Novel stretchable thermochromic transparent heaters designed for smart window defroster applications by spray coating silver nanowire

Micro/nanofabrication of heat management materials for energy-efficient building facades

Advanced building facades, which include windows, walls, and roofs, hold great promise for reducing building energy consumption. In recent decades, the management of heat transfer via electromagnetic radiation between buildings and outdoor environments has emerged as a critical research field aimed at regulating solar irradiation and thermal emission properties. Rapid advancements have led to the widespread utilization of advanced micro/nanofabrication techniques. This review provides the first comprehensive summary of fabrication methods for heat management materials with potential applications in energy-efficient building facades, with a particular emphasis on recent developments in fabrication processing and material property design. These methods include coating, vapor deposition, nanolithography, printing, etching, and electrospinning. Furthermore, we present our perspectives regarding their advantages and disadvantages and our opinions on the opportunities and challenges in this field. This review is expected to expedite future research by providing information on the selection, design, improvement, and development of relevant fabrication techniques for advanced materials with energy-efficient heat management capabilities.

Capillary Force-Induced Graphene Spontaneous Transfer and Encapsulation of Silver Nanowires for Highly-Stable Transparent Electrodes

Silver nanowires (NWs) (AgNWs) have emerged as the most promising conductive materials in flexible optoelectronic devices owing to their excellent photoelectric properties and mechanical flexibility. It is widely acknowledged that the practical application of AgNW networks faces challenges, such as high surface roughness, poor substrate adhesion, and limited stability. Encapsulating AgNW networks with graphene has been recognized as a viable strategy to tackle these issues. However, conventional methods like self-assembly reduction-oxidation or chemical vapor deposition often yield graphene protective layers with inherent defects. Here, we propose a novel one-step hot-pressing method containing ethanol solution that combines the spontaneous transfer and encapsulation process of rGO films onto the surface of the AgNWs network, enabling the preparation of flexible rGO/AgNWs/PET (reduced graphene oxide/silver NWs/polyethylene terephthalate) electrodes. The composite electrode exhibits outstanding photoelectric properties (T ≈ 88%, R ≈ 6 Ω sq-1) and possesses a smooth surface, primarily attributed to the capillary force generated by ethanol evaporation, ensuring the integrity of the rGO delamination process on the original substrate. The capillary force simultaneously promotes the tight encapsulation of rGO and AgNWs, as well as the welding of the AgNWs junction, thereby enhancing the mechanical stability (20,000 bending cycles and 100 cycles of taping tests), thermal stability (∼30 °C and ∼25% humidity for 150 days), and environmental adaptability (100 days of chemical attack) of the electrode. The electrode's practical feasibility has been validated by its exceptional flexibility and cycle stability (95 and 98% retention after 5000 bending cycles and 12,000 s long-term cycles) in flexible electrochromic devices.

MoO3 nanowire growth on VO2/WO3 for thermochromic applications

This study explores the structural, electronic, and optical properties of sandwich-structured thin films composed of WO3, MoWO3, and MoO3 as window layers on VO2/WO3via a physical vapor deposition method. Morphological analysis demonstrates the evolution of distinct nanowires, offering insights into the lattice strain of the VO2 layer toward high-performance thermochromatic devices. Temperature-dependent sheet resistivity is investigated, showcasing significant improvements in conductivity for samples with MoO3 as a window layer. The electrical and optical properties of the MoO3/VO2/WO3 device showed a phase transition temperature (Tc) of 36.8 °C, a transmittance luminous (Tlum) of 54.57%, and a solar modulation ability (ΔTsol) of 12.43. This comprehensive analysis contributes to understanding the growth of nanowires on multi-layered thin films, offering valuable insights into potential applications in bright windows.

Super-strong and high-performance electrical film heater derived from silver nanowire/aligned bacterial cellulose film

