Electrothermal Film Research Articles

A Novel Variable Stiffness and Tunable Bending Shape Soft Robotic Finger Based on Thermoresponsive Polymers

In this study, a soft robotic finger with variable stiffness and tunable bending shape capability is proposed. The finger employs shape memory polymers (SMP) as the variable stiffness element and polyimide (PI) electrothermal films as the flexible heaters for segmental heating. SMP and PI electrothermal films constitute the variable stiffness structure. The SMP part exhibits a reversible transition from glass state to rubber state during the heating/cooling process. The whole transition process results in an elastic modulus range of three orders of magnitude. The finger can obtain multiple bending shapes and adapt to the outer contours of diverse objects because of the segmental stiffness modulation capability of the variable stiffness structure. Supercoiled polymer artificial muscles (SCPAMs) are used as actuators for the finger. SMPs and SCPAMs are thermoresponsive and can be activated by thermal heating with electricity, making the whole finger structure compact. Experimental results show that the stiffness of the finger at room temperature (25 °C) is 10.54 times that at 70 °C when the actuators are on. The performance of the finger is further validated via the sequential motion demonstration and grasping tests with variable stiffness and bending shape control capabilities, showing the proposed design’s potential in soft grippers and robotic design.

Multi-scale GO/CNT/AlN nanocomposites for high-performance flexible electrothermal film heaters

A novel high-performance flexible heater with a high heating rate through screen printing is proposed based on multi-scale nanocomposites comprised of multi-layer graphene oxide (ML-GO), carbon nanotubes (CNT) and aluminum nitride (AlN).

Micro–nano dual-scale embedded graphene/Ag architectures for flexible low-voltage-driven transparent electrothermal films

Micro–nano dual-scale embedded graphene/Ag architectures are designed for fabricating high-performance flexible transparent electrodes, thus realizing low-voltage-driven transparent electrothermal films.

Modified carbon nanotubes/polyvinyl alcohol composite electrothermal films

Carbon nanomaterials are ideal materials for electrothermal applications because of their superior thermal conductivity, electrical conductivity, and mechanical properties. Electrothermal composites with excellent performance should have the characteristics of rapid temperature response, uniform heating temperature distribution, and good thermal stability after prolonged heating. However, for previously prepared electrothermal composites still have some shortcomings such as long temperature response time, uneven temperature distribution and poor thermal stability after long time heating. In this study, the composite electrothermal films with excellent performances were obtained by a layer-by-layer deposition approach, which were synthesized by pouring epigallocatechin gallate-functionalized multi-walled carbon nanotubes (E-MWCNTs) into a polytetrafluoroethylene mold and subsequently curing the polyvinyl alcohol (PVA) solution on the CNT layer. The electro-heating behavior of composite electrothermal film with different content and size was investigated by applying various voltages. They exhibit excellent electrothermal property, that is, a rapid temperature response, which can reach the steady-state temperature (TMAX) within 90 s. In addition, the maximum temperature can reach about 140 °C at 12 V. It was observed that the temperature of the composite electrothermal film has no significant change during the cycle tests of various voltages and 5 h aging time. According to the results of the experiment, the electrothermal properties of the composite electrothermal films are affected by the content of multi-walled carbon nanotubes (MWCNTs) and the applied voltage, which means that we can achieve accurate control of its properties by adjusting the content of MWCNTs and the applied voltage. Moreover, we have great expectations that these composite electrothermal films will have broad prospects for thermal management in wearable applications and electro-devices.

Multifunctional composite polyvinyl alcohol films prepared with economic conductive carbon black and MXene microcapsuled APP

