Soft Coating Cools Wearable Devices

Scientists at the City University of Hong Kong have developed a coating for wearable technologies that can help to dissipate heat, reducing the chances of skin burns and increasing the life of such devices. Electronic devices can generate heat, but this can be problematic for wearables that are in constant contact with the skin. The heat may be uncomfortable, may overheat the device itself, and could even cause skin burns. The flexible coating designed by these researchers enables both radiative and non-radiative cooling and does not require electronic power to function. The coating is less than 1 millimeter thick and consists of hollow silicon dioxide (SiO2) microspheres that enhance infrared radiation, and titanium dioxide (TiO2) nanoparticles and fluorescent pigments that enhance solar reflection. In tests so far, the coating has reduced the temperature of an electronic resistor from 140.5°C to 84.2°C, demonstrating an impressive 56°C drop (103 F).

Wearable technologies have enormous potential in the medical field, providing unobtrusive monitoring of a variety of health parameters. However, these electronic devices can produce heat, and when the device is in constant contact with the skin this can cause problems. The electrical components within the device can generate heat and the device can also become heated by external factors, such as the sun and warm air. Overheating can damage sensitive devices and disrupt their measurements, and in certain cases wearables could even cause skin burns if the temperature exceeds a safe threshold.

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“Skin-like electronics are an emerging development in wearable devices,” said Yu Xinge, one of the chief designers of the new coating. “Effective thermal dissipation is crucial for maintaining sensing stability and a good user experience. Our ultrathin, soft, radiative-cooling interface, made of dedicatedly designed photonic material, provides a revolutionary solution to enable comfortable, long-term healthcare monitoring, and virtual and augmented reality (VR/AR) applications.”

Researchers have developed coatings that are designed to reduce the heat coming from wearable technologies, but in some cases these have been bulky and rigid, thereby interfering with the functionality of the device. Moreover, most approaches have relied on non-radiative methods (conduction and convection) to dissipate the heat, and do not take advantage of radiative means in the form of thermal radiation emitted from the surface of the wearable.

This latest coating allows both radiative and non-radiative heat dissipation. It consists of titanium dioxide (TiO2) nanoparticles and fluorescent pigments that can enhance solar reflection along with silicon dioxide (SiO2) microspheres that enhance infrared radiation. In tests so far, the coating has demonstrated impressive cooling abilities, helping to reduce the surface temperature of an electronic resistor from 140.5°C to 84.2°C, leading to a striking 56°C drop with a coating thickness of just 600 μm.

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