Spectral selective textile for passive radiant outdoor personal cooling

Abstract

The invention relates to a spectrally selective textile for passive radiation outdoor personal cooling. A textile comprising: (1) a substrate; and (2) a particulate filler dispersed in the matrix. The textile has a transmittance of infrared radiation at a wavelength of 9.5 [mu] m of at least about 40% and a weighted average reflectance of radiation in a wavelength range of 0.3 [mu] m to 2 [mu] m of the textile is at least about 40%.

Description

[0001] This application is a divisional application of a patent application for invention titled "Spectral Selective Textiles for Passive Radiative Outdoor Personal Cooling", with the application number 201980011257.8, the filing date of February 4, 2019, and which entered the Chinese national phase on July 31, 2020.

[0002] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 62 / 626,532, filed on February 5, 2018, the entire content of which is incorporated herein by reference.

[0003] Statement Regarding Federally Sponsored Research or Development This invention was made with government support under Contract No. DE - AR0000533 awarded by the Department of Energy. The government has certain rights in this invention. BACKGROUND OF THE INVENTION

[0004] Outdoor heat stress poses a serious threat to public health and restricts industrial labor supply and productivity, thus having an adverse impact on the health and economy of society. However, there is a lack of an effective and economical method that can provide local outdoor human cooling without being restricted by humidity and wind levels.

[0005] In this context, it is necessary to develop the embodiments of the present disclosure.

[0006] Overview In some embodiments, a textile includes: (1) a matrix; and (2) particulate fillers dispersed in the matrix. The transmittance of the textile for infrared radiation at a wavelength of 9.5 μm is at least about 40%, and the weighted average reflectance of the radiation of the textile in the wavelength range from 0.3 μm to 2 μm is at least about 40%.

[0007] In some embodiments of the textile, the matrix includes at least one polyolefin.

[0008] In some embodiments of the textile, the matrix includes at least one of polyethylene or polypropylene.

[0009] In some embodiments of the textile, the peak particle size of the particulate fillers is in the range of about 10 nm to about 4000 nm.

[0010] In some embodiments of the textile, the particulate fillers include inorganic materials.

[0011] In some embodiments of the textile, the particulate fillers include at least one of metal oxides, metal halides, or metal sulfides.

[0012] In some embodiments of the textile, the particulate filler comprises at least one of zinc oxide, potassium bromide, cesium iodide, potassium chloride, sodium chloride, or zinc sulfide.

[0013] In some embodiments of the textile, the difference in refractive index between the particulate filler and the matrix is at least about ±5% relative to the refractive index of the matrix.

[0014] In some embodiments of the textile, the transmittance of infrared radiation at a wavelength of 9.5 μm is at least about 60%.

[0015] In some embodiments of the textile, the weighted average reflectance of radiation in the wavelength range from 0.3 μm to 2 μm is at least about 60%.

[0016] In some embodiments of the textile, the matrix is porous.

[0017] In some embodiments of the textile, the volume percentage of pores within the matrix is at least about 5%.

[0018] In some embodiments of the textile, the peak pore size of the pores within the matrix is in the range of about 10 nm to about 4000 nm.

[0019] In some embodiments of the textile, the textile comprises a fiber that comprises a matrix and particulate filler dispersed within the matrix.

[0020] In some embodiments of the textile, the textile comprises a film that comprises a matrix and particulate filler dispersed within the matrix.

[0021] In additional embodiments, the textile comprises: (1) a matrix; (2) particulate filler dispersed within the matrix. The transmittance of infrared radiation of the textile at a wavelength of 9.5 μm is at least about 40%, and the textile has a peak reflectance at wavelengths within the visible range corresponding to a specific color.

[0022] In some embodiments of the textile, the particulate filler comprises at least one of a metalloid, a metal oxide, or a metal cyanide.

[0023] In additional embodiments, a method of regulating body temperature comprises placing the textile of any of the foregoing embodiments near a human body.

[0024] In a further embodiment, a method of forming a porous textile comprises: (1) forming a mixture of a solvent, at least one polymer, and particulate filler, wherein the particulate filler comprises an inorganic material having a transmittance of infrared radiation at a wavelength of 9.5 μm of at least about 40%, and the particulate filler has a peak particle size in the range of 10 nm to 4000 nm; (2) extruding the mixture to form a textile comprising the solvent and the particulate filler dispersed within the textile; and (3) extracting the solvent from the textile to form a porous textile.

[0025] In some embodiments of the method, the at least one polymer comprises a polyolefin.

[0026] In some embodiments of the method, the particulate filler comprises at least one of zinc oxide, potassium bromide, cesium iodide, potassium chloride, sodium chloride, or zinc sulfide.

[0027] Other aspects and embodiments of the present disclosure are also contemplated. The foregoing summary and the following detailed description are not intended to limit the present disclosure to any particular embodiment, but are merely intended to describe some embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To better understand the nature and objects of some embodiments of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

[0029] FIG. 1(a). Schematic diagram of a porous film of some embodiments.

[0030] FIG. 1(b). Schematic diagram of a non-porous film of some embodiments.

[0031] Figure 2 . Schematic diagrams of (a) a woven textile, (b) a porous polymer fiber, and (c) a non-porous polymer fiber of some embodiments.

[0032] Figure 3 . (a) Schematic diagram illustrating the paths of heat input and output of a human body in sunlight in an outdoor environment. (b) Schematic diagram of a nanoporous polyethylene (PE) textile embedded with zinc oxide (ZnO) nanoparticles, which is designed for radiative outdoor cooling by reflecting sunlight and transmitting human body heat radiation. (c) Spectral comparison of AM 1.5G sunlight radiation and human body heat radiation simulated using Planck's law at a skin temperature of approximately 34°C, showing marginal overlap in the wavelength range.

[0033] Figure 4. (a) Simulation of the normalized scattering cross-section of individual ZnO particles with particle diameters varying from 0.01 to 10 μm in the wavelength range of 0.4–16 μm in a polyethylene medium. (b) Comparison of the normalized scattering cross-section between ZnO particles with the same diameter of 320 nm and air pores in a polyethylene medium. Dependence of (c) solar reflectance and (d) mid-infrared transmittance of multiple ZnO particles embedded in nanoporous polyethylene on the size and density of ZnO particles. For each data point in (c) and (d), the scattering cross-section is averaged with a normal distribution of particle sizes with a variance of ±0.1 μm. Solar reflectance is averaged over the solar irradiance spectrum range of 0.4 to 4 μm. Mid-infrared transmittance is averaged over the human body thermal radiation wavelength range of 4 to 16 μm. (e) Projection of the three-dimensional plots in (c) and (d) onto the density-versus-size plane. The white region presents the optimal density and size of ZnO particles where high solar reflectance and high mid-infrared transmittance can be achieved.

