KAIST Professor Song Young-min’s research team has developed a nature-inspired heat management technology that adapts to environmental changes by mimicking the heat regulation strategies of poplar leaves, which reflect sunlight by curling and exposing their undersides during hot and dry conditions and prevent frost damage by releasing heat at night through moisture on their surfaces. The team, in collaboration with Professor Kim Dae-hyung’s team from Seoul National University, has created a flexible hydrogel-based thermal regulator (LRT) that autonomously transitions between cooling and heating modes. This technology manages latent heat through water evaporation and condensation, and radiative heat using light reflection and transmission, all within a single device. The key material combines lithium ions (Li⁺) and hydroxypropyl cellulose (HPC) in a PAAm hydrogel structure. Li⁺ absorbs and condenses surrounding moisture to adjust latent heat and maintain warmth, while HPC changes between transparent and opaque based on temperature, regulating solar reflection and absorption to switch between cooling and heating.
The LRT, crafted by the research team, autonomously adjusts heat via four mechanisms: absorbing and condensing atmospheric moisture to release heat and maintain warmth in dew-point conditions; transmitting sunlight and using absorbed near-infrared radiation for heating on cold days with weak sunlight; facilitating strong evaporative cooling by releasing internal moisture in hot and dry environments; and reflecting sunlight through opaqueness induced by HPC at high temperatures and strong sunlight, thereby enhancing natural cooling through evaporative mechanisms. Without requiring power, this biomimetic thermal management device self-adjusts to its surroundings by switching between cooling and heating modes.
In outdoor experiments, the LRT maintained temperatures up to 3.7°C cooler in summer and up to 3.5°C warmer in winter compared to existing cooling materials. Simulations in seven climate zones (according to ASHRAE standards) demonstrated an annual energy savings potential of up to 153 MJ/m² over traditional roof coatings. This research exemplifies the engineering implementation of sophisticated natural heat management functions and is expected to be utilized in scenarios where power-based heating and cooling are challenging, such as building exteriors, roofs, temporary shelters in disaster zones, and outdoor storage facilities.
Professor Song Young-min remarked, “This research is significant as it presents a heat management device that self-adapts to season and climate changes by engineering nature’s intelligent heat regulation strategies. It holds the potential to be expanded into an intelligent thermal management platform applicable in various environments.”