High-Performance and Rapid-Response Electrical Heaters Derived from Cellulose Nanofiber/Silver Nanowire Nanopapers for Portable Thermal Management

Caffeic-Acid-Functionalized MWCNTs and PEDOT:PSS Formed Composite Flexible Films with "Reinforced Concrete" Structure for Electrical Heating and EMI Shielding

Nowadays, flexible multifunctional composites are attracting much attention and are practically being used in various emerging electronic devices. However, most composites suffer from the disadvantages of high loadings of conductive fillers, complicated preparation processes, and low energy conversion efficiency. In this article, Caffeic acid-modified multiwalled carbon nanotubes (C-MWCNTs)/poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS)/polyimide (PI) composite films (CPFs) were prepared using a simple layer-by-layer deposition method. The "reinforced concrete" structure of the C-MWCNTs/PEDOT:PSS layer ensures high electrical conductivity of the film, while the PI layer provides excellent mechanical properties (72.69 MPa). The composite film exhibits excellent electrothermal response and thermal stability up to approximately 125 °C at 5 V. In addition, the good conductivity of the film provides its electromagnetic shielding effectiveness (32.69 dB). With these advantages, we expect that flexible CPFs will be widely utilized in wearable devices, electromagnetic interference (EMI) shielding applications, and thermal management of personal or electronic devices.

Improvement of electrothermal and photothermal properties of ultra-thin graphite film on oxygen plasma-treated polyimide substrate

Graphene and its derivatives are widely used in the field of energy conversion and management due to their excellent physical and chemical properties. In this paper, ultra-thin graphite film (GF) with thickness of 100-150 nm prepared by chemical vapor deposition was transferred to oxygen plasma-treated polyimide (PI) substrate as flexible heating film. The electrothermal and photothermal properties of GF on PI substrates with different treatment time were studied. The experimental results show that the PI substrate pretreated by oxygen plasma can change the surface morphology of GF, increase its electrical conductivity and light absorption capacity, and significantly improve the electrothermal and photothermal properties of GF heater. Under the low applied voltage of 5 V (power density of 0.81 W cm-2), the surface temperature of GF on 40 min plasma-treated PI substrate can rise to 250 °C, which is nearly 50 °C higher than that of GF on untreated PI substrate. When 100 nm thick commercial multilayer graphene film (MLG) is used, plasma-treated PI substrate can increase the electric heating temperature of MLG by 70 °C. In terms of photothermal performance, the surface temperature of GF on 50 min plasma-treated PI substrate can reach 73 °C under one Sun irradiation, which is 8 °C higher than that on untreated substrate. The experimental results are in good agreement with the simulation research. Our strategy has important implications for the development of efficient and energy-saving graphene/graphite-based heating films for advanced electrothermal and photothermal conversion devices.

Hydrated alginate polysaccharide fabrics grafted with sliver nanocrystals for wearable thermal and health management

The creation of functional components with precise chemistries on carbohydrate polymers is of great significance for future wearable biomedicine and health management. Among various carbohydrate polymers, marine polysaccharide featured with antimicrobial, biodegradable and biocompatible properties is an ideal platform while the water-swelling nature makes it difficult to form stable interface. Here, well-dispersed silver nanoparticles have been in-situ assembled on hydrated alginate fabric (AF), involving chemical absorption of Ag ions and in-situ reduction of conductive Ag layer. Owing to the stable complex formed between Ag ions and carboxyl groups, the Ag-grafted AF exhibits superior Joule heating capability, including low operating voltage (1-3 V), high saturation temperature (63 °C), rapid response time (25 s) and outstanding durability against harsh conditions. Furthermore, the Ag-grafted AF demonstrates noticeable inhibition against E. coli and S. aureus as compared with the pristine AF. This work provides a rational strategy for the functionalization of hydrated polysaccharide and enables wearable thermotherapy devices for human health management.

A Janus membrane doped with carbon nanotubes for wet-thermal management

In a human skin-fibrous fabric-external environment, fibrous materials, as the "second skin" of the human body, provide comfort against the wet and heat effectively. Fibrous materials protect human health and guarantee work efficiency in various outdoor or inner scenes. Personal wet-thermal management based on fibrous materials can regulate comfort in a facile manner with low or zero energy consumption, which has become a potential development area. However, realizing synergistic management of the wet and heat effectively and conveniently is a challenge in the development and production of fibrous materials. We designed and fabricated a Janus fibrous membrane composed of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA)-modified hydrophobic cotton gauze and electrospun carbon nanotubes (CNTs)-doped cellulose acetate (CA) hydrophilic fibrous membrane. Taking advantage of asymmetric wettability along its thickness direction, the Janus fibrous membrane, acting as a "liquid diode", could transport sweat/moisture from human skin to the external environment unidirectionally, which endowed a dry surface on human skin, avoiding "stickiness", and realizing wet management. Doped CNTs had good photothermal-conversion capacity, so the Janus membrane exhibited excellent heating capacity for passive radiation, so excellent synergistic wet-thermal management was obtained. The Janus membrane could be a candidate for diverse applications of fibrous membranes. Our data provide new ideas for the design and fabrication of fibrous membranes with remarkable wet-thermal management.

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.

Dual-asymmetrically selective interfaces-enhanced poly(lactic acid)-based nanofabric with sweat management and switchable radiative cooling and thermal insulation

All-weather personal thermal regulation has far been challenged by variable environments especially the regulatory failure caused by highly-dense solar radiation, low environmental radiation and the fluctuated epidermal moisture in different seasons. Herein, from the design of interface selectivity, dual-asymmetrically optical and wetting selective polylactic acid-based (PLA) Janus-type nanofabric is proposed to achieve on-demand radiative cooling and heating as well as sweat transportation. Hollow TiO₂ particles are introduced in PLA nanofabric causing high interface scattering (∼99%) and infrared emission (∼91.2%) as well as surface hydrophobicity (CA > 140°). The strictly optical and wetting selectivity help achieve ∼12.8℃ of net cooling effect under > 1500 W/m² of solar power and ∼5℃ of cooling advantage higher than cotton fabric and sweat resistance simultaneously. Contrarily, the semi-embedded Ag nanowires (AgNWs) with high conductivity (0.245 Ω/sq) endows the nanofabric with visible water permeability and excellent interface reflection for thermal radiation from body (>65%) thus causing ∼7℃ of thermal shielding. Through simple interface flipping, synergistical cooling-sweat reducing and warming-sweat resisting can be achieved to satisfy the thermal regulation in all weather. Compared with conventional fabrics, multi-functional Janus-type passive personal thermal management nanofabrics would be of great significance to achieve the personal health maintenance and energy sustainability.