[0034] Figure 5 . (a) Image of the ZnO-PE textile under sunlight. (b) Side and top views of the X-ray computed tomography image of the ZnO-PE sample, showing that the ZnO particles are generally uniformly distributed. The inset is a distribution plot of the ZnO particle diameters measured using dynamic light scattering, which peaks at approximately 500 nm. (c) Image of a roll of ZnO-PE fibers made by melt-extrusion. Scanning electron microscope (SEM) images show the (d) upper surface and (e) cross-section of the ZnO-PE thin film sample. (f) High-magnification SEM image showing the morphology of individual ZnO particles. (g) Reflectance and transmittance spectra of ZnO-PE in the ultraviolet to mid-infrared range (approximately 0.3 to approximately 16 μm) measured by integrating spheres. The shaded regions show the AM 1.5G solar spectrum (left) and the human body radiation spectrum (right) for reference.

[0035] Figure 6. (a) Image of the thermal measurement device in an outdoor test environment. (b) Schematic diagram of the thermal measurement device, which includes a heater simulating the skin, a thermocouple measuring the temperature of the simulated skin, and a textile sample covering the simulated skin. (c) On a sunny spring day in Stanford, California, over a period of about four hours, compare the temperatures measured by the ZnO-PE-covered, cotton-covered, and bare simulated skin heaters under wind convection. Measure the ambient temperature and solar irradiance and plot them for reference. (d) Based on the measurements in (c), calculate the additional cooling power requirements for the ZnO-PE-covered, cotton-covered, and bare simulated skin heaters to maintain a normal skin temperature of about 34 °C. (e) Compare the temperatures measured by the ZnO-PE-covered, cotton-covered, and bare simulated skin heaters under wind convection and sweat evaporation. (f) Compare the cooling power requirements of the ZnO-PE-covered, cotton-covered, and bare simulated skin heaters at 13:00 in (d) and the cooling power provided by sweat evaporation, where the cooling power is estimated as the product of the water evaporation rate through the textile ( Figure 12 ) and the latent heat of vaporization of water.

[0036] Figure 7 . Ultraviolet-visible-near-infrared (UV-VIS-NIR) reflectance and Fourier transform infrared (FTIR) emissivity of human skin.

[0037] Figure 8 . UV-VIS-NIR reflectance and FTIR transmittance of cotton.

[0038] Figure 9 . Comparison of measured (solid lines) and simulated (dashed lines) reflectance and transmittance spectra of ZnO-PE in the ultraviolet to mid-infrared range (0.3 - 16 μm). The following parameters are assumed for the simulation to closely match the experimental values: average air pore diameter of 200 nm, porosity of 20%, ZnO:PE mass ratio of 2:5, normal distribution of ZnO particle diameter of d = 0.5 μm ± 0.1 μm, and film thickness of 150 μm. The shaded areas show the AM 1.5G solar spectrum (left) and the human radiation spectrum (right) for reference.

[0039] Figure 10 . Measure the skin temperature of the simulated skin heater without textile coverage in sunlight and shadow.

[0040] Figure 11 . Schematic diagram of the heat transfer model of a clothed human body in sunlight.

[0041] Figure 12 . Compare the skin temperatures calculated from the heat transfer model analysis with the measured values of cotton- and ZnO-PE-covered skin.

[0042] Figure 13 The water evaporation rates of ZnO-PE-covered skin, cotton-covered skin, and bare skin.

[0043] Figure 14 The effects of ZnO-PE layer thickness on (a) solar light reflection and (b) mid-infrared transmission. As the thickness of the nanocomposite layer increases, a trade-off is observed, where a thickness of approximately 80 μm to approximately 160 μm is optimal for both high solar light reflection and mid-infrared transmission.

[0044] Figure 15 Inductively coupled plasma mass spectrometry (ICP-MS) measurements to quantify Zn in water before and after washing the ZnO-PE textile material with detergent and stirring for approximately 30 minutes 2+ Concentration. The results show that during washing, trace amounts of ZnO (approximately 2 parts per billion (ppb)) were released into the water. Due to the tight encapsulation of PE on the ZnO particles, the good durability of the embedded structure was demonstrated.

[0045] Figure 16 The 1 1H nuclear magnetic resonance (NMR) spectrum (top figure) of the textile sample dissolved in chloroform-d to detect residual dichloromethane in the sample. The bottom curve is from chloroform-d (the solvent used for 1 1H NMR measurements) as a blank control. The peak at approximately 7.26 ppm corresponds to chloroform-d. The water peak at approximately 1.56 ppm is due to the absorption of trace amounts of moisture from the atmosphere. The peak position of dichloromethane should be at approximately 5.3 ppm, which is absent in the sample curve. These measurements confirm that dichloromethane is very volatile and can be removed substantially completely by evaporation. After drying in air for approximately 2 hours, no residual dichloromethane was detected from the textile sample.

[0046] Figure 17 Black is achieved by adding micron-sized silicon particles to polyethylene, which also shows high infrared transparency in the wavelength range of approximately 4 to approximately 18 μm. (a) shows the black Si-PE composite film. (b) shows the black Si-PE fiber together with other colored polyethylene fibers. (c) Infrared transmission spectrum of the Si-PE composite film.

[0047] Figure 18.(a) Schematic design of the coloring of radiative cooling textiles, which is achieved by mixing IR-transparent inorganic pigment nanoparticles with PE. The mixed composite can then be extruded into continuous fibers to be woven into an intertwined textile through a large-scale industrial process. (b) Photograph and (c) FTIR absorption spectrum of the selected inorganic pigment powder. (d) SEM images of nanoparticles of Prussian blue (PB), (e) iron oxide (Fe2O3), and (f) silicon (Si).

[0048] Figure 19 .(a) Photograph, (b) UV-VIS reflectance, (c) FTIR transmittance, and (d) visible opacity spectrum of a polyethylene composite film mixed with pigment nanoparticles.

[0049] Figure 20 .(a) Photograph of three colored polyethylene fiber spools produced by industrial extrusion. (b) Tensile strength tests show that the colored polyethylene fibers have a tensile strength comparable to that of cotton. (c) Optical micrographs of extruded fibers of blue PB-PE, (d) red Fe2O3-PE, and (e) yellow Si-PE. (f–h) Optical micrographs show the weaving pattern, and (i–k) photographs of woven textiles with good abrasion resistance.

