) and strong reduction of bacterial growth equal to 89.3% and 100% was noted respectively against Gram-negative Escherichia Coli and Gram-positive Staphylococcus Aureus bacteria using AATCC contact active standard test. Retained antibacterial activity was found with films produced by reverse gravure roll-to-roll process, showing the promising capability of this antibacterial solution to be deployed industrially. Finally, the same ink was also deposited on polylactic acid substrate to investigate barrier properties: for 350 nm thick coating, a reduction of 49% of oxygen transmission rate (dry conditions) and 47% reduction of water vapor transmission rate was noted, proving the enhanced barrier properties of the coatings.

Zymergen, Sumitomo launch biobased film

The California biomanufacturing start-up Zymergen and Sumitomo Chemical have developed a transparent polymer film for use in displays, touch sensors, and printable electronics. The film, Hyaline, i...

Storage of Information Using Periodic Precipitation.

In the present work, transparent flexible thin polymer films with silver patterns have been created. The resulting structures made by the printing method represent a new alternative approach for recording, protecting, and transmitting information as well as for nonlinear gradient material formation. An alphabet for process automatization was created, and an automated system for recording and reading information was developed. To protect the information, we suggest the usage of a classic XOR function: the idea of scrambling is to demonstrate the simple and clear example of coding the ITMO University logo, and the code is provided. Additionally, the resulting samples are functional gradient materials with peaks of surface plasmon resonance. In the following, automated peak decoding by UV–vis spectroscopy allows an additional physicochemical method for structure decoding.

Solution-Processed Polymeric Thin Film as the Transparent Electrode for Flexible Perovskite Solar Cells.

In the past decade, perovskite solar cells (PSCs) were arising as a new generation of low-cost solar technology for renewable energy generation. More than 25% of power conversion efficiency (PCE) was reported from PSCs on the rigid indium tin oxide (ITO)/glass electrode. However, PSCs fabricated on flexible solution-processed transparent electrodes have still been a challenge to date. In this work, we report a solution-processed transparent polymeric thin film as the electrode for flexible solution-processed PSCs. The solution-processed polymeric thin film exhibits superior optical transparency and decent electrical conductivity. As compared with a PCE of 16.60% from PSCs on the ITO/glass substrate, PSCs on the solution-processed transparent polymeric electrode/glass substrate exhibit a PCE of 13.36% and PSCs on the solution-processed transparent polymeric thin-film/polyethylene terephthalate flexible substrate possess a PCE of 10.16%. Systematic studies demonstrate that poor electrical conductivity of the solution-processed transparent polymeric electrode and serious interfacial charge carrier recombination are responsible for low PCEs. Nevertheless, our results demonstrate that we provide a facile route to develop flexible PSCs by utilization of solution-processed polymeric thin films as the transparent electrodes.

Fluorescent N-Doped Graphene Quantum Dots Embedded in Transparent Polymer Films for Photon-Downconversion Applications

In this work, we demonstrate a simple, facile, and efficient one-pot synthesis of polymer–quantum dot nanocomposite films where nitrogen-doped graphene quantum dots (N-GQDs) were homogeneously disp...

Sensitized Mechanoluminescence Design toward Mechanically Induced Intense Red Emission from Transparent Polymer Films

Mechanoresponsive polymers with intense red emission are highly desirable in view of the strong penetrability and high resolution of red luminescence. Herein we introduce the sensitized luminescence of rare-earth Eu(III) complexes into the mechanochemiluminescence from polymeric dioxetane in a covalent way. By controlling the energy-transfer process from mechanically broken dioxetane to the Eu(III) center, bright red emission from transparent poly(methyl acrylate) films was achieved for the first time. Importantly, mechanoluminescence sensitivity is greatly improved, enabling the location and timing of bond scission with high resolution. A sensitive stretchable device with the polymer film as an emissive layer was fabricated by a facile surface-engineering method, which can emit patterned red light upon deformation. This sensitized mechanoluminescence design thus expands the useful space of luminescent stress probes.