Multifunctional flexible electrothermal film has the advantages of high heating efficiency, good heat dissipation conditions, high surface power density, flame retardant and so on, which is widely used in construction, medical, agriculture, military, household products and other fields. In this work, a new type of economical, environmentally friendly, fire-safe electrothermal and electromagnetic (EMI) shielding composite film with PVA as the binder was prepared by introducing MXene-microcapsuled ammonium polyphosphate (MAPP) and conductive carbon black (CCB). After the addition of MAPP as a synergist, the conductivity of the PVA/CCB/MAPP films was increased by 66.5%. In addition, it shows excellent EMI shielding effectiveness (47.1 dB, 0.4 mm thickness). Furthermore, the PVA/CCB/MAPP thin film can reach 100 °C at an applied voltage of 12 V. These results also show good cycling and long-term electrothermal performance. In the combustion performance test, compared with PVA-0, the PVA/CCB/MAPP film had an 86.6% lower pHRR, and the THR was decreased by 59.9%. The surface temperatures of the wood sticks and FPUF reached 79.9 °C and 62.1 °C, respectively, showing excellent electrothermal effects. The PVA/CCB/MAPP film can also completely inhibit the combustion of FPUF. In short, the study offers a novel method to gain eco-friendly, fire safety and EMI shielding electrothermal films that can be coated on different substrates.

Infrared Radiation of Graphene Electrothermal Film Triggered Alpha and Theta Brainwaves

The alpha and theta frequency brainwave activity in electroencephalogram (EEG) signal is proven to correlate with attention, inhibitory processes, memory, perceptual abilities, and sleep. The decreasing of brainwaves is demonstrated to be the reason of aging and even Alzheimer's disease, so triggering alpha and theta brainwave activity may bring positive behavioral modifications such as promoting health care and a quick sleep. Herein, it is discovered that infrared radiation from multilayer graphene electrothermal film can obviously promote the appearance of alpha and theta brainwaves in the human brain. In particular, the occurrence frequency and duration time of the alpha and theta waves in EEG can be effectively enhanced up to 2.3/2.9 and 3.0/4.1 times, respectively. The comparative effect of different working temperatures and heating materials is systematically investigated, indicating efficient infrared radiation from the multilayer graphene electrothermal film, which coincides with the human‐body thermal‐radiation wavelength range from 7 to 14 μm, may be the main mechanism for this enhancement. The multilayer graphene film electrical heater represents a convenient and surprising way for triggering alpha and theta brainwaves, which has many potential applications in the area of enlarged healthcare requirements.

Establishment and experimental verification of 3D model of electrothermal film heating room

Based on turbulence simulation and thermal radiation theory, the physical and mathematical model of electric heating film heating room is established, the appropriate grid form is selected to be meshed, reasonable boundary conditions are set, and the grid independence test is carried out and combing with the experimental test results, the correctness of the model is verified. The results show that the simulation results are consistent with the experimental results, and the maximum error is 13%, indicating that the simulation model is accurate enough. The simulation model provides ideas for related research in the field of electrothermal film heating.

Absorption-Dominant, Low-Reflection Multifunctional Electromagnetic Shielding Material Derived from Hydrolysate of Waste Leather Scraps.

High-performance flexible conductive films are highly promising for the development of wearable devices, artificial intelligence, medical care, etc. Herein, a three-step procedure was developed to produce electromagnetic interference (EMI) shielding, Joule heating, and a hydrophobic nanofiber film based on hydrolysate of waste leather scraps (HWLS): (i) electrospinning preparation of the HWLS/polyacrylonitrile (PAN)/zeolitic imidazolate framework-67 (ZIF-67) nanofiber film, (ii) carbonization of the HWLS/PAN/ZIF-67 nanofiber film, and (iii) coating of the carbon nanofiber@cobalt (Co@CNF) nanofiber film with perfluorooctyltriethoxysilane (POTS). The X-ray diffraction results showed that metal nanoparticles and amorphous carbon had obvious peaks. The micromorphology results showed that metal nanoparticles were coated with carbon nanofibers. The conductivity and shielding efficiency of the carbon nanofiber film with 250 μm thickness could reach 45 S/m and 49 dB, respectively, and absorption values (A > 0.5) were higher than reflection (R) values for the Co@CNF nanofiber film, which indicated that the contribution of absorption loss was more significant than that of reflection loss. Ultrafast electrothermal response performances were also achieved, which could guarantee the normal functioning of films in cold conditions. The water contact angle of the Co@CNF@POTS nanofiber film was ∼151.3°, which displayed a self-cleaning property with water-proofing and antifouling. Absorption-dominant and low-reflection EMI shielding and electrothermal films not only showed broad application potential in flexible wearable electronic devices but also provided new avenues for the utilization of leather solid waste.