[0050] Figure 21 .(a) Measuring the total FTIR transmittance of colored polyethylene textiles. (b) Graph showing the negligible (ppb level) increase in the concentration of various metal ions in water after washing the colored polyethylene textiles. (c) Comparing the temperatures measured by a bare and a textile-covered skin mock heater. Textile samples include cotton, PB-PE, Fe2O3-PE, Si-PE, and nanoporous polyethylene (nanoPE). (d) Infrared images of bare skin and human skin covered with cotton, PB-PE, Fe2O3-PE, and Si-PE textiles.

[0051] Description Embodiments of the present disclosure are directed to spectrally selective textiles. In some embodiments, a polymer textile that is sunlight-reflective, infrared (IR)-transparent, and embedded with particles is provided for outdoor wearers, which achieves cooling performance in a direct sunlight in an outdoor environment to maintain thermal comfort.

[0052] Heat exchange between the human body and the outdoor environment involves conduction, convection, evaporation, and radiation. Therefore, maintaining outdoor thermal comfort involves reducing heat stress by reducing heat gain and increasing heat loss. Other methods mainly focus on the evaporative and convective heat losses of clothing to achieve outdoor cooling, but both of these heat dissipation paths have their own constraints, which largely depend on environmental conditions such as humidity and wind level. Although solar irradiance and the radiative heat transfer path contribute significantly to the overall heat exchange, they have not been fully considered for outdoor textiles. Different from ordinary textiles, IR-transparent textiles reflect a high percentage of sunlight and have a low absorption rate of IR absorbed by the human body, thus reducing the input of radiative heat transfer and increasing the output of radiative heat transfer without additional energy consumption, making the wearer feel cooler in the outdoor environment. Additionally, polymer composites can be formed into fibers by extrusion, and woven textiles can be formed from the fibers by weaving, thus providing the comfort and breathability of textiles close to the skin. Therefore, this textile is suitable for mass production. Similarly, the embodiments of the present disclosure provide sunlight-reflecting, IR-transparent textiles for outdoor personal cooling, which maintain the comfort of textiles close to the skin and can also be achieved on a large scale.

[0053] Some embodiments of the IR-transparent textiles have a low absorption of IR radiation emitted by the human body, so that the IR radiation can be freely transmitted to the environment and cause the wearer to feel cooler. At the same time, the textile is provided with particulate fillers dispersed within the textile, which are used to scatter the solar irradiance spectrum, thus providing a cooling effect under direct sunlight. Additionally, the textile can be porous, and the pores in the textile can make the textile breathable and increase heat dissipation through conduction and convection. The textile can be formed as a porous film embedded with particulate fillers, or can be formed as a fiber-based woven structure. Polymer fibers with pores and embedded with particulate fillers can be formed on a large scale by methods such as extrusion and solvent extraction, and woven textiles can be formed from such fibers on a large scale by methods such as weaving.

[0054] The textiles of some embodiments include a single polymer or a mixture of two or more different polymers. In some embodiments, to impart IR transparency, polymers or mixtures of polymers with low IR radiation absorption can be used, such as low radiation absorption in the mid-IR range of about 4 μm to about 20 μm or about 4 μm to about 16 μm. In such embodiments, suitable polymers include polyolefins, such as polyethylene (PE), polypropylene (PP), and other thermoplastic polyolefins or polyolefin elastomers. For PE, suitable molecular weight ranges can be low density PE (LDPE), high density PE (HDPE), and ultra-high molecular weight PE (UHMWPE). PE can be mixed with other polymers or at least partially replaced by other polymers, such as PP, polyvinyl chloride (PVC), vinylon, polyacrylonitrile (PAN), polyamides (such as nylon), polyethylene terephthalate (PET), polyesters, polyvinyl fluoride (PVF), copolymers, other thermoplastic polymers, natural polymers, etc. Other polymers that can be used instead of or in combination with polyolefins have low IR radiation absorption, such as polymers that are substantially free of one or more of the following functional groups: C-O, C-N, aromatic C-H, and S=O, and for example, polymers in which the content of one or more of these functional groups is no greater than about 1 mmol / g, no greater than about 0.1 mmol / g, no greater than about 0.01 mmol / g, no greater than about 0.001 mmol / g, or no greater than about 0.0001 mmol / g. In some embodiments, the transmittance of IR radiation at a wavelength of 9.5 μm for suitable polymers is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, up to about 98%, or more. In some embodiments, the weighted average transmittance of IR radiation in the wavelength range of 7-14 μm for suitable polymers is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, or more. During the textile formation process, one or more additives can be included, such as antioxidants, antimicrobial agents, colorants or dyes, water absorbents (such as cotton), metals, wood, silk, wool, etc. One or more additives can be dispersed in the polymer or mixture of polymers included in the textile.

[0055] The textiles of some embodiments further include particulate fillers dispersed in a polymer or a mixture of polymers. The particulate fillers provide a contrast with respect to the refractive index of the polymer or polymer mixture included in the textile to selectively scatter light in a desired spectrum, particularly strongly scatter light in the desired spectrum, but scatter little in the mid-IR range. In some embodiments, the particulate fillers have a certain size and a material composition to selectively scatter light in the solar irradiance spectrum in the range of about 300 nm to about 4 μm, including radiation in the visible light range of about 400 nm to about 700 nm and radiation in the near-IR range of 700 nm to about 4 μm, thereby providing a cooling effect under direct sunlight. In other embodiments, the particulate fillers have a certain size and a material composition to selectively scatter certain wavelengths or colors in the visible range, thereby providing a coloring effect. For example, the particulate fillers (and textiles including such fillers) can have a peak reflectance at a specific wavelength in the visible range corresponding to a specific color (e.g., about 450 nm), thereby producing a visual appearance of that specific color (e.g., blue), or can have a peak reflectance at another specific wavelength in the visible range corresponding to another specific color (e.g., about 600 nm), thereby producing a visual appearance of that other specific color (e.g., yellow), or can have a peak reflectance at another specific wavelength in the visible range corresponding to another specific color (e.g., about 750 nm), thereby producing a visual appearance of that other specific color (e.g., red), and so on.