High-performance electrical Joule heaters with high mechanical properties, low driving voltage, rapid response, and flexibility are highly desirable for portable thermal management. Herein, by using aligned bacterial cellulose (BC) and silver nanowire (AgNW), we fabricated a novel film heater based on Joule heating phenomena. The aligned BC film prepared by stretching BC hydrogel and hot-pressing drying technology showed outstanding mechanical properties and flexibility. The ultrahigh strength of up to 1018 MPa and the toughness of 20 MJ/m3 were obtained for the aligned BC film with 40% wet-stretching (BC-40). In addition, the aligned BC film could be folded into desirable shapes. The AgNW was spray-coated on the surface of aligned BC-40 film and then covered with polydimethylsiloxane to form a P@AgNW@BC heater. P@AgNW@BC heater showed excellent conductivity, which endowed the film heater with an outstanding Joule heating performance. P@AgNW@BC heater could reach ~ 98 ℃ at a very low driving voltage of 4 V with a rapid heating response (13 s) and long-term temperature stability. The P@AgNW@BC heater with such an outstanding heating performance can be used as a flexible heating device for different applications in daily life like deicing/defogging device, wearable thermotherapy, etc.Affiliations: Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.yes, we confirmed the affiliations are correct. Article title: Kindly check and confirm the edit made in the article title.Thanks, the title is no problem.

Functional Materials and Innovative Strategies for Wearable Thermal Management Applications

Highlights

This article systematically reviews the thermal management wearables with a specific emphasis on materials and strategies to regulate the human body temperature. Thermal management wearables are subdivided into the active and passive thermal managing methods. The strength and weakness of each thermal regulatory wearables are discussed in details from the view point of practical usage in real-life.

Abstract

Thermal management is essential in our body as it affects various bodily functions, ranging from thermal discomfort to serious organ failures, as an example of the worst-case scenario. There have been extensive studies about wearable materials and devices that augment thermoregulatory functionalities in our body, employing diverse materials and systematic approaches to attaining thermal homeostasis. This paper reviews the recent progress of functional materials and devices that contribute to thermoregulatory wearables, particularly emphasizing the strategic methodology to regulate body temperature. There exist several methods to promote personal thermal management in a wearable form. For instance, we can impede heat transfer using a thermally insulating material with extremely low thermal conductivity or directly cool and heat the skin surface. Thus, we classify many studies into two branches, passive and active thermal management modes, which are further subdivided into specific strategies. Apart from discussing the strategies and their mechanisms, we also identify the weaknesses of each strategy and scrutinize its potential direction that studies should follow to make substantial contributions to future thermal regulatory wearable industries.

Batch Nanofabrication of Suspended Single 1D Nanoheaters for Ultralow-Power Metal Oxide Semiconductor-Based Gas Sensors

The demand for power-efficient micro-and nanodevices is increasing rapidly. In this regard, electrothermal nanowire-based heaters are promising solutions for the ultralow-power devices required in IoT applications. Herein, a method is demonstrated for producing a 1D nanoheater by selectively coating a suspended pyrolyzed carbon nanowire backbone with a thin Au resistive heater layer and utilizing it in a portable gas sensor system. This sophisticated nanostructure is developed without complex nanofabrication and nanoscale alignment processes, owing to the suspended architecture and built-in shadow mask. The suspended carbon nanowires, which are batch-fabricated using carbon-microelectromechanical systems technology, maintain their structural and functional integrity in subsequent nanopatterning processes because of their excellent mechanical robustness. The developed nanoheater is used in gas sensors via user-designable localization of the metal oxide semiconductor nanomaterials onto the central region of the nanoheater at the desired temperature. This allows the sensing site to be uniformly heated, enabling reliable and sensitive gas detection. The 1D nanoheater embedded gas sensor can be heated immediately to 250 °C at a remarkably low power of 1.6 mW, surpassing the performance of state-of-the-art microheater-based gas sensors. The presented technology offers facile 1D nanoheater production and promising pathways for applications in various electrothermal devices.

Reaction-Based Scalable Inorganic Patterning on Rigid and Soft Substrates for Photovoltaic Roofs with Minimal Optical Loss and Sustainable Sunlight-Driven-Cleaning Windows

Recently developed fabrication methods for inorganic patterns (such as laser printing and optical lithography) can avoid some patterning processes conducted by conventional etching and lithography (such as substrate etching and modulation) and are thereby useful for applications in which the substrates and materials must not be damaged during patterning. Simultaneously, it is also necessary to develop facile and economical methods producing inorganic patterns on various substrates without requiring a special apparatus while attaining the above-mentioned advantages. The present study proposes a reaction-based method for fabricating inorganic patterns by immersing substrates coated with a colloidal nanosheet into an aqueous solution containing inorganic precursors. Silica and TiO₂ patterns spontaneously developed during the conversion of each inorganic precursor. These patterns were successful on rigid and flexible substrates. We fabricated these patterns on a wafer-sized silicon and large flexible poly(ethylene terephthalate) film, suggesting the scalability. We fabricated a biomimetic pattern on both sides of a glass window, as a photovoltaic roof, for minimal optical losses to maximally present photovoltaic effects of a solar cell. The TiO₂ pattern on glass window exhibits sustainable sunlight-driven-cleaning activity for contaminants. The method could provide a platform for economical high-performance inorganic patterns for energy, environmental, electronics, and other areas.