High‐Performance Electrothermal Film Based on Laser‐Induced Graphene

Herein, flexible and robust heaters are proposed based on laser‐induced graphene (LIG) fabricated photothermally on polyimide (PI) substrates. The heaters are precisely defined by a computer numerical control (CNC) platform‐driven laser diode with a one‐step process. The electrothermal performance of the heaters can be adjusted by tuning the laser driving speed in a certain range under a given input power. The fabricated heater shows a high saturation temperature (270 °C), the fast response time (10 s), and satisfactory convective heat‐transfer coefficient (42 W m−2 °C−1). Simultaneously, the developed heaters demonstrate excellent flexibility, robust adhesion, and good long‐time stability. The experimental results pave the way for high‐performance, environmentally friendly, robust, and flexible heaters.

Flexible nanocomposite electrothermal films based on carbon nanotubes and waterborne polyurethane with high reliability, stretchability and low-temperature performance for wind turbine blade deicing

Since the “net-zero” goal was proposed, wind power has been developed rapidly in recent years. Due to its large-scale installations in cold regions, the icing of wind turbine blades is currently one of the main limitations for efficient operation. In response to this issue, a highly reliable, flexible, stretchable, and lightweight in-situ deicing heating system based on the CNT/WPU nanocomposite films was developed. The CNT/WPU thin films were fabricated by the roll-to-roll gap-coating and hot-pressing process leading to as-prepared CNT/WPU film heaters have so outstanding reliability that they can withstand 100,000 times 240° bending with the resistance fluctuation of 3.17 %, and the repeated stretching of 2.0 % strain in the length direction without any impact on their temperature distribution, and even the weak impact with 10 % strain. The films may have promising potential applications in various curved surface heating with strict requirements on reliability in the future.

CuCl2-doped graphene-based screen printing conductive inks

The preparation of graphene-based conductive inks and their application in the field of flexible electronics have been extensively studied. However, improving the conductivity of the printed patterns always induces the neglect of the rheological properties of the graphene-based conductive inks or the mechanical properties of the as-printed patterns. In this study, the p-type doping of graphene with CuCl2 as the dopant is realized through liquid phase reaction, and the doped graphene powders are used to prepare the graphene-based conductive inks with a conductivity of 3.13 × 104 S m−1. Subsequently, to simplify the preparation of inks, CuCl2 is directly added into the graphene-based conductive inks, achieving the p-type doped graphene ink with the conductivity of 3.64 × 104 S m−1. The read range of ultrahigh-frequency radio frequency identification antenna and the temperature of the flexible electrothermal film printed with the CuCl2-doped graphene-based conductive inks can reach 7.15 m and 200°C, respectively when the equivalent isotropically radiated power is equal to 4 W and the input power density is 0.94 W cm−2. Moreover, good rheological properties of the conductive inks and high mechanical properties of the printed patterns are also obtained.

A flexible carbon fibre-based electrothermal film for fast actuation of shape memory alloy sheets

Two-dimensional shape memory alloy (SMA) structures have great potential in intelligent and highly flexible robots. However, they have challenges in direct electric heating. This paper proposes a solution to heat SMA sheets using carbon fibres as surface heat sources and indirectly transmits Joule heat generated by the carbon fibres to the SMA sheets. The preparation process of the carbon fibre-based thermoelectric composite film is illustrated in this study. The effect of heat source (carbon fibre) distribution on heat transfer characteristics and the temperature field of the SMA surface is simulated. Then, a functional prototype integrated thermoelectric film and flexible SMA is fabricated, and its effectiveness is verified by local and global activation, respectively. The results show that the composite structure can recover deformation rapidly in 2 s with only 0.7 A running current (applied to each carbon fibre). In addition, the local temperature control method can also realize distributed (spatial dimension) and sequential (temporal dimension) control of the structure. The proposed solution is expected to expand further the design and control of complex, intelligent structures with the development of 4D printing technology.