[0056] In some embodiments, the relative difference in refractive index between the particulate filler and the polymer or polymer mixture included in the textile is at least about ±1%, e.g., at least about ±5%, at least about ±8%, at least about ±10%, at least about ±15%, at least about ±20%, at least about ±25%, at least about ±30%, at least about ±35%, at least about ±40%, at least about ±45%, or at least about ±50% with respect to the refractive index of the polymer or polymer mixture included in the textile (e.g., for visible light measured at 589 nm). In some embodiments, the absolute difference in refractive index between the particulate filler and the polymer or polymer mixture included in the textile is at least about ±0.01, e.g., at least about ±0.05, at least about ±0.1, at least about ±0.15, at least about ±0.2, at least about ±0.25, at least about ±0.3, at least about ±0.35, at least about ±0.4, at least about ±0.45, at least about ±0.5, or at least about ±0.55 with respect to the refractive index of the polymer or polymer mixture included in the textile (e.g., for visible light measured at 589 nm). The refractive index of the particulate filler can be higher or lower than the refractive index of the polymer or polymer mixture included in the textile.

[0057] Examples of suitable materials for the filler include inorganic materials that have low absorption of radiation in the range of about 300 nm to about 20 μm, including radiation in the visible light range, radiation in the near-IR range, and radiation in the mid-IR range. For example, metalloids (such as silicon), metal oxides (such as zinc oxide and iron oxide), metal halides (such as potassium bromide, cesium iodide, potassium chloride, and sodium chloride), metal sulfides (such as zinc sulfide), metal cyanides (such as Prussian blue), and the like. In some embodiments, the transmittance of the suitable material of the filler for IR radiation at a wavelength of 9.5 μm is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, up to about 98%, or more. In some embodiments, the weighted average transmittance of the suitable material of the filler for IR radiation at wavelengths of 7 - 14 μm is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, or more. The size of the filler is set to primarily scatter radiation in the visible light range and the near-IR range rather than radiation in the mid-IR range. For example, the filler can be nanoscale (e.g., as nanoparticles), such that it is comparable to the wavelength of visible light and lower than the wavelength of mid-IR radiation. In some embodiments, the average or peak particle size of the filler is in the range of about 10 nm to about 4000 nm, about 1000 nm to about 4000 nm, about 100 nm to about 1000 nm, about 100 nm to about 900 nm, about 100 nm to about 800 nm, about 100 nm to about 700 nm, about 100 nm to about 600 nm, about 100 to about 500 nm, about 100 nm to about 400 nm, about 100 nm to about 300 nm, about 500 nm and 1000 nm, about 200 nm and 900 nm, about 300 nm and 800 nm, about 400 nm and 700 nm, or about 400 nm and 600 nm, but larger or smaller fillers can also be considered. In some embodiments, the distribution of the particle size can be controlled to impart a desired wavelength of scattered radiation. For example, the size of the filler can be relatively uniform, such that the standard deviation of the particle size is no greater than about 50%, no greater than about 45%, no greater than about 40%, no greater than about 35%, no greater than about 30%, no greater than about 25%, or no greater than about 20% of the average particle size. In some embodiments, the number density of the filler in the textile is at least about 0.1 μm -3 , at least about 0.5 μm -3 , at least about 1 μm -3 , at least about 2 μm -3 , at least about 4 μm -3 , or at least about 6 μm -3 , and up to about 8 μm-3 Or greater. The filler can be of regular or irregular shape and can have an aspect ratio of about 3 or less or greater than about 3.

[0058] The textiles of some embodiments are porous. The size of the pores of the textile can be set to contribute, together with the filler, to the selective scattering of light in a desired spectrum. For example, the pores can be of nanoscale dimensions (e.g., as nanopores), such that they are comparable to the wavelengths of visible light and lower than the wavelengths of mid-IR radiation. In some embodiments, the average or peak pore size is in the range of about 10 nm to about 4000 nm, about 1000 nm to about 4000 nm, about 100 nm to about 1000 nm, about 100 nm to about 900 nm, about 100 nm to about 800 nm, about 100 nm to about 700 nm, about 100 nm to about 600 nm, about 100 to about 500 nm, about 100 nm to about 400 nm, about 100 nm to about 300 nm, about 500 nm and 1000 nm, about 200 nm and 900 nm, about 300 nm and 800 nm, about 400 nm and 700 nm, or about 400 nm and 600 nm, but larger or smaller pores can also be contemplated. In some embodiments, the distribution of the pore size can be controlled to impart a desired wavelength of scattered radiation. For example, the pore size can be relatively uniform, such that the standard deviation of the pore size is no greater than about 50%, no greater than about 45%, no greater than about 40%, no greater than about 35%, no greater than about 30%, no greater than about 25%, or no greater than about 20% of the average pore size. The pore size can be determined using, for example, the Barret-Joyner-Halenda model. In some embodiments, the volume percentage of pores within the textile is at least about 1%, at least about 5%, at least about 10%, at least about 15%, or at least about 20%, and up to about 30% or more. In some embodiments, at least some of the pores can be interconnected to increase breathability and increase conductive and convective heat dissipation through the interconnected pores. The pores can be of regular or irregular shape and can have an aspect ratio of about 3 or less or greater than about 3.

[0059] The textiles of some embodiments can be formed as a porous film 100, which includes a matrix 102 of a polymer or a mixture of polymers having pores 104 and embedded particulate filler 106 (see FIG. 1(a)), or can be formed as a non-porous film 110, which includes a matrix 112 of a polymer or a mixture of polymers and embedded particulate filler 116 (see FIG. 1(b)). The textiles of additional embodiments can be formed as a fiber-based woven textile 200 (see Figure 2(a)). In the case of a woven textile 200, the porous polymer fibers 202 included in the textile 200 include an elongate member 204 having pores 206, and particulate filler 208 dispersed within the elongate member 204. Alternatively or in combination, the non-porous polymer fibers 212 included in the textile 200 include an elongate member 214 without pores, and particulate filler 218 dispersed within the elongate member 214. Generally, the polymer fibers may have a circular cross-sectional shape, as well as various other regular or irregular cross-sectional shapes, such as multi-lobed, octagonal, elliptical, pentagonal, rectangular, square, trapezoidal, triangular, wedge-shaped, and the like. The surface of the fibers may be chemically or physically modified to impart other properties, such as hydrophilicity, antimicrobial properties, coloring, texture, and the like. For example, a coating may be applied to the surface of the fibers to impart hydrophilicity, such as a coating of a hydrophilizing agent. In some embodiments, the polymer fibers include a plurality (e.g., two or more) of elongate members that are joined or otherwise combined to form the entirety of the fiber. At least one of the elongate members includes particulate filler dispersed therein, and the elongate members may include the same polymer (or the same polymer blend) or different polymers (or different polymer blends). The elongate members may be arranged in a variety of configurations. For example, the elongate members may be arranged in a core-sheath configuration, an island-in-sea configuration, a matrix or checkerboard configuration, a segmented-pie configuration, a side-by-side configuration, a striped configuration, and the like. Other embodiments of the polymer fibers may be implemented as having a hollow structure, a block structure, a grafted structure, and the like.