Dual roles of a transparent polymer film containing dispersed N-doped carbon dots: A high-efficiency blue light converter and UV screen

We report the synthesis of a transparent plastic material with very high performance ultraviolet (UV)-blocking and blue-light (440 nm) emission. Polyvinyl alcohol (PVA) was employed as a transparent plastic matrix that disperses N-doped carbon dots (N-CDs) prepared via hydrothermal treatment of citric acid, ethylene diamine, and HCl solution. Luminescence of these N-CDs is excitation-independent and the quantum yield (QY) is maximal at an excitation wavelength range of 350–370 nm, in the UV-A radiation segment of the solar spectrum. By encapsulating N-CDs in a polyvinyl alcohol (PVA) matrix, the absolute QY achieves 91%, which is higher than in aqueous solution. As the particle concentration increases in PVA matrix or in solution, UV absorbance increases and QY decreases. On the other hand, UV absorbance of the film is proportional to thickness with no appreciable deterioration in QY, a quality that is beneficial for UV light absorption as well as conversion into blue light. We propose that this N-CD/PVA composite is an ideal transparent plastic for UV-ray shielding, as well as being useful for blue light emission, composed only of eco-friendly nontoxic elements. The high UV absorption and strong luminescence of N-CDs are beneficial also for other applications that include anti-counterfeiting (secret inks) and greenhouse sheathing that simultaneously blocks UV-rays while generating blue light to promote plant growth.

High broadband photoconductivity of few-layered MoS2 field-effect transistors measured using multi-terminal methods: effects of contact resistance.

Among the layered two dimensional semiconductors, molybdenum disulfide (MoS2) is considered to be an excellent candidate for applications in optoelectronics and integrated circuits due to its layer-dependent tunable bandgap in the visible region, high ON/OFF current ratio in field-effect transistors (FET) and strong light-matter interaction properties. In this study, using multi-terminal measurements, we report high broadband photocurrent response (R) and external quantum efficiency (EQE) of few-atomic layered MoS2 phototransistors fabricated on a SiO2 dielectric substrate and encapsulated with a thin transparent polymer film of Cytop. The photocurrent response was measured using a white light source as well as a monochromatic light of wavelength λ = 400 nm-900 nm. We measured responsivity using a 2-terminal configuration as high as R = 1 × 103 A W-1 under white light illumination with an optical power Popt = 0.02 nW. The R value increased to 3.5 × 103 A W-1 when measured using a 4-terminal configuration. Using monochromatic light on the same device, the measured values of R were 103 and 6 × 103 A W-1 under illumination of λ = 400 nm when measured using 2- and 4-terminal methods, respectively. The highest EQE values obtained using λ = 400 nm were 105% and 106% measured using 2- and 4-terminal configurations, respectively. The wavelength dependent responsivity decreased from 400 nm to the near-IR region at 900 nm. The observed photoresponse, photocurrent-dark current ratio (PDCR), detectivity as a function of applied gate voltage, optical power, contact resistances and wavelength were measured and are discussed in detail. The observed responsivity is also thoroughly studied as a function of contact resistance of the device.

Bifacial silicon heterojunction solar cells with advanced Ag-free multi-wire metallization attached to ITO layers using new transparent conductive PAEK copolymers

Previously, we reported the synthesis and application of transparent conductive polymer (TCP) films, poly(arylene ether ketone) copolymers (co-PAEKs), for forming direct contact between wires and transparent conductive oxide (TCO) layers in silicon solar cells. The polymers have the lowest peak strain temperature (Td), which determines the contact formation temperature, of 205 °C. To utilize such TCP films in silicon heterojunction (SHJ) solar cells with amorphous silicon layers, Td should be lowered. To solve the problem in question, a number of co-PAEKs with a decreased reduced viscosity (ηred) due to a decreased molecular weight of the polymer have been synthesized in this study. It has been shown that lowering ηred from 0.56 to 0.4 dl/g markedly improves the main properties of the co-PAEKs. In particular, (i) Td decreased from 205 to 189 °C, (ii) the peel strength, determined by pulling off the wires from the polymer surface, increased from 1.69 ± 0.26 to 3.55 ± 0.84 N/mm, and (iii) the resistivity of the wire/TCP/ITO (In2O3:Sn) contact, ρC, dropped from 1.20 to 0.67 mΩ cm2. At the same time, the optical properties of the copolymers remained unchanged. We have fabricated bifacial rear junction SHJ solar cells based on a ITO/(n)α-Si:H/(i)α-Si:H/(n)Cz-Si/(i)α-Si:H/(p)α-Si:H/ITO structure, with wire contact grids attached to the ITO layers using co-PAEK films. A solar cell produced using the co-PAEK film with the lowest reduced viscosity had an efficiency under front/rear illumination of 19.6%/18.4%. At 1-sun front illumination and 20/50% of 1-sun rear illumination, the equivalent efficiency is equal to 23.3%/28.8%.