Aerogel‐Functionalized Thermoplastic Polyurethane as Waterproof, Breathable Freestanding Films and Coatings for Passive Daytime Radiative Cooling

Abstract

Passive daytime radiative cooling (PDRC) is an emerging sustainable technology that can spontaneously radiate heat to outer space through an atmospheric transparency window to achieve self-cooling. PDRC has attracted considerable attention and shows great potential for personal thermal management (PTM). However, PDRC polymers are limited to polyethylene, polyvinylidene fluoride, and their derivatives. In this study, a series of polymer films based on thermoplastic polyurethane (TPU) and their composite films with silica aerogels (aerogel-functionalized TPU (AFTPU)) are prepared using a simple and scalable non-solvent-phase-separation strategy. The TPU and AFTPU films are freestanding, mechanically strong, show high solar reflection up to 94%, and emit strongly in the atmospheric transparency window, thereby achieving subambient cooling of 10.0 and 7.7 °C on a hot summer day for the TPU and AFTPU film (10 wt%), respectively. The AFTPU films can be used as waterproof and moisture permeable coatings for traditional textiles, such as cotton, polyester, and nylon, and the highest temperature drop of 17.6 °C is achieved with respect to pristine nylon fabric, in which both the cooling performance and waterproof properties are highly desirable for the PTM applications. This study opens up a promising route for designing common polymers for highly efficient PDRC.

Dual-Mode Porous Polymeric Films with Coral-like Hierarchical Structure for All-Day Radiative Cooling and Heating

“…Radiative thermal management, particularly for passive radiative cooling (PRC) and passive radiative heating (PRH) without additional energy input, has drawn increasing attention in academia and industries as an alternative for traditional energy-intensive cooling/heating approaches. − PRC uses cold outer space (∼3 K) as the ultimate heat sink for the earth through the transparent atmospheric window (i.e., 8–13 μm). , For all-day PRC, particularly in the daytime, high emissivity within the atmospheric window and high solar reflection within the solar spectrum (i.e., 0.3–2.5 μm) of materials are synchronously anticipated to realize net cooling power under direct solar irradiation . Various material morphologies (e.g., film, − coating, , textile, and aerogel) and material structures (e.g., multilayer structure, , metamaterial structure, , randomly distributed particle, , and porous structure , ) have been developed to realize efficient all-day PRC. Meanwhile, PRH is realized by reducing radiative heat loss through the reflection of infrared thermal radiation emitted by an object with a temperature exceeding absolute zero. − Therefore, low infrared emissivity in materials, such as metals and surface metalized polymeric films, , is required for efficient PRH.…”

Bioinspired Multilayer Structures for Energy-Free Passive Heating and Thermal Regulation in Cold Environments

“…However, in recent years, the emerging passive radiative cooling − only effectively provides cooling in hot conditions. It fails to adapt to applications in extremely cold regions such as high latitudes, the Arctic and Antarctic regions, or in winter when the ambient temperature is low.…”

Polyurethane-Coated Polyaniline/SiO2 Nanoparticle Electrospun Nanofiber Membranes for Waterproof and Moisture-Permeable Materials

“…PAN and PU are both commonly used polymers for preparing electrospinning nanofibers for their advantages of solution spinnability, fiber morphology, and membrane mechanical properties and porosity. , SiO 2 is nontoxic and environmentally friendly and has good stability. It also has the characteristics of not absorbing sunlight and having high reflection to sunlight and can be used for the radiative cooling field. − In this study, PAN/SiO 2 was used as the shell, PU was used as the core, and the PAN/SiO 2 –PU composite nanofiber membrane was prepared by coaxial electrospinning. The effects of the feeding rate ratio of the shell–core solution and the SiO 2 content in the shell solution on the structure, mechanical properties, and waterproofness and moisture permeability of composite fiber membranes were studied.…”