[0060] In some embodiments, textiles are formed by extrusion and solvent extraction methods. In particular, a polymer or a mixture of polymers can be combined with particulate fillers in a solvent such as paraffin oil to form a mixture. The volume percentage of the solvent in the mixture can be selected to obtain a desired volume percentage of pores in the resulting textile after solvent extraction, such as at least about 1%, at least about 5%, at least about 10%, at least about 15%, or at least about 20%, and up to about 30% or more. Instead of paraffin oil or in combination with paraffin oil, other suitable liquid solvents or solids can be used, such as solid waxes, mineral oils, etc. Also, one or more additives can be included in the mixture, such as water absorbents, colorants, etc. The mixture can then be extruded through an extrusion device to form a film or polymer fibers including the solvent dispersed therein, and the solvent is extracted to leave nanopores. The extraction of the solvent can be carried out by immersion in a chemical bath of an extractant (such as dichloromethane), but other extraction methods can be considered, such as evaporation. Once formed, the polymer fibers of some embodiments can undergo various processes to form a woven textile as individual fibers or as included in a multi-fiber yarn. Examples include weaving, knitting, felting, plaiting, braiding, etc. In some embodiments, polymer fibers containing different particulate fillers to produce different colors are combined or mixed in specific proportions to form a woven textile having a desired color.

[0061] Textiles of some embodiments can exhibit a variety of benefits. In some embodiments, the transmittance of the textile to IR radiation at a wavelength of 9.5 μm is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, up to about 98%, or more. In some embodiments, the weighted average transmittance of the textile to IR radiation in the wavelength range of 7 - 14 μm is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, or more. In some embodiments, the weighted average reflectance of the textile to radiation in the wavelength range of 0.3 - 2 μm is at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, or at least about 80%, and up to about 90%, up to about 95%, up to about 98%, or more.

[0062] Textiles of some embodiments can be incorporated into a fabric as a single layer in a single-layer fabric or as multiple layers (e.g., two or more layers) in a multi-layer fabric. In the case of a multi-layer fabric, the textile can be laminated or otherwise combined with one or more additional layers, such as layers of one or more other textile materials (such as cotton or polyester). The resulting fabric can be used in a variety of apparel products (such as clothing and footwear), as well as other products (such as medical products). Embodiment

[0063] The following embodiments describe specific aspects of some implementations of the present disclosure to illustrate and provide a description for those of ordinary skill in the art. The embodiments should not be construed as limiting the present disclosure, as the embodiments only provide specific methods that can be used to understand and practice some implementations of the present disclosure.

[0064] Example 1 Spectrally Selective Textiles Using Inorganic-Organic Matrices for Passive Radiative Outdoor Personal Cooling Overview: Here, this embodiment demonstrates a radiative outdoor cooling textile using an inorganic-organic composite matrix. By reflecting more than about 90% of the solar irradiance and selectively transmitting the body heat radiation, this textile can make the heat generation rate of a simulated skin heater (about 104 W / m 2 ) comparable to that of the human body, thus avoiding overheating by about 5 to 13 °C compared with ordinary textiles (such as cotton) under peak sunlight conditions. Due to its excellent passive cooling ability and compatibility with mass production, this radiative outdoor cooling textile is expected to widely benefit society in many aspects.

[0065] Results and Discussion: Outdoor spaces are an inevitable part of daily life and can accommodate various essential physical activities. For example, it has long been recognized that outdoor leisure activities are crucial for maintaining personal physical and mental health. In addition, many occupations that make significant contributions to the social economy involve a large amount of outdoor labor, such as agriculture, landscaping, mining, construction, transportation, etc. However, one of the risks often encountered during outdoor activities is exposure to excessive heat stress. When the human body cannot effectively eliminate heat stress, hyperthermia occurs, leading to life-threatening clinical syndromes such as heatstroke, heat exhaustion, and heat cramps. It is reported that heat stress is the main cause of natural disaster deaths in the United States. The physiological and psychological effects of heat also lead to a reduction in industrial labor productivity and supply, which ultimately affects the overall economy and social welfare, especially in developing countries. Against the backdrop of global warming, the health and economic threats of outdoor heat stress to daily life as well as the occupational, sports, and military sectors will become more intense and frequent. A recent analysis estimates that by 2030, the annual cost of heat-related problems will reach approximately $2.4 trillion.

[0066] Therefore, outdoor cooling is required in many aspects, but due to its openness, it remains a great challenge. Different from indoor spaces where air conditioners can be easily implemented, using energy-intensive heating, ventilation, and air conditioning (HVAC) systems to cool large open spaces in the outdoor environment is impractical and uneconomical. In this case, the ideal solution is to cool the human body locally through clothing. Currently, the cooling technology for outdoor clothing involves moisture wicking, which promotes the removal of metabolic heat by pulling sweat from the skin to the outer surface of the fabric. Therefore, sweat evaporates more easily into the air than when it is trapped between the skin and the fabric. However, this technology relies on sweating, which involves the potential risk of dehydration and may lead to physical and mental deterioration or even death. In addition, its effect is severely limited when the humidity of the surrounding air is high enough to inhibit sweat evaporation. Other technologies for cooling clothing include incorporating phase change materials and the circulation of cold air or liquid. However, these technologies have some drawbacks that hinder their widespread adoption in the market, such as reduced mobility and discomfort due to the inclusion of bulky packaging or tubes, and high costs due to replenishment over time or power consumption.

[0067] Radiative cooling textiles are considered an attractive strategy because they utilize the body's inherent ability to emit thermal radiation without any energy input. For indoor environments, it has been demonstrated that infrared (IR) transparent textiles can passively provide significant personal cooling. However, due to a large amount of external heat from solar irradiance (about 1000 W / m 2 ) and significant in-body heat generation (about 100 W / m 2 ), outdoor radiative cooling textiles in direct sunlight face greater challenges.

