Thermochromic Display Research Articles

Brilliant thermochromic photonic liquid dominated by electrostatic repulsion

It is challenging for traditional methods to generate liquid photonic crystals (LPCs) with brilliant colors and clear self-assembly mechanisms, owing to the major limitations in solvent choice and undesired components. Here, novel LPCs with widely tunable solvents and desired components have been successfully fabricated by non-close-assembling silica particles from silica/ethanol solution into target solvents through alternative centrifugation and sonication. The as-fabricated LPCs exhibit 1) brilliant structural colors from high reflectance (maximal: 91 %) by using solvents with low refractive indexes, much higher than those (20–40 %) of traditional LPCs; 2) tunable color saturation with high precision, difficult for conventional LPCs; and 3) a clearer working mechanism: electrostatic repulsion rather than other interactions majorly dominating the non-close-packing of silica particles in solvents. Additionally, a new type of sensitive thermochromic display unit with thermo-switchable on-off structural colors has been prepared by constructing silica/bi-solvents LPCs. This work not only paves a new way for achieving thermal-responsive LPCs but also offers a new perspective for understanding colloidal assembly.

H2 O-Etchant-Promoted Synthesis of High-Quality Graphene on Glass and Its Application in See-Through Thermochromic Displays.

Direct growth of graphene on glass can bring an innovative revolution by coupling the complementary properties of traditional glass and modern graphene (such as transparency and conductivity), offering brand new daily-life related applications. However, preparation of high-quality graphene on nonmetallic glass is still challenging. Herein, the direct route of low sheet resistance graphene on glass is reported by using in situ-introduced water as a mild etchant and methane as a carbon precursor via chemical vapor deposition. The derived graphene features with large domain sizes and few amorphous carbon impurities. Intriguingly, the sheet resistance of graphene on glass is dramatically lowered down to ≈1170 Ω sq-1 at the optical transmittance ≈93%, ≈20% of that derived without the water etchant. Based on the highly conductive and optical transparent graphene on glass, a see-through thermochromic display is thus fabricated with transparent graphene glass as a heater. This work can motivate further investigations of the direct synthesis of high-quality graphene on functional glass and its versatile applications in transparent electronic devices or displays.

Improving the optical transparency of film heaters based on silver nanowire/polyimide composite films

A highly transparent and flexible thin film heater based on silver nanowires (AgNWs) was fabricated by a facile full-solution method. Here, we firstly embedded AgNWs in colorless polyimide (cPI) to ensure thermal stability and flexibility of transparent film heater, and then deposited an antireflective (AR) layer of silica (SiO2) on AgNW/cPI film to improve the transmittance of the composite film. The developed highly transparent film heater exhibits an increase of 3.5% in transmittance at 550 nm at a sheet resistance of 17.0 Ω sq−1 for SiO2/cPI/AgNW composite film. At the same time, the film heater shows an excellent heating performance and mechanical flexibility. Furthermore, the application of the composite film in thermochromic display devices was also demonstrated. Such encouraging results show large potential for thermochromic display devices and other heating systems.

Highly Stretchable and Wearable Thermotherapy Pad with Micropatterned Thermochromic Display Based on Ag Nanowire–Single‐Walled Carbon Nanotube Composite

AbstractDue to the increasing interest in wearable devices, flexible and stretchable film heaters have been widely studied, as alternatives to heaters with conventional rigid shapes. Herein, a highly stretchable film heater (SFH) based on the silver nanowire (Ag NW)–single‐walled carbon nanotube composite with a thermochromic display on a polydimethylsiloxane (PDMS) substrate is successfully fabricated. The SFH shows excellent electrical conductivity, high mechanical stretchability, and outstanding reliability, with no significant degradation after 10 000 stretching cycles under tensile strain. The SFH can be heated to the target temperature (≈60 °C) within 30 s at a low applied voltage. In addition, a thermochromic display is fabricated to help prevent the risk of low‐temperature burns. Red (R), green (G), and blue (B) thermochromic microparticles (TMPs) are synthesized using drop‐based microfluidic technology. The TMPs show RGB colors at room temperature but change to a white color above a certain temperature. The TMPs are arrayed into a PDMS stencil on the basis of their particle sizes using the rubbing technique. The micropatterned thermochromic display, which functions as a visual alarm, combined with the SFH can pave the way for the development of thermotherapy pads for next‐generation wearable devices in the medical field.

High‐Sensitivity, Skin‐Attachable, and Stretchable Array of Thermo‐Responsive Suspended Gate Field‐Effect Transistors with Thermochromic Display

AbstractThe fabrication of a skin‐attachable, stretchable array of high‐sensitivity temperature sensors is demonstrated. The temperature sensor consists of a single‐walled carbon nanotube field‐effect transistor with a suspended gate electrode of poly(N‐isopropylacrylamide) (PNIPAM)‐coated gold grid/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate and thermochromic leuco dye. The sensor exhibits a very high sensitivity of 6.5% °C−1 at temperatures between 25 and 45 °C. With increasing temperature, the suspended gate electrode bends due to the deswelling of the PNIPAM, resulting in the reduction of the air gap to increase the drain current under a constant gate voltage. At the same time, the leuco dye coated on top of the transparent gate electrode changes color to visualize changes in temperature. The 4 × 6 integrated temperature sensor array integrated using liquid metal interconnections exhibits mechanical and electrical stability under 50% biaxial stretching and allows for the spatial mapping of temperature with visual color display regardless of wrist movement while attached to the skin of the wrist. This work is expected to be widely useful in the development of skin‐attachable electronics for medical and health‐care monitoring.

