Rationally Tuning Phase Separation in Polymeric Membranes toward Optimized All-day Passive Radiative Coolers

Abstract

The all-day passive radiative cooler has emerged as one of the state-of-the-art energy-saving cooling tool kits but routinely suffers from limited processability, high cost, and complicated fabrication processes, which impede large-scale applications. To address these challenges, this work exploits a polymer-based passive radiative cooler with optimized turbidity, reconfigurability, and recyclability. These cooling membranes are fabricated via selective condensation of octyl side chain-modified polyvinyl alcohol through a non-solvent-induced phase separation method. The rational tuning over spatial organization and distribution of the air–polymer interface renders optimized bright whiteness with solar reflectance at 96%. Meanwhile, the abundant −C–O–C– bonds endow such membranes with infrared thermal emittance over 90%. The optimized membrane realizes a subambient cooling of ∼5.7 °C with an average cooling power of ∼81 W m–2 under a solar intensity of ∼528 W m–2. Furthermore, the supramolecule nature of the developed passive radiative cooling membrane bears enhanced shape malleability and recyclability, substantially enhancing its conformability to the complex geometry and extending its life for an eco-friendly society.

Biomimetic Robust All‐Polymer Porous Coatings for Passive Daytime Radiative Cooling

“…Interestingly, different from the isotropic cellular structures of many PDRC materials reported before, [ 5,16,18,19,30,47,48 ] the network structure of the coating exhibits an anisotropic laminated morphology, in which the skeleton filaments have a Cyphochilus beetle‐like orientation perpendicular to thickness direction (Figure 1c,d; Figure S7a,b, Supporting Information). [ 38,42 ] The size of pores in cross‐section is about half that of the pores viewed from the surface while skeletons have a uniform size (Figure S7f,g, Supporting Information).…”

“…In contrast, in a traditional NIPS process based on a physical phase separation mechanism, the polymer solution systems could remain in the metastable state long enough for the nucleation growth phase separation process to occur, forming an isotropic cellular-like structure after the vitrification of the polymer-rich skeleton. [5,30,41,47,48] Based on the optical properties of the Cyphochilus beetle structure, the orientation of the scatterers along the direction perpendicular to the incident light can produce more efficient light scattering and provide stronger reflection performance for the visible light. [38,42] Moreover, the filling fraction of the coating is 64 ± 1% (i.e., the porosity of 36 ± 1%), which approaches the upper limit of the scatterer volume fraction range (40-70%) for the optimal broad-band visible reflectance in the beetle-like anisotropic structures.…”

MOF-Integrated Hierarchical Composite Fiber for Efficient Daytime Radiative Cooling and Antibacterial Protective Textiles

“…The most common one is the active cooling technology based on the vapor compression system; however, it consumes a large amount of power and needs complicated equipment, which is not appropriate for outdoor and personal applications. , Other technologies, including the use of phase change materials, semiconductor-cooling textiles, air-cooling textiles, , and liquid-cooling textiles, are not mature enough as personal cooling equipment due to limitations of weight, volume, and cost. Passive daytime radiative cooling (PDRC), as a zero-power cooling technology, offers another promising approach for personal thermal management (PTM), through rationally regulating the immediate microclimate around the human body that provides thermal comfort. − Recently, state-of-the-art PTM textiles have been developed, such as nanofiber membranes, − nanoporous membranes, − microfiber fabrics, , and coating fabrics, − and demonstrated excellent cooling ability through strongly shielding against incident solar radiation and dissipating heat energy via mid-infrared (MIR) emission through the atmosphere’s longwave infrared (LWIR) transparency window to the ultra-cold outer space. − …”

Flexible Radiative Cooling Textiles Based on Composite Nanoporous Fibers for Personal Thermal Management

“…Previous researchers have carried out abundant studies in this field and provided a great deal of possible cases. These efforts mainly focus on the effects of different polymers, − porous and hollow fibers, − morphological control of fibers, − and nanoparticle-doped fibers − on the spectrum and cooling performance of fabrics. There are still many defects in the existing studies, while certain cooling effects can be achieved.…”

“…30 Although the method has not yet been utilized to create porous fiber fabrics, it is demonstrated to be feasible to porous adjustability in nonfiber polymer films. 12 In this work, a high-efficiency radiative cooling textile was prepared from PLA porous fibers by means of electrostatic spinning and steam-induced phase separation. By governing the relative humidity of air in the electrostatic spinning box, the porosity and pore size can be adjusted.…”