Sanghyun Ju

In this study, a pixelated full‐color display based on a near‐infrared (NIR) laser‐driven thermochromic liquid crystal (TLC) was developed. TLCs exhibit temperature‐dependent colors through Bragg reflection induced by variations in the helical pitch of their cholesteric structure. However, a Gaussian temperature distribution originating from the heating center causes color nonuniformity within the activated region (rainbow effect), while lateral heat diffusion to adjacent regions limits the realization of pixelated displays. To address these challenges, a pixelated multilayer structure (TLC/Graphite/Al/PDMS/Glass) was fabricated by integrating a graphite layer for NIR photothermal conversion with an Al thin film serving as an in‐plane heat spreader. The pixel size and spacing were optimized to achieve RGB color separation, visual color distinguishability, and thermal isolation. As a result, red (∼27°C), green (∼29°C), and blue (∼31°C) colors were clearly generated without mutual interference, enabling the reproduction of complex full‐color images. The proposed TLC‐based photothermally driven display enables full‐color image generation via non‐contact optical actuation, eliminating the need for electrical wiring and demonstrating potential for next‐generation form‐factor display applications, including smart windows, anti‐counterfeiting tags, and wearable devices.

A design for a light-irradiation-based color-conversion display that uses carbon nanotubes (CNTs) to achieve efficient photothermal conversion and heat dissipation.

As modern electronic devices become smaller and more highly integrated, stable thermal management is emerging as a key development approach, including in applications considering mechanical deformation. In this study, a flexible heat-dissipating sheet was developed using composites of insulating graphene (I-Gr), plate-like boron nitride (BN-P), and aggregated spherical BN (BN-A) based on a high-elasticity styrene–(ethylene–butylene)–styrene (SEBS) elastomer. The unique asymmetric two-dimensional layered structure of I-Gr and BN improved the heat transfer properties of the composite by maintaining the continuity of the heat-conducting network despite tensile deformation. In addition, the spherical shape and disordered structure of the aggregated BN-A promoted the formation of an extended heat-conducting path and enhanced the bonding between the fillers. At the optimal composition, the composite maintained an initial thermal conductivity (TC) of 2.0 W m⁻¹ K⁻¹ or higher, and the TC reduction (ΔTC) was less than 8% and 10% at 50% and 100% elongation, respectively, demonstrating excellent TC stability. In addition, owing to the interfacial affinity and network reinforcing effect of I-Gr, the TC performance and structural stability were maintained even after 500 cycles of 50% tensile strain and 400% elongation. In contrast, the CNT-based composite showed limitations such as low initial TC, large ΔTC, and low elongation. This study presents a design strategy for a heat-dissipating material with high elasticity, high TC, and excellent durability, offering considerable potential for use in next-generation flexible electronic devices such as wearable electronics, freeform displays, and soft robotics.

This study analyzes a reusable, washable air filter with a nanoNet structure fabricated by methods such as plasma treatment and low-temp heat fusion. The filter's durability is tested through repeated washing cycles.

This paper presents a polychromatic display (PD) utilizing thermochromic liquid crystals (TLCs) that exhibit temperature-dependent color changes operated via near-infrared (NIR) laser scanning. TLCs in the cholesteric phase can produce red, green, and blue colors by adjusting their layer spacing and pitch in response to the thermal expansion induced by temperature changes. A simplified TLC-based PD (TLC-PD) panel was constructed by combining a TLC thin film with an NIR absorption and heat-generating functional film, eliminating the need for complex electronic circuits. By inducing a photothermal reaction through NIR laser irradiation, this configuration allows straightforward and precise color image formation without conventional display mechanisms. In addition, the precise control of the red, green, and blue color intensities was achieved by adjusting the NIR laser power, with the display exhibiting response and decay times of ∼4.7 and 5.3 s, respectively. The developed low-power TLC-PD can present full-color text and images in real time through laser scanning, making it applicable in various energy-efficient display technologies.