[0068] Here, this embodiment demonstrates an improved concept of outdoor radiative cooling textiles with a solar irradiance reflectivity of over about 90% and a high transmittance to human thermal radiation. By embedding zinc oxide (ZnO) nanoparticles into nanoporous polyethylene (ZnO-PE), a combination of material properties and structural photon engineering is used to develop textiles with selective spectral responses. Experiments have shown that ZnO-PE can make the heat generation rate of a simulated skin heater comparable to that of human skin, about 104 W / m 2 , thus avoiding overheating by more than about 10 °C. Compared with ordinary textiles (such as cotton) in a typical outdoor environment with a peak solar irradiance of over about 900 W / m 2 , this is equivalent to over about 200 W / m 2Cooling power. In addition, when sweating evaporation takes effect, compared with cotton, the radiative cooling textile can still avoid the overheating of the simulated skin heater by about 8 °C. These results demonstrate the excellent ability to selectively adjust the radiative properties of textiles for passive outdoor cooling. Such improved textiles can enhance outdoor thermal comfort and attract more people to participate in outdoor activities.

[0069] The heat exchange between the human body and the outdoor environment is as Figure 3 shown in a. The total heat stress of the human body can be defined as: P 热应激 = P gen + P 阳光 - P rad - P evap - P conv - P cond where P gen is the heat production rate of metabolism, P 阳光 is the heat acquisition rate from solar irradiance, and P rad , P evap , P conv and P cond are the net heat loss rates through radiation, evaporation, convection, and conduction, respectively.

[0070] Therefore, maintaining outdoor thermal comfort involves reducing heat stress by reducing heat acquisition and increasing heat loss. Comparative methods mainly focus on the evaporative and convective heat losses of clothing to achieve outdoor cooling, but both of these heat dissipation paths have their own constraints, which largely depend on environmental conditions such as humidity and wind level. Although solar irradiance and thermal radiation contribute significantly to the overall heat exchange, they are rarely considered for textiles. As Figure 3 shown in c, the solar irradiance spectrum (AM 1.5G) is mainly distributed in the visible and near-infrared ranges of approximately 0.3 to approximately 4 μm, with a total power density of approximately 1000 W / m 2 . Based on its average solar reflectance value ( Figure 7 ), more than approximately 60% of the total solar irradiance can be absorbed by bare skin. On the other hand, human skin is a good IR emitter, with an IR emissivity of approximately 0.98 ( Figure 7 ). At a skin temperature of approximately 34 °C, the thermal radiation emitted by the human body is mainly in the mid-infrared range of approximately 7 to approximately 14 μm, with a peak emission wavelength of approximately 9.5 μm and a net radiative power density of approximately 100 W / m 2 . The average solar reflectance of ordinary textiles (such as cotton (white)) is approximately 60%, thus allowing a large portion of the solar irradiance power to be absorbed by the skin ( Figure 8 ). At the same time, the low IR transmittance of cotton hinders the effective loss of human thermal radiation ( Figure 8)。Due to the marginal overlap between solar irradiance and the human body's thermal radiation spectrum ( Figure 3 c), a spectrally selective radiative textile has been proposed that has strong solar reflectance and high mid-infrared transmittance to simultaneously reduce the input of radiative heat transfer and enhance its output for outdoor cooling.

[0071] Figure 3 Figure b shows a schematic of the proposed outdoor radiative cooling textile, which consists of ZnO nanoparticles (NP) embedded in a nanoporous PE (nanoPE) matrix. Polyethylene, which is composed of aliphatic C-C and C-H bonds, is IR transparent and thus can largely transmit human radiation sufficiently for indoor cooling. However, due to its relatively low refractive index n (about 1.5), its solar reflectance ratio is not satisfactory for outdoor applications. Inorganic solids generally have a higher refractive index than polymers, and among them, ZnO has a high refractive index n (about 2) and also has a small absorption from the visible light (about 400 nm) to the mid-infrared wavelength (about 16 μm). Their material properties make the combination of ZnO and PE particularly suitable as a base material to construct the required radiative selectivity for outdoor cooling purposes.

[0072] Numerical optimization of the inorganic-organic matrix design using structural photon engineering is carried out to obtain spectrally selective radiative properties. Figure 4 Figure a simulates the normalized scattering cross-section of spherical ZnO particles in a PE medium at spectral wavelengths from 0.4 to 16 μm with particle diameters in the range of 0.01 to 10 μm. When the particle size is less than 0.1 μm or greater than 1 μm, the scattering cross-section is either all small or all large throughout the wavelength range, resulting in low spectral selectivity. In the particle size range of 0.1 to 1 μm comparable to the solar wavelength, strong Mie scattering occurs, resulting in a selectively significant increase in the scattering cross-section in the visible and near-IR ranges, while the scattering in the mid-IR remains small. This result indicates that an appropriate selection of the ZnO particle size within about 0.1 μm to about 1 μm can achieve high reflectance in the visible and near-IR and high transmittance in the mid-IR. Additionally, at the same diameter (e.g., 320 nm, Figure 4 b), the scattering cross-sections of ZnO particles and pores in a PE medium are compared. The comparison shows that ZnO particles scatter more strongly in the visible range than pores, which further illustrates the advantage of ZnO in obtaining a higher visible light reflectance ratio. Finally, detailed calculations are carried out to determine the effects of ZnO particle size and density on solar reflectance ( Figure 4 c) and mid-IR transmittance ( Figure 4 d). As the particle size and density increase, the solar reflectance increases while the mid-IR transmittance decreases, resulting in Figure 4 the optimal range (white area) projected in Figure e.

[0073] According to the guidance of numerical optimization, ZnO-PE textiles were experimentally fabricated by the following method: ZnO particles were mixed with molten polyethylene at a weight ratio of ZnO:PE = approximately 2:5 in paraffin oil (the ratio of PE to oil was approximately 1 to 5), then the composite mixture was melt-pressed into a film, and finally the paraffin oil was extracted from the film with dichloromethane. The resulting ZnO-PE film was white in sunlight ( Figure 5 a), indicating strong scattering of all visible light at all angles. Examination under a scanning electron microscope (SEM) showed the porous structure of the textile (the pores accounted for approximately 20% to approximately 30% of the volume), where ZnO particles were randomly embedded in the PE matrix ( Figure 5 d-f). X-ray computed tomography of the textile sample using an X-ray microscope showed that ZnO particles were generally evenly distributed throughout the volume ( Figure 5 b). Their diameters were characterized using dynamic light scattering, mainly between approximately 0.3 and approximately 0.8 μm, and a peak appeared at approximately 0.5 μm ( Figure 5 b), matching the numerically optimized particle size.

