[Weekly news] Making summer cooler & winter warmer without power

Korea Advanced Institute of Science and Technology (KAIST) announced this week that its research team has developed a power-free, self-regulating thermal management material that keeps surfaces cooler in summer and warmer in winter by mimicking the natural temperature-control strategy of the poplar tree. 

The ivory tower took an example of the poplar, which survives extreme heat and cold by curling its leaves during hot, dry weather to expose reflective surfaces and by releasing latent heat at night through moisture condensation. 

Although such biological strategies are highly sophisticated, recreating them in artificial materials has been a significant challenge. The newly developed material greatly expands the potential of passive thermal regulation for buildings, roofs, and temporary shelters.

The KAIST team headed by Prof. Song Young-min created a flexible hydrogel-based device called the Latent-Radiative Thermostat (LRT) in collaboration with Prof. Kim Dae-hyeong’s group at Seoul National University. 

This bio-inspired material autonomously alternates between heating and cooling depending on temperature, humidity, and sunlight, and integrates two natural regulatory processes within a single structure, according to KAIST.

The LRT uses a composite material in which lithium ions (Li⁺) and hydroxypropyl cellulose (HPC) are embedded within a polyacrylamide hydrogel. 

The Li⁺ component absorbs and condenses moisture to generate warming through latent heat release, while the HPC transitions between transparent and opaque states in response to temperature. 

When temperatures rise, the HPC molecules aggregate and turn the material opaque, reflecting solar radiation to enhance cooling. 

When conditions are cold, the transparent state allows sunlight to pass through, while absorbed moisture contributes to heating by capturing near-infrared radiation. 

Depending on environmental conditionsm, the LRT naturally switches among modes that either retain heat or release it through evaporative cooling, operating entirely without electricity, KAIST noted. 

“This research is significant as it technically reproduced nature's intelligent thermal regulation strategy, presenting a thermal management device that self-adapts to seasonal and climate changes," Prof. Song said.

"It can be expanded into an intelligent thermal management platform applicable to various environments in the future.” 

The research was published online early this year in Advanced Materials, a world-leading journal in the field of material science.