The work titled
“Self-stratified stretchable passive cooling interface for thermal management of on-skin electronics” was published in
Soft Science on May 25, 2026.
Skin-interfaced electronics are becoming increasingly capable of continuously monitoring health, supporting human–machine interaction, and processing multiple types of physiological information. However, placing increasingly complex electronics directly on the skin creates an important thermal-management challenge. Electrical operation generates internal heat through Joule heating, while solar irradiation and high ambient temperatures impose additional external thermal loads. Excessive temperature may reduce wearing comfort, raise safety concerns, and distort physiological signals during long-term monitoring.
Existing cooling strategies often address only one of these heat sources. Conventional heat sinks and active cooling components can be bulky, rigid, or energy-consuming, making them unsuitable for soft and stretchable devices. Radiative-cooling coatings can reduce solar heating, but they generally do little to spread and dissipate heat generated by the electronic components themselves. A multidisciplinary research team from Sun Yat-sen University, City University of Hong Kong, and The Hong Kong Polytechnic University has developed a self-stratified stretchable passive cooling interface, or SPCI, that addresses both internal and external thermal loads within a single soft encapsulation material.
The SPCI is prepared by mixing aluminum oxide particles and liquid-metal droplets into a silicone elastomer, followed by spin coating and controlled curing. During curing, the density differences among the components drive their spontaneous redistribution: the denser liquid-metal droplets preferentially sediment toward the bottom, while aluminum oxide particles become enriched in the upper region, with a gradual transition forming between them. Because sedimentation and elastomer crosslinking occur simultaneously, the functional layered architecture is formed through a one-step self-stratification process, without the need to separately fabricate and bond multiple cooling layers.
The aluminum-oxide-rich upper region strongly scatters and reflects incoming sunlight while also emitting thermal radiation. The liquid-metal-rich lower region forms a thermally conductive network close to the electronic circuit, allowing heat generated by the device to spread laterally and dissipate more efficiently. This architecture therefore combines an “external-blocking” function with an “internal-dissipation” function.
Optical and mechanical measurements showed that the material had an average solar reflectance of 92.6% and a mid-infrared emissivity of approximately 90%. The resulting composite reached a thermal conductivity of approximately 1.5 W·m⁻¹·K⁻¹. Despite the addition of these functional materials, the interface remained soft, with an elastic modulus of approximately 0.082 MPa, and could withstand more than 800% tensile strain before breaking.
The SPCI reduced the maximum temperature of stretchable serpentine circuits by up to 8.4 °C indoors and approximately 12 °C during outdoor testing under solar exposure. Its cooling performance was maintained under tensile deformation, indicating that the liquid-metal heat-spreading network remained effective as the device stretched. When integrated into a wireless skin-interfaced photoplethysmography platform, the SPCI lowered the maximum device temperature by 8.6 °C during continuous outdoor operation. This thermal regulation also improved physiological signal acquisition: the recorded pulse waves showed clearer periodicity, more stable amplitudes, and better preservation of fine waveform features, including the dicrotic notch. Fine pulse-wave features remained identifiable after exercise, even in the presence of sweating and motion disturbance.
The density-driven, one-step self-stratification process is compatible with scalable fabrication methods such as spin coating and can be integrated with flexible circuits produced by different manufacturing techniques. By forming the functional layers directly during curing, the approach simplifies fabrication and offers potential for scalable batch production and future large-area manufacturing. The interface may therefore serve as both a cooling layer and a compliant encapsulation interface for wearable health monitors, smart clothing, human–machine interfaces, and other flexible electronic systems.
The study remains a proof-of-concept demonstration evaluated under a limited range of environmental conditions and in relatively short-term tests. Future work should assess performance across different climates and longer wearing periods, while further addressing long-term liquid-metal leakage resistance, large-area fabrication, and encapsulation uniformity.
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