A zero-energy dual-mode thermoregulator: A robust Janus film for switchable radiative cooling and solar heating

Abstract

This study introduces a Janus composite film designed for dual-mode thermal management to address global energy needs and climate challenges through a combination of passive daytime radiative cooling and solar heating. The film incorporates aramid nanofibers to enhance the processing of a polyether ether ketone (PEEK) matrix. It also strategically arranges mica, hexagonal boron nitride, graphene nanoplatelets, and multi-walled carbon nanotubes to create a bi-modal packing network. The resulting composite film demonstrates remarkable bidirectional thermal regulation, achieving a sub-ambient radiative cooling of 7.24 °C and an above-ambient solar heating of 10.46 °C, alongside anisotropic in-plane thermal conductivity of 3.58 W m⁻¹ K⁻¹. Theoretical calculations indicate significant radiative powers: 59.44 W m⁻² for daytime cooling, 107.82 W m⁻² for nighttime cooling, and 496.97 W m⁻² for daytime heating. Meanwhile, EnergyPlus simulations reveal considerable potential for energy savings in building applications. By harmonizing opposing thermal regulation mechanisms within a single PEEK-based composite, this research advances the design of multifunctional materials for climate-responsive technologies, providing a practical solution to reduce fossil fuel dependence while maintaining thermal comfort in various operational scenarios. The outstanding thermal stability and weather resistance of PEEK matrices also present a potential for composite materials to be applied in extreme environments such as aerospace.