Three-Dimensional Printable Nanoporous Polymer Matrix Composites for Daytime Radiative Cooling

Abstract

Daytime radiative cooling presents an exciting new strategy for combating global warming, because it can passively cool buildings by reflecting sunlight and utilizing the infrared atmospheric window to eject heat into outer space. Recent progress with novel material designs showed promising subambient cooling performance under direct sunlight. However, large-scale implementation of radiative cooling technologies is still limited by the high-cost and complex fabrication. Here, we develop a nanoporous polymer matrix composite (PMC) to enable rapid production and cost reduction using commercially available polymer processing techniques, such as molding, extrusion, and 3D printing. With a high solar reflectance of 96.2% and infrared emissivity > 90%, the nanoporous PMC achieved a subambient temperature drop of 6.1 °C and cooling power of 85 W/m 2 under direct sunlight, which are comparable to the state-of-the-art. This work offers great promise to make radiative cooling technologies more viable for saving energy and reducing emissions in building cooling applications.

PolyChemPrint: A hardware and software framework for benchtop additive manufacturing of functional polymeric materials

“…27 The nanoporous SiO 2 -PE-oil feedstock was prepared by mixing SiO 2 particles (< 10 μm, Sigma-Aldrich), highdensity polyethylene pellets (Sigma Aldrich), ultrahigh molecular weight PE powder (Alfa Aesar) and paraffin oil (light, Fisher Chemical) as reported elsewhere. 30 PS-b-PLA bottlebrush block copolymer films for laser annealing were prepared by spin-coating 100 μl of 128 mg/ml solution in Toluene (Sigma Aldrich) onto plasma-treated Corning glass substrates. The best film uniformity was achieved following a 3-step procedure: for 30s, first accelerating at 100 rpm/s to hold at 1000 rpm, then for 15 s accelerating @1200 rpm/s to hold at 3000 s, and finally spinning down to 0 rpm @1200 rpm/s.…”

“…The high-pressure extrusion configuration (SI 3.2.2, Figure 5(A), Figure S6) is suitable for extruding high viscosity and thermoplastic materials and is a variation of a design previously reported by White et al 29 Here, the tool head is a pressure-multiplying attachment (hp3cc from Nordson EFD) with gas supply from the same Ultimus V dispenser as in the low-pressure case. To provide stable 30 Copyright (2020) American Chemical Society heating, we use a cylindrical resistive heater fitted to the extruder, with machined spacers with external insulation. The temperature is set and maintained by a closed-loop controller (Watlow EZ-Zone) connected to the barrel with an embedded thermocouple probe.…”

Colorful surfaces for radiative cooling

“…However, due to strong scattering and diffraction within solar spectral range, most radiative cooling materials are white in color. [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] For a colored radiative cooling structure, absorption in the visible range is inevitable. Therefore, one needs to consider the balance between solar heating and thermal radiation for colored radiative cooling materials.…”

Accurately Quantifying Clear-Sky Radiative Cooling Potentials: A Temperature Correction to the Transmittance-Based Approximation

“…Models that yield the level of detail needed for such calculations are comparatively rare [1,5,13]. One model, which has achieved almost universal use in recent radiative cooling literature, is the transmittance-based cosine approximation [1,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], which was first used as part of a more comprehensive model by Granqvist in 1981 [1]. This model assumes that the irradiance of the atmosphere originates from greenhouse gases, including water vapor, carbon dioxide and ozone, and calculates the spectral, angular sky irradiance based on an effective spectral angular emittance as follows:…”

“…Since the irradiance from ozone and absorptance/emittance of SiO films have little overlap and the SiO film has a narrowband emittance, such a choice is justifiable in that context. However, the approximation has since been used to calculate the radiative cooling potentials of ideal emitters and cooling powers of radiative coolers with different spectral emittances, leading to both a systematic underestimation of cooling potential and a related overestimation of performance [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The MODTRAN hemispherical emittance, which is more accurate, should ideally be used instead.…”