Variation in Anti-icing Power of Superhydrophobic Electrothermal Film under Different Temperatures and Wind Speeds

Anti-icing with low-energy consumption has important research value for unmanned aerial vehicles. In this study, a superhydrophobic electrothermal film for anti-icing applications was designed and prepared, and power consumption experiments were conducted at different temperatures and wind speeds in an icing wind tunnel. The anti-icing power consumption of the superhydrophobic electrothermal film was lower than that of a traditional electrothermal film. As the temperature decreased or the wind speed increased, the anti-icing power consumption of the two types of electrothermal films increased. A heat flux model was used to analyse the experimental results. It can be concluded that the water collection rate per unit area W and wetting coefficient ξ w are the main factors affecting the power consumption of the superhydrophobic electrothermal film. When the temperature decreased and the wind speed increased, the contact time and contact area between the droplet and the surface affected W and ξ w . Thus, this study is of considerable significance for the design of superhydrophobic electrothermal films for novel anti-icing applications in the future.

Large-Scale Production of Electrothermal Films with GNSs/CNTs/CB Three-Dimensional Structure Ink by Screen Printing

Large-Scale Production of Electrothermal Films with GNSs/CNTs/CB Three-Dimensional Structure Ink by Screen Printing

Glass fiber reinforced graphite/carbon black@PES composite films for high-temperature electric heaters

Carbon based conductive polymer composites as electrothermal materials offers many merits in high flexibility, light weight, low cost, excellent processability, and rapid heating ability, however, the maximum working temperature is usually lower than 200 °C, hampering seriously the medium–high temperature applications. Herein, a series of rationally designed glass fiber reinforced graphite/carbon black@polyethersulfone (G/CB@PES) composites are developed to significantly promote the maximum working temperature over 300 °C. To be specific, the introduced glass fibers acted as rigid skeleton greatly enhance the mechanical strength of PES polymer matrix, thereby offering robust structural stability in high temperature working scenario. Meanwhile, glass fibers not only endow G/CB@PES composite with excellent flame-retardant ability, but also provide rapid thermal conduction channels to reduce the risk of heat accumulation and overheating. More importantly, glass fiber reinforced G/CB@PES composites as electrothermal film heaters exhibit superior electric heating performance in terms of fast temperature responsiveness, high electric heating efficiency, stable maximum working temperatures, and high electric power efficiency under the relatively low applied voltages of 3–21 V. This work provides new insights on the innovative design and facile fabrication of high working temperature electrothermal film heaters in emerging applications.

Flexible, stretchable, waterproof (IPX7) electro-thermal films based on graphite nanoplatelets & polyurethane nanocomposites for wearable heaters

Electrothermal materials have been widely used due to controllable heat energy in our life. With the development of wearable technology, a flexible, safe and waterproof heater with the good ability to endure repeated bending is required in future. In this paper, we have developed a novel wearable heater based on flexible, stretchable graphite nanoplates and polyurethane (GNP/PU) nanocomposite films. Firstly, the GNP/PU thin films with a thickness of 30–200 μm were fabricated in mass production by the method of gap-coating, which can be bent 180° repeatedly, or even knotted for their excellent flexibility, and has a maximum elongation up to 387.8%, due to the homogenous distribution of GNP in PU matrix. By the control on the amount of GNP and the thickness of the film, the minimum resistivity and square resistance of the GNP/PU films can be 80 mΩ·cm and 4 Ω/□, respectively. Through a further flexible structure designing and waterproof electronic packaging process, the fabricated wearable heaters are able to withstand 100,000 180-degrees bending with the resistance changes of only 3.24%, and have a IPX7 waterproof ability to work continuously for 120 min under 1.30 m water. Interestingly, as-prepared bare GNP/PU films have a good resistence to water and salt erosion, with the light 2.1%, 2.4% and 3.1% increasing in electrical resistance, and without obvious change in heating performance, even after the immersion in pure water, 0.5% and 5% salt water and dried completely. Furthermore, the wearable heaters can generate heat uniformly under the safe voltage of 5–24 V to achieve rapid heating and cooling rate of 25 °C/min and 13 °C/min, respectively. Lastly, a heating full-body vest mode of as-prepared wearable heaters was fabricated, which can work well with hand raising, bending and walking. The results showed that as-prepared wearable heaters were very suitable for wearable electronics, due to the excellent flexibility and stretchability of GNP/PU films and their special packaging structure, which provides a new choice for wearable heating products.

