Structurally Colored Photonic Janus Films for Switchable Radiative Cooling and Solar Heating

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Personal thermal management (PTM) systems often lack adaptability and tunable optical properties.
• Existing PTM solutions are typically limited to single-mode (cooling or heating) operation.

Purpose of the Study:

• To develop a dual-mode material for PTM with switchable cooling and heating capabilities.
• To integrate tunable optical appearance with thermal regulation in a single platform.

Main Methods:

• Fabrication of a Janus film using cellulose nanocrystal (CNC) photonic structures for cooling and a carbon nanotube (CNT) layer for heating.
• Utilizing pitch modulation in CNC structures for tunable structural color and mid-infrared emissivity.
• Employing CNTs for high solar absorptivity and incorporating Joule heating.

Main Results:

• The film demonstrates switchable radiative cooling (high mid-infrared emissivity up to 0.91) and efficient solar heating (~92% absorptivity).
• Tunable structural color was achieved on the cooling side without compromising performance.
• Reversible switching between cooling and heating modes was accomplished by flipping the film.

Conclusions:

• The developed photonic Janus film offers a viable solution for wearable microclimate control.
• This dual-mode system integrates optical tunability with switchable thermal regulation for adaptive PTM.
• The material's compatibility with continuous fabrication enables scalable production.