Self-sorting coating cuts circuit temperatures by up to 21.6°F in tests

At Sun Yat-sen University, a wireless heart-rate monitor was tested under direct sunlight with a stretchable cooling interface added to its surface. The coating lowered the device’s surface temperature by 15.5°F compared with a standard elastomer-encapsulated version, without drawing extra power. Led by Jiyu Li and Zehua Peng, the team published the results in Soft Science.

The material begins as one liquid mixture containing aluminum oxide microparticles and liquid metal suspended in a stretchable elastomer. As it cures, the fillers separate by density into two layers. The aluminum oxide-rich layer rises to the top and reflects 92.6 percent of incoming sunlight; the liquid-metal-rich layer sits below it and conducts heat at around 1.5 watts per meter-kelvin, moving heat away from the electronics.

On a serpentine circuit running at 200 milliwatts, the coating cut peak temperatures by up to 15.1°F indoors and 21.6°F outdoors in direct sunlight. It stretched beyond 800 percent of its original length while retaining a soft, skin-compatible feel. The researchers also reported stable performance after 1,000 stretching cycles and 100 heating-cooling cycles.

The payoff was visible in the monitor’s data. The device used photoplethysmography, or PPG, a technique for tracking blood flow through the skin. The cooled version preserved key pulse-wave features with more than 95 percent accuracy, versus roughly 30 percent for the uncooled control, and maintained more than 80 percent accuracy after the wearer exercised. Its signal-to-noise ratio reached 19 decibels, compared with 6 decibels for the control.

So what changes in practice? A passive coating could help skin-worn health monitors and other flexible electronics keep collecting cleaner signals during prolonged outdoor use, while avoiding a separate power demand for cooling. The researchers describe the material as a scalable option for smart clothing and wearable devices.