Ultraviolet light crosslinked graphene/multi-walled carbon nanotube hybrid films for highly robust, efficient and flexible electrothermal heaters

Based on the Joule heat effect, graphene can transfer electrical into heat energy with fast response times and high efficiencies. Despite intensive researches, facile strategies for preparing polymer-based graphene electrothermal materials remain highly desirable. We herein report a strategy for preparing poly (tetra fluoroethylene) (PTFE)-supported high-performance hybrid electrothermal films from liquid-phase exfoliated graphene by combining with multi-walled carbon nanotubes (MWCNTs). The graphene and MWCNT dispersions can be obtained by sonicating graphite and MWCNTs, respectively, in chloroform with an ultraviolet (UV) light reactive dendritic polymer, HBPE@Py@Acryl, as stabilizer. Further, a series of PTFE-supported, UV cross-linked graphene/MWCNT hybrid films were successfully prepared from the dispersions by vacuum filtration and UV irradiation. It is found that the existence of MWCNTs in the films results in porous structure, making the hybrid films denser than the single graphene system. Meanwhile, the MWCNTs can effectively bridge graphene nanosheets to form perfect hybrid networks, jointly imparting the films with significantly enhanced electrothermal performance. In addition, the UV crosslinking of the HBPE@Py@Acryl adsorbed on the graphene and MWCNT surfaces makes the films exhibit excellent service stability. As an example, after being alternately folded 1800 times or scraped for 90 cycles, the film with 20% MWCNTs remains exhibiting stable, well controllable electrothermal performance. This research provides a guideline for producing high-performance polymer-based graphene electrothermal materials, potentially useful in wearable devices and intelligent actuators, from liquid-phase exfoliated graphene through simple process.

Multiwalled carbon nanotube/cationic cellulose nanofibril electrothermal films: mechanical, electrical, electrothermal, and cycling performances

Multiwalled carbon nanotube/cationic cellulose nanofibril electrothermal films: mechanical, electrical, electrothermal, and cycling performances

A Low-Cost and High-Efficiency Electrothermal Composite Film Composed of Hybrid Conductivity Fillers and Polymer Blends Matrix for High-Performance Plate Heater

Owing to easy processability, ultralight weight, and low cost, carbon- and polymer-based composite materials are among emerging and promising electrothermal materials for high-performance flexible electric heaters. In this work, a sandwich-like structured electrothermal film composed of hybrid conductive fillers [Super-P (SP) and graphite], polymer blends matrix [thermoplastic polyurethane (TPU) and polyethersulfone (PES)], and alumina oxide (Al2O3) as a non-conductive filler has been fabricated by a facile slurry coating method. Hybrid conductive fillers of graphite and SP particles have a uniform spatial distribution in a TPU/PES polymer matrix, which construct a highly stable and continuous conductive network with a low percolation threshold of conductive filler content (14.8 wt.%) that allows electrothermal films to operate at a low applied dc voltage. As for the electrothermal film with 15 wt.% hybrid conductive fillers (SP/G-15 sample), it exhibits a superior response feature, high electrothermal conversion efficiency, stable structural stability and remarkable electrothermal reproducibility. More impressively, SP/G-15 composite electrothermal film as an integrated electric heater for heating water demonstrates a high potential in practical application scenarios.

Rule-Based Control of Battery External Heating for Electric Vehicle During Driving at Low Temperatures

As the only power source of pure electric vehicles, lithium-ion batteries play an important role in vehicle powertrain systems. However, lithium-ion batteries have a significant reduction in capacity and power capability at low temperatures, which results in a greatly shortened driving range and poor acceleration of the vehicle. In this study, a rule-based battery external heating control strategy was developed to heat the battery during driving. The electrothermal film was affixed to the surface of each cell as an external heating material and powered by the battery. An equivalent circuit model combined with a thermal model was established to simulate the electrical and thermal dynamics of the system with sufficiently high accuracy and the control rules were developed based on the model. The optimal solution was obtained by adopting the dynamic programming algorithm to optimize the trade-off between temperature rise and energy consumption and maximize the total driving range under different conditions. Hardware-in-the-loop simulation results show that the vehicle with the proposed control algorithm can increase the total driving range by 18.6% to 220% for different driving conditions at cold to extremely cold temperatures compared with the vehicle without external heating. Furthermore, the rule-based control also shows a 1.1% to 4.4% improvement compared with the maximum (constant) power heating method.