Advances in constructing silver nanowire-based conductive pathways for flexible and stretchable electronics

With their soaring technological demand, flexible and stretchable electronics have attracted many researchers' attention for a variety of applications. The challenge which was identified a decade ago and still remains, however, is that the conventional electrodes based on indium tin oxide (ITO) are not suitable for ultra-flexible electronic devices. The main reason is that ITO is brittle and expensive, limiting device performance and application. Thus, it is crucial to develop new materials and processes to construct flexible and stretchable electrodes with superior quality for next-generation soft devices. Herein, various types of conductive nanomaterials as candidates for flexible and stretchable electrodes are briefly reviewed. Among them, silver nanowire (AgNW) is selected as the focus of this review, on account of its excellent conductivity, superior flexibility, high technological maturity, and significant presence in the research community. To fabricate a reliable AgNW-based conductive network for electrodes, different processing technologies are introduced, and the corresponding characteristics are compared and discussed. Furthermore, this review summarizes strategies and the latest progress in enhancing the conductive pathway. Finally, we showcase some exemplary applications and provide some perspectives about the remaining technical challenges for future research.

Human Skin-Inspired Electrospun Patterned Robust Strain-Insensitive Pressure Sensors and Wearable Flexible Light-Emitting Diodes

Wearable skin-inspired electronic skins present remarkable outgrowth in recent years because their promising comfort device integration, lightweight, and mechanically robust durable characteristics led to significant progresses in wearable sensors and optoelectronics. Wearable electronic devices demand real-time applicability and factors such as complex fabrication steps, manufacturing cost, and reliable and durable performances, severely limiting the utilization. Herein, we nominate a scalable solution-processable electrospun patterned candidate capable of forming ultralong mechanically robust nano-microdimensional fibers with higher uniformity. Nanofibrous patterned substrates present surface energy and silver nanoparticle crystallization shifts, contributing to strain-sensitive and -insensitive conductive electrodes (10 000 cycles of 50% strain). Synergistic robust stress releasing and durable electromechanical behavior engenders stretchable durable health sensors, strain-insensitive pressure sensors (sensitivity of ∼83 kPa^-1 and 5000 durable cycles), robust alternating current electroluminescent displays, and flexible organic light-emitting diodes (20% improved luminescence and 300 flex endurance of 2 mm bend radius).

Advances in Flexible Metallic Transparent Electrodes

Transparent electrodes (TEs) are pivotal components in many modern devices such as solar cells, light-emitting diodes, touch screens, wearable electronic devices, smart windows, and transparent heaters. Recently, the high demand for flexibility and low cost in TEs requires a new class of transparent conductive materials (TCMs), serving as substitutes for the conventional indium tin oxide (ITO). So far, ITO has been the most used TCM despite its brittleness and high cost. Among the different emerging alternative materials to ITO, metallic nanomaterials have received much interest due to their remarkable optical-electrical properties, low cost, ease of manufacturing, flexibility, and widespread applicability. These involve metal grids, thin oxide/metal/oxide multilayers, metal nanowire percolating networks, or nanocomposites based on metallic nanostructures. In this review, a comparison between TCMs based on metallic nanomaterials and other TCM technologies is discussed. Next, the different types of metal-based TCMs developed so far and the fabrication technologies used are presented. Then, the challenges that these TCMs face toward integration in functional devices are discussed. Finally, the various fields in which metal-based TCMs have been successfully applied, as well as emerging and potential applications, are summarized.

