Superhydrophilic cooling and superhydrophobic heating honeycomb Janus foam for all-weather thermal management in complex environments

Abstract

Zero-energy and environmentally favorable passive radiative cooling and heating (PRC/PRH) materials do not function satisfactorily under atmospheric back-radiation (cloudy, humid, reduced clarity) or for all-season building thermal management requirements. A biphasic honeycomb Janus foam (CF/HF) that exhibits superhydrophilic properties for cooling and superhydrophobic characteristics for heating is proposed to achieve superior radiative thermal management under various weather conditions. CF/HF exhibits an exceptionally rapid wicking time of 0.233 s, which facilitates straightforward, expedient, and efficient rehydration of the system. Concurrently, the honeycomb configuration of CF/HF enables efficient solar reflection (∼91%), and the intrinsic molecular oscillation within the PAAS + PDMS polymer chains aids in the dispersal of emitted heat through the atmospheric window (∼96.1%). Due to the combined cooling action, it is possible to attain a temperature reduction of 5.6 °C even under overcast conditions with an average solar irradiance of 410.7 W/m². Furthermore, exceptional capabilities in both solar and electrothermal (joule) heating of the HF/CF foam serve as a potent supplementary strategy for the thermal management of buildings amidst unpredictable weather scenarios, especially in the extreme weather of icing, which is crucial for preserving the structural integrity of buildings and alleviating energy demands, among other benefits.