A domestic research team has developed an artificial material that mimics the thermal management strategy of poplar leaves. It is expected to be used as a thermal management technology that autonomously regulates temperature without power for building exteriors, roofs, and temporary shelters.
A team led by Song Young-min, a professor in the School of Electrical Engineering at the Korea Advanced Institute of Science and Technology (KAIST), said on the 18th that it developed a "flexible hydrogel-based thermal regulator (LRT)" that mimics poplar's natural heat-regulation mechanism, together with Seoul National University Professor Kim Dae-hyung. The study was published online on the 4th (local time) in the international journal Advanced Materials.
Poplars have a survival strategy of rolling their leaves to expose the underside and reflect sunlight when it is hot and dry, and at night preventing cold damage with heat (latent heat) released by moisture forming on the leaf surface. However, there have been few cases of implementing such a sophisticated thermal management system in artificial materials.
Mimicking this, the researchers developed a thermal regulator that autonomously switches between cooling and heating. It is a new thermal management technology that can simultaneously implement latent-heat control through evaporation and condensation of moisture and radiative-heat control using light reflection and transmission in a single device.
The core material is a structure that combines lithium ions and hydroxypropyl cellulose (HPC) in a hydrogel. Lithium ions absorb and condense ambient moisture to regulate latent heat and maintain warmth, while HPC becomes transparent or opaque depending on temperature changes and adjusts solar reflection and absorption to switch between cooling and heating modes.
When the temperature rises, HPC molecules aggregate, making the hydrogel opaque, which reflects sunlight and enhances natural cooling. The resulting flexible hydrogel-based thermal regulator automatically switches among four thermal control modes depending on ambient temperature, humidity, and illuminance.
On cold nights or in environments below the dew point, it absorbs and condenses moisture in the air, releasing heat to stay warm; on cold days with weak sunlight, it transmits sunlight and the absorbed moisture takes in near-infrared light to produce a heating effect. In hot and dry environments, internal moisture evaporates to produce strong evaporative cooling, and under strong sun and high temperatures, HPC becomes opaque to reflect sunlight while evaporative cooling simultaneously operates to lower the temperature.
In outdoor experiments, the flexible hydrogel-based thermal regulator maintained temperatures up to 3.7 degrees lower in summer and up to 3.5 degrees higher in winter than conventional cooling materials. In simulations across seven climate zones, it showed an annual energy-saving effect of up to 153 MJ/㎡ compared with existing roof coatings.
Professor Song Young-min said, "This research is meaningful as a technology that engineeringly reproduces nature's intelligent thermal regulation strategy and presents a thermal management device that autonomously adapts to seasonal and climate changes," adding, "It could be expanded into an intelligent thermal management platform applicable to various environments."
References
Advanced Materials (2025), DOI: https://doi.org/10.1002/adma.202516537