Transparent and flexible passivation of MoS2/Ag nanowire with sputtered polytetrafluoroethylene film for high performance flexible heaters

We demonstrated highly transparent and flexible polytetrafluoroethylene (PTFE) passivation for the MoS2/Ag nanowire (Ag NW) electrodes used in thin film heaters (TFHs). The electrical, optical, and mechanical properties of PTFE coated MoS2/Ag NW electrode were compared to the bare MoS2/Ag NW electrode to demonstrate effective passivation of the sputtered PTFE films before and after the 85 °C-85% temperature-relative humidity environment test. In addition, we investigated the performances of TFHs with PTFE/MoS2/Ag NW as a function of PTFE thickness from 50 to 200 nm. The saturation temperature (87.3 °C) of TFHs with PTFE/MoS2/Ag NW electrode is higher than that (61.3 °C) of TFHs with bare MoS2/Ag NW, even after the 85 °C-85% temperature-relative humidity environment test, due to effective passivation of the PTFE layer. This indicates that transparent PTFE film prepared by sputtering process provides effective thin film passivation for the two-dimensional (2D) MoS2 and Ag NW hybrid electrode against harsh environment condition.

Recent Progress in Conducting Polymer Composite/Nanofiber-Based Strain and Pressure Sensors

The Conducting of polymers belongs to the class of polymers exhibiting excellence in electrical performances because of their intrinsic delocalized π- electrons and their tunability ranges from semi-conductive to metallic conductive regime. Conducting polymers and their composites serve greater functionality in the application of strain and pressure sensors, especially in yielding a better figure of merits, such as improved sensitivity, sensing range, durability, and mechanical robustness. The electrospinning process allows the formation of micro to nano-dimensional fibers with solution-processing attributes and offers an exciting aspect ratio by forming ultra-long fibrous structures. This review comprehensively covers the fundamentals of conducting polymers, sensor fabrication, working modes, and recent trends in achieving the sensitivity, wide-sensing range, reduced hysteresis, and durability of thin film, porous, and nanofibrous sensors. Furthermore, nanofiber and textile-based sensory device importance and its growth towards futuristic wearable electronics in a technological era was systematically reviewed to overcome the existing challenges.

Highly efficient patterning technique for silver nanowire electrodes by electrospray deposition and its application to self-powered triboelectric tactile sensor

A patterned transparent electrode is a crucial component of state-of-the-art wearable devices and optoelectronic devices. However, most of the patterning methods using silver nanowires (AgNWs), which is one of the outstanding candidate materials for the transparent electrode, wasted a large amount of unused AgNWs during the patterning process. Here, we report a highly efficient patterning of AgNWs using electrospray deposition with grounded electrolyte solution (EDGE). During electrospray deposition, a patterned electrolyte solution collector attracted AgNWs by strong electrostatic attraction and selectively deposited them only on the patterned collector, minimizing AgNW deposited elsewhere. The enhanced patterning efficiency was verified through a comparison between the EDGE and conventional process by numerical simulation and experimental validation. As a result, despite the same electrospray deposition conditions for both cases except for the existence of the electrolyte solution collector, the coverage ratio of AgNWs fabricated by the EDGE process was at least six times higher than that of AgNWs produced by the conventional process. Furthermore, the EDGE process provided high design flexibility in terms of not only the material of the substrate, including a polymer and a ceramic but also the shape of the substrate, including a 2D flat and 3D curved surface. As an application of the EDGE process, a self-powered touch sensor exploiting the triboelectric effect was demonstrated. Thus, the EDGE process would be utilized in further application in wearable or implantable devices in the field of biomedicine, intelligent robots, and human-machine interface.

Copper micromesh-based lightweight transparent conductor with short response time for wearable heaters

Thickness-controlled transparent conducting films (TCFs) were fabricated by transfer printing a 100 nm thick Cu micromesh structure onto poly(vinyl alcohol) (PVA) substrates of different thicknesses (~ 50, ~ 80, and ~ 120 μm) to develop a lightweight transparent wearable heater with short response time. The Cu mesh-based TCF fabricated on a ~ 50 µm thick PVA substrate exhibited excellent optical and electrical properties with a light transmittance of 86.7% at 550 nm, sheet resistance of ~ 10.8 Ω/sq, and figure-of-merit of approximately 236, which are comparable to commercial indium tin oxide film-based transparent conductors. The remarkable flexibility of the Cu mesh-based TCF was demonstrated through cyclic mechanical bending tests. In addition, the Cu mesh-based TCF with ~ 50 μm thick PVA substrate demonstrated a fast Joule heating performance with a thermal response time of ~ 18.0 s and a ramping rate of ~ 3.0 ℃/s under a driving voltage of 2.5 V. Lastly, the reliable response and recovery characteristics of the Cu mesh/PVA film-based transparent heater were confirmed through the cyclic power test. We believe that the results of this study is useful in the development of flexible transparent heaters, including lightweight deicing/defogging films, wearable sensors/actuators, and medical thermotherapy pads.