[0074] The optical properties of ZnO-PE were measured using an integrating sphere with ultraviolet-visible-near-infrared (UV-VIS-NIR) and Fourier transform infrared (FTIR) spectrometers. The measured spectra showed a high reflectivity of more than approximately 90% in the sunlight region and a high transmittance of approximately 80% between approximately 7 and approximately 14 μm where human body heat radiation is concentrated ( Figure 5 g). The measured spectra were in excellent agreement with the theoretical simulation results ( Figure 9 ), verifying the strategic selection of appropriate materials and the rational structural photon design for achieving such spectral selectivity properties, thus meeting the standards for radiative outdoor cooling textiles.

[0075] To achieve the purpose of outdoor human body cooling, the textiles used themselves had very low thermal radiation (instead, high heat transfer) and strong sunlight reflection. Its radiative properties were completely different from other radiative cooling methods, and the method here further emphasized the various opportunities for radiative cooling depending on the nature of the application. More importantly, the method was specifically designed for textile applications, and its unique property was that the material could be extruded into fibers for knitting or weaving textiles ( Figure 5 c).

[0076] The outdoor performance of ZnO-PE radiative cooling textiles was demonstrated on a clear spring day in Stanford, California. Figure 6The measuring device shown in a) includes: a heater that mimics skin, which is placed on top of the foam to prevent heat loss to the bottom; a thermocouple that is on the surface of the heater for measuring the temperature of the mimicked skin; and a textile sample that covers the mimicked skin. Figure 6 b). A thermal power input of about 104 W / m 2 is applied to the heater to simulate the heat production rate of skin metabolism. The real-time temperature of the heater of the mimicked skin was recorded for about four hours around noon while the entire device was under direct sunlight and exposed to the air. As Figure 6 shown in c, around 13:00 (local time), under wind convection and a peak solar irradiance of about 910 W / m 2 , the heater of the mimicked skin covered with ZnO-PE showed a temperature of about 33.5 °C, much lower than that of the heaters of the mimicked skin covered with white cotton (45.6 °C) and bare (53.1 °C). Note that the temperatures of these heaters of the mimicked skin without textile samples were the same under sunlight and in the shade Figure 10 , which confirmed that the measured temperature differences came from the influence of the textiles. The significantly lower temperature of the heater of the mimicked skin covered with ZnO-PE demonstrated the excellent cooling ability of ZnO-PE, which was attributed to its high solar light reflection reducing the heat input from the sun and its high transmission of human body heat radiation enhancing the radiant heat output. Using heat transfer model analysis, the additional cooling power required for these textile samples to reach a normal skin temperature of about 34 °C under the test conditions in Figure 6 c was calculated (Supplementary Note, Figure 11 and 12 ). From 11:00 to 15:00 (local time), the heaters of the mimicked skin covered with cotton and bare were respectively specified with an additional cooling power of about 116 to about 219 W / m 2 and about 305 to about 454 W / m 2 , while ZnO-PE passive-cooled the heater of the mimicked skin to maintain the temperature below about 34 °C without additional cooling power supply Figure 6 d).

[0077] It should be further considered that sweat evaporation can provide additional cooling power, which is estimated by the product of the water evaporation rate through the textile Figure 13 and the heat of vaporization of water (about 44 kJ / mol). However, the cooling power supply estimated by evaporation still could not compensate for the cooling power requirements of the heaters of the mimicked skin covered with cotton and bare under wind convection and a peak solar irradiance of about 910 W / m 2 Figure 6 f). The real-time outdoor measurement was under wind convection and a solar irradiance of about 900 to about 1050 W / m2 This was carried out under the condition that, considering the influence of sweat evaporation, there is a water-soaked porous layer on the top of the heater ( Figure 6 e). With the addition of the sweat evaporation effect, ZnO-PE still maintained the temperature of the heater simulating the skin at about 34 °C, while in the cases of being covered with cotton and being bare, overheating of about 5 to about 8 °C and about 9 to about 15 °C was observed respectively, which is consistent with the thermal analysis results, further confirming the superiority of radiative cooling in outdoor environments.

[0078] The influence of the ZnO-PE layer thickness on sunlight reflection and mid-infrared transmission also needs to be considered ( Figure 14 ). As the thickness of the nanocomposite layer increased in the range of about 10 μm to about 640 μm, a trade-off was observed, where a thickness of about 80 μm to about 160 μm is optimal for both high sunlight reflection and mid-infrared transmission.

[0079] In addition, the stability and durability of the ZnO-PE textile material were evaluated by measuring the concentration of Zn ions in water before and after washing using inductively coupled plasma mass spectrometry ( Figure 15 ). The results showed that during the washing process, trace amounts of ZnO (about 2 parts per billion (ppb)) were released into the water. Due to the tight wrapping of PE around the ZnO particles, the good durability of the embedded structure was demonstrated. Similarly, the measurement results using 1 1H nuclear magnetic resonance (NMR) confirmed that dichloromethane is very volatile and can be removed substantially completely by evaporation ( Figure 16 ).

[0080] In addition, black was achieved by adding micron-sized silicon particles to the PE, which also showed high infrared transparency in the wavelength range of about 4 to about 18 μm ( Figure 17 ).

[0081] In summary, this example presents that ZnO-PE textiles with spectral selective radiation properties are beneficial for passive outdoor cooling of the human body through the combination of material properties and structural photon engineering techniques. The significant outdoor cooling performance demonstrated here under peak daylight conditions shows the prominent position of the passive radiative heat dissipation mechanism (a property lacking in ordinary textiles) in coping with the increasing challenges of outdoor heat stress and climate change. Another advantage of ZnO-PE includes its practical compatibility with large-scale manufacturing. Like other synthetic textile materials (such as nylon and polyester), wear resistance improvement treatments can be applied to ZnO-PE to enhance the wearing comfort in actual use. Further engineering the fiber geometry of ZnO-PE to endow it with moisture absorption and sweat wicking properties can achieve the synergistic effect of radiative and evaporative heat dissipation.

[0082] Materials and Methods: Manufacture of ZnO - PE Radiative Outdoor Cooling Textiles The ZnO-PE composite material was fabricated by the following method: ZnO particles (about 99.9%, Sigma Aldrich) were mixed with high-density polyethylene (HDPE, melt index about 2.2 g / 10 min, Sigma Aldrich) and ultra-high molecular weight polyethylene (UHMW, Alfa Aesar) in paraffin oil at a temperature of about 200 °C in a weight ratio of ZnO:HDPE:UHMWPE = about 2:4:1. The volume of paraffin oil was about 5 times the weight of the polyethylene. Then the mixture was melt-pressed into a film at about 70 °C to about 100 °C. Finally, paraffin oil was extracted from the film using dichloromethane (about 99.99%, Fisher Chemical). The ZnO-PE fibers were melt-extruded using a commercial extruder.

