The technology or passive cooling is currently gaining a lot of interest, particularly in the field of modern eco-oriented architecture. It is also possible to combine principles of passive and radiative cooling, which provides an opportunity to achieve practically significant temperature reduction during daytime: a part of heat is avoided by reflecting sunlight, and another portion of heat is thermally radiated to space.
The main obstacle limiting expansion of this passive daytime radiative cooling (PDRC) technology is associated with two issues: such kind of cooling equipment needs expensive and difficult-to-fabricate materials, the performance of which also degrades over time due to surface contamination.
In a research paper recently published on arXiv.org, scientists present a new paper-based material capable of reflecting sunlight and also strongly radiating accumulated heat. A particularly interesting part is that this material also has excellent self-cleaning capabilities: it uses superhydrophobic ethanolic polytetrafluoroethylene (PTFE) coating that protects the paper from moisture and dust contamination. Material is suitable for the outdoor use.
This self-cleaning compound effectively extends the lifespan of the proposed self-cooling material:
We demonstrate a self-cleaning and self-cooling paper made of cellulose fiber-based paper and PTFE particles that can be scalable-fabricated and easily recycled for the PDRC applications. The cooling paper is super “white” in the solar wavelengths, resulting from the backscatter of sunlight by the randomized structure of the cellulose microfibers and PTFE microparticles, while it is infrared “black” in the atmospheric window because of the molecular vibrations of chemical bonds in cellulose and PTFE. The super “white” and “black” features at different wavelengths ensure that the cooling paper has a net radiative cooling loss to the cold outer space. Its performance is better than or on par with other radiative cooling performances as listed in Supplementary Table 2. The outdoor experiment demonstrates the excellent cooling effect in both white and colored forms of the cooling paper. Moreover, the cooling papers possess a self-cleaning and robust surface, which is a benefit to keeping its good cooling performance for the outdoor environment without labor-intensive maintenance. This multifunctional cooling paper provides a promising pathway for practical application in energy-saving and sustainable buildings.
Link to the research paper: https://arxiv.org/abs/2008.11889