Printed thermochromic displays

Thermochromic displays, which were evaluated in this study, combine printed electronics with the thermochromism phenomenon. Conductive lines printed on the reverse side and thermochromic printing ink printed on the front side of cardboard packaging form a thermochromic display that gives cardboard packaging additional value. Displays were printed on different printing materials, and thermochromic printing ink was deposited in one and two layers. In addition, half of the samples were varnished. The influence of the printing material, the thickness of the thermochromic printing ink layer, the varnish, the high temperature, and light fastness on the display's operability were all evaluated. It was clearly shown that the choice of printing material plays a crucial role in the display's operability. Moreover, high temperature and light fastness also have a significant influence, although the impact is negligible when the display is used at room temperature.

Thermal conductive and flexible silastic composite based on a hierarchical framework of aligned carbon fibers-carbon nanotubes

One-dimensional carbon structures are ideal fillers for improving the thermal conductivity (κ) of flexible carbon/polymer composites. However, the aligned pathways usually result in anisotropic heat conduction. Here, a three-dimensional (3D) hierarchical framework is fabricated by electrostatic flocking, using aligned carbon fibers and vertically aligned carbon nanotubes (CF-VACNTs). Theoretical simulations show that the VACNTs anchoring on the CFs improves the heat conduction of the composite in both the axial and the radial directions of the CFs, by absorbing and transferring heat from silastic (SI) matrix to CFs. The thermal conductivity in the through-thickness (κ⊥) and in-plane (κ∥) directions of aligned carbon fiber-carbon nanotube/silastic (ACF-VACNT/SI) composite could be improved by optimizing the CF transfixion structure and the VACNT network, through the length and rank of VACNTs and the alignment of CF-VACNTs. ACF-VACNT/SI with 60 μm in length and crisscross quadruple VACNT rows exhibits both a high κ⊥ (7.51 W mK−1) and a high κ∥ (3.72 W mK−1), suggesting good heat transfer in both two directions even under compression and bending. A thermochromic display device based on ACF-VACNT/SI confirms that the composite is suitable for application as thermal interface materials in wearable intelligent electronic devices.

Spatiotemporally controllable acoustothermal heating and its application to disposable thermochromic displays

Disposable thermochromic displays using spatiotemporally controllable acoustothermal heating are reported. A variety of thermochromic displays are presented to prove the applicability of the proposed thermochromic display system.

Load characteristics of a suspended carbon nanotube film heater and the fabrication of a fast-response thermochromic display prototype.

The influence of heating load on the thermal response of a CNT film heater has been studied. Two kinds of heat dissipation modes, thermal radiation in a vacuum and convection in the atmosphere, are investigated, respectively. It is found that the thermal response slows down with the load quantities in the both cases. We have further studied the thermal response of a CNT film loaded with thermochromic pigment, which is a kind of phase change material. In addition to the thermal response slowing down with the load quantity, it is also found that the phase change of the thermochromic pigments can also slow down the thermal response. With a suspended CNT film heater structure, we have fabricated a thermochromic display prototype, which can switch from room temperature to 50 °C in about 1 s with a brightness contrast of 4.8 under normal indoor illumination. A 16 × 16 pixel thermochromic display prototype can dynamically display Chinese characters driven by a homemade circuit.

Flexible Reflective Color Displays using Thermochromic Pigments

This research presents a flexible reflective thermochromic display (TCD) comprised of thermochromic pigments and a patterned indium tin oxide (ITO) film coated on a polyethylene naphthalate (PEN) substrate, and the display's thermo-optical characteristics. The display showed maximum red, green, and blue reflectances of 30%, 38%, and 29%, respectively. Furthermore, the display exhibited a continuous grey color when the temperature was changed continuously. As a flexible display, the display showed reliable thermo-optical performance without image damage even when highly bent. We expect the proposed TCD will be used in outdoor information display applications where low cost is a key factor.

Reflective Thermochromic Display on Polyethylene Naphthalate Film

A reflective flexible display was fabricated by placing a thermochromic pigment on a polyethylene naphthalate (PEN) substrate coated with an indium tin oxide (ITO) film, and its thermo-optical characteristics were investigated. The reflective thermochromic display showed good image quality with a reflectance of approximately 65%. As a flexible display, the display showed reliability without damage to the image even after the display was bent strongly. The reflective display cell exhibits continuously the gray level according to the temperature controlled by applied voltage. This low cost display is expected be used in outdoor poster applications where information needs to be presented clearly.

A Reflective Display Based on Thermochromic Pigment

This research presents thermally activated monochromatic reflective display produced by very simple method based on thermochromic pigment and its thermo-optical properties are investigated. The display exhibits maximum white reflectance of about 48%. The bright level of this thermochromic display (TCD) cell is continuously tuned by the temperature changes under adjusting the driving voltage to the TCD cell. It also showed a wide viewing angle above 80° without any optical components. This display is considerable for applications where indoor or outdoor poster information must be presented clearly with low cost.

Reflective color display using thermochromic pigments

A reflective thermochromic display fabricated by a very simple method using three kinds of thermochromic pigments is produced and its thermo-optical characteristics are investigated. The display exhibits maximum red, green, and blue reflectances of 38%, 30%, and 35%, respectively. The reflective display cell shows continuous gray color with changing temperature, which is crucial for multicolor displays. It also shows an excellent viewing angle above 80° without any of the additional optical components that are required in liquid crystal displays. We expect that this display technology will be used for outdoor billboard information display applications.