Deep-Sintered Copper Tracks for Thermal Oxidation Resistance Using Large Pulsed Electron Beam

Thermal oxidation resistance is an important property in printed electronics for sustaining electrical conductivity for long time and/or under harsh environments such as high temperature. This study reports the fabrication of copper nanoparticles (CuNPs)-based conductive tracks using large pulsed electron beam (LPEB) by irradiation on CuNPs to be sintered. With an acceleration voltage of 11 kV, the LPEB irradiation induced deep-sintering of CuNPs so that the sintered CuNPs exhibited bulk-like electrical conductivity. Consequently, the sintered Cu tracks maintained high electrical conductivity at 220 °C without using any thermal oxidation protection additive, such as silver, carbon nanotube, and graphene. In contrast, the films irradiated with an acceleration voltage of 8 kV and irradiated by intense pulsed light (IPL) showed fast oxidation characteristics and a corresponding reduction of electrical conductivities under high temperatures owing to a thin sintered layer. The performance of highly thermal oxidation-resistant Cu films sintered by LPEB irradiations was demonstrated through the device performance of a Joule heater.

Soft, Stretchable, and Pneumatically Triggered Thermochromic Optical Filters with Embedded Phosphorescence

Phosphorescence is commonly used in nature to communicate using light. There are many ways to activate phosphorescence, including UV light, heat, and mechanical forces, but there are few methods to control phosphorescence once activated. Here, we present soft composite devices-which we call "optical filters"-for controlling the release of light by phosphorescence within a stretchable matrix. The filters consist of liquid metal wires, phosphorescent particles, and thermochromic pigments embedded in an elastomeric matrix. UV light initially activates the phosphorescence of rare-earth long-lasting luminescent particles. At room temperature, the thermochromic pigments block the phosphorescence from leaving the matrix. However, Joule heating of the liquid metal can change the opacity of the thermochromic pigments, which tunes the color, intensity, and wavelength of phosphorescence that exits the composite. In addition, the resistance of the liquid metal wires changes with physical deformation, thereby converting mechanical forces (strain, compression, and pneumatic inflation) into an optical response. Controlled phosphorescence, combined with the electrical conductivity of the liquid metal and the overall soft matrix, enables potential applications as an electronic skin for soft robotics, stretchable electronics, and prosthetics.

Effect of Coating Process on Performance of Reversible Thermochromic Waterborne Coatings for Chinese Fir

The effect of the coating process on the properties of reversible thermochromic waterborne coating on the surface of Chinese fir was examined. The results demonstrated that the most critical process parameter affecting the color difference and gloss of the coating was the way of adding thermochromic ink. The coating process had little influence on the adhesion, impact resistance adding, liquid resistance, and original properties of the coating. There was no obvious gloss variation in the coating under different coating processes. For the (3+3) layered coatings, when the thermochromic ink was added to the topcoats, the discoloration performance was the most obvious and the comprehensive performance of coating was better. Meanwhile, the gloss was 55.6%, the adhesion grade was grade 0, the impact resistance was 5.0 kg·cm, the liquid resistance grade of the coating to sodium chloride, ethanol and detergent was grade 1, and the liquid resistance grade to red ink was grade 3. The discoloration performance of the coating was stable under the conditions of aging and time change. This study provides new insight into preparing thermochromic intelligent waterborne wood coatings with potential practical applications on Chinese fir wood surfaces, and also lays a foundation for its application in furniture engineering.

Light Down-Converter Based on Luminescent Nanofibers from the Blending of Conjugated Rod-Coil Block Copolymers and Perovskite through Electrospinning

We demonstrated a novel strategy for the preparation of light down-converter by combining rod-coil block copolymers with perovskite quantum dots (QDs) through electrospinning. Reports have shown that polymer deformability can be enhanced by incorporating a soft segment and controlled by varying the rod/coil ratio. Therefore, we first synthesized the rod-coil block copolymer through the click reaction of polyfluorene (PF) and poly(n-butyl acrylate) (PBA). Next, the CsPbBr3@PF8k-b-PBA12k composite fibers were fabricated by blending perovskite through electrospinning. Optical spectral evidence demonstrated the success of the strategy, as light down-converters were prepared through the controlled variance of QD/polymer ratios to achieve tunable color and stretchability. This result reveals the potential of using rod-coil block copolymers to fabricate color-tunable perovskite light down-converters.