In this paper, we introduce an innovative approach for generating robotic faces with a thermal signature similar to that of humans and equipping prosthetic or robotic hands with a lifelike temperature distribution. This approach enhances their detection via infrared cameras and promotes more natural interactions between humans and robots. This method integrates a temperature regulation system into artificial skin, drawing inspiration from the human body’s natural temperature control via blood flow. Central to this technique is a fiber network simulating blood vessels within the artificial skin. Water flows through these fibers under specific temperature and flow conditions, forming a controlled heat release system. The heat emission can be adjusted by changing the dilation of these fibers, primarily by modulating the frequency of circulation. Our findings indicate that this approach can replicate the varied thermal characteristics of different human faces and hand areas. Consequently, the robotic faces appear more human-like in infrared images, aiding their identification by infrared cameras. At the same time, the prosthetic hands achieve a more natural temperature, reducing the discomfort typically felt in direct contact with synthetic limbs. The aim of this study was to address the challenges faced by the users of prosthetic hands. The results from this study show a promising direction in humanoid robotics, fostering improved tactile interactions and redefining human–robot relationships. This innovative technique facilitates further advancements, blurring the lines between artificial aids and natural biological systems.

We report on developing a wearable infrared (IR) display based on stretchable conductive fibers fabricated through an expansion–contraction process. The expansion process creates a gap between the strands of spandex fibers. This is achieved by immersing the fibers in a solvent where carbon nanotubes (CNTs) are dispersed, thereby embedding the CNTs. Contraction is achieved through a drying process, which removes the gap between the strands of the spandex fibers. This ensures that the CNTs remain embedded, even after repeated stretching. The CNT-embedded spandex fibers are arranged into a 5 × 7 pixel array. The intensity of the IR rays emitted from the fibers can be controlled by adjusting their temperature, which is achieved by varying the driving voltage. Full-color IR images and displays of letters and numbers are realized through precise control of the IR light intensity. The wearable IR display developed in this study opens up exciting possibilities for integration into advanced systems such as military identification, artificial intelligence robots, autonomous driving, and aerospace industry applications.

The sensor, designed to be worn directly on the skin, is suitable for real-time monitoring of the recovery level of not only general wounds, but also difficult-to-heal wounds, such as those with chronic inflammation. Notably, healthy skin has a pH range of 4–6. When a wound occurs, the pH is known to be approximately 7.4. In this study, alpha-naphtholphthalein (Naph) was immersed in a cotton-blended textile to produce a wearable halochromic sensor that clearly changed color depending on the pH of the skin in the range 6–9, including pH 7.4, which is the skin infection state. The coating was performed without using an organic solvent by dissolving it in micelle form using cetyltrimethylammonium bromide, a surfactant, in water. Naph-based halochromic sensor shows light yellow, which is the dye’s own color, at pH 6, which is a healthy skin condition, and gradually showed a clear color change to light green-green-blue as pH increased. Even after washing and drying by rubbing with regular tap water, the color change due to pH was maintained more than 10 times. Naph-based halochromic sensors use a simple solution production and coating method and are not only reusable sensors that can be washed with water but also use environmentally friendly water, making them very suitable for developing commercial products for wound pH monitoring. In addition, it can be easily applied to medical supplies, such as medical gauze, patient clothes, and compression bandages, as well as everyday wear, such as clothing, gloves, and socks. Therefore, it is expected to be widely used as a wound pH sensor, allowing real-time monitoring of the skin condition of individuals with chronic skin inflammation, including patients requiring wound recovery.

Studies have attempted to improve thermal conductivity by complexing polymers. Via the complexing of photothermal materials with a heat-sensitive polymer, heat can be generated internally, thus resulting in efficient changes in the properties of the heat-sensitive polymer. This study fabricated an optical writing display to locally induce heat generation in poly(N-isopropylacrylamide) (pNIPAM), which is a heat-responsive material, using the photothermal effect of a near-infrared (NIR) absorbing material. Cesium tungsten oxide (CTO), an NIR-absorbing material, exhibits excellent properties due to its photothermal properties. By mixing carbon nanotubes (CNTs), the photothermal effect caused by NIR rays was strengthened and was more effectively controlled by providing thermal conductivity characteristics. The CNT–CTO hybrid absorbed the NIR laser, converted it into heat, and transmitted it to the adjacent pNIPAM network. When pNIPAM received heat, a hydrophilic–hydrophobic phase transition occurred, and a white pattern was observed owing to a change in the refractive index inside the hydrogel. Upon stopping the application of the NIR laser, rapid cooling occurred due to the high thermal conductivity of the CNTs, and the hydrophobic–hydrophilic phase transition was quickly achieved and restored. Therefore, based on the results of this study, optical writing displays using heat-responsive polymers containing photothermal particles and NIR lasers are expected to be applicable for information transmission in extreme environments, such as aviation, space, and the military, owing to the ability of lasers to travel in a straight line.

Cesium tungsten oxide with strong near-infrared radiation absorbance and carbon nanotubes with high thermal conductivity were optimally combined within hydroxypropyl cellulose to implement the thermoresponsive display.