[0083] Material Characterization SEM images were taken by FEI Sirion (5 kV). X-ray computed tomography was performed using a ZEISS Xradia 520 Versa X-ray microscope. The ZnO particle diameter distribution curve was characterized using a Malvern Zetasizer Nano ZS. UV-VIS-NIR reflectance and transmittance were measured using an Agilent Cary 6000i UV-VIS-NIR spectrophotometer with a diffuse integrating sphere. IR reflectance and transmittance were measured using an FTIR spectrometer (Model 6700, Thermo Scientific) together with a diffuse gold integrating sphere (PIKE Technologies).

[0084] Outdoor Thermal Measurement A flexible heater insulated with silicone rubber (Omega, about 39 cm 2 ) was used to simulate the skin. The heater was connected to a power supply (Keithley 2400), which provided about 104 W / m 2The heating power density was used to simulate the heat production rate of metabolism. Insulating foam was placed beneath the heater that simulated the skin to ensure that the heat generated by the skin heater was selectively transferred to the surrounding environment. A strip thermocouple (with a diameter of approximately 0.3 mm, type K, Omega) was brought into contact with the top surface of the heater to measure the simulated skin temperature. The textile sample was covered on the heater that simulated the skin. The entire device was supported by a wooden frame covered with a layer of aluminized polyester film. During the test, the device was exposed to direct sunlight and air. The real-time temperatures of the heaters that simulated the skin covered with ZnO-PE, cotton, and uncovered were measured, as well as the ambient temperature. A pyranometer (Kipp&Zonen CMP 6) was used to record the direct and diffuse solar irradiance. To measure the sweat evaporation effect, an aluminum foam coated with a thin layer of carbon was soaked with water, sealed with a polydopamine-coated nanoPE film, and then placed on top of the heater to simulate the sweat evaporation effect.

[0085] Water Evaporation Rate Test This test procedure was based on the modified ASTM E96. Approximately 40 mL of distilled water was filled into a medium bottle (Fisher Scientific) of about 100 mL, and then sealed through the textile sample using an open bottle cap and a silicone rubber gasket (Corning). Then the sealed bottle was placed in an environmental chamber. The temperature and relative humidity in the chamber were maintained at approximately 35 °C and 30 ± 10% respectively. The total mass of the bottle and the sample together was measured regularly. Then the reduced mass (corresponding to the evaporated water) was divided by the exposed area (with a diameter of approximately 3 cm) and time to obtain the water evaporation rate.

[0086] Modeling of Transmission and Reflection of Polyethylene Embedded with ZnO To simulate light transmission and reflection, the PE material embedded with ZnO was modeled as a random medium containing uniformly distributed scattering particles. The Mie theory can be used to calculate the light scattering characteristics of individual ZnO nanoparticles. The optical parameters of ZnO for the calculation can be found in W.L. Bond, “Measurement of the Refractive Indices of Several Crystals,” Journal of Applied Physics 36, 1674 (1965), and M.R. Querry, “Optical constants” (MISSOURI UNIV-KANSAS CITY, 1985). The scattering cross-sections of particles with different sizes at different wavelengths were calculated. To simulate multiple PEs embedded with ZnO nanoparticles, the scattering cross-sections were averaged according to the normal distribution of the ZnO particle sizes with a variance of ±0.1 μm.

[0087] The Chandrasekhar radiative transfer theory can be used to simulate the light transmission through such a random medium. ZnO nanoparticles are modeled as isotropic scattering, which is a good approximation because each ZnO particle can have a different shape, but the macroscopic average optical properties affect the performance of the textile. The transmission through a slab region containing scattering particles can be obtained by the following equation: where ρ is the density of ZnO nanoparticles, σ avg is the average scattering cross-section, and h is the thickness of the material.

[0088] Equation (1) applies to the case where a slab region in an infinite host medium is embedded with scattering particles. Considering that the PE embedded with ZnO is a thin film structure suspended in air, the total transmission T 总 is calculated by multiplying the transmission T f of the thin film structure as an effective medium alone by the transmission obtained in Equation (1), i.e.: T 总 = T f ·T sca (2) Since the material absorption is very small and can be neglected in the wavelength range of interest, therefore, the total reflection of the PE film embedded with ZnO is calculated as R 总 = 1 – T 总 .

[0089] Supplementary Note: Thermal Transfer Model Analysis of Additional Cooling Power Requirements A one-dimensional steady-state heat transfer model analysis is used to determine the additional cooling power ( Figure 11 ) required for the skin to reach a skin temperature of 34 °C under outdoor conditions. In this model, the heat gain of the human body comes from solar irradiance and metabolic heat production. Heat radiation, conduction, and convection are included to simulate the heat dissipation from the clothed human body to the surrounding air ( Figure 7 ).

[0090] For the skin covered with textiles, the energy balance equations at the skin surface and the outer surface of the textile can be expressed as: At the skin surface: At the outer surface of the textile: The temperature profile inside the textile can be approximated as: For the bare skin, the energy balance equation at the skin surface is: qgen -q cool = -(1 - ρ 皮肤 , vis)·q 阳光 +q rad，皮肤 -q rad，amb +q conv (6) Here, q gen is the heat production rate of metabolism per unit area, q cool is the additional cooling power supply. q rad,皮肤 is the radiant heat flux from the skin, q rad,amb is the radiant heat flux from the surrounding air, q rad,ti is the radiant heat flux from the inner surface of the textile, qrad,to is the radiant heat flux from the outer surface of the textile, qcond, air is the conductive heat flux in the air gap between the skin and the textile, and qconv is the convective heat flux from the textile to the surrounding air. According to Fourier’s law, Newton’s law of cooling, and the Stefan-Boltzmann law, the conductive, convective, and radiant heat flux terms can be expressed as: q rad，皮肤 = σT 皮肤 4 (7) q rad，amb = ε amb σT amb 4 (8) q rad，ti = ε 纺织品，ir σT ti 4 (9) q rad，to = ε 纺织品，ir σT to 4 (10) q conv = h·(T to - T amb ) (12) All input parameters are listed in Table 1 below.

[0091] Table 1. Input parameters for heat transfer model analysis

[0092] During the outdoor thermal test, no additional cooling power is provided, i.e., q cool = 0. Using Figure 6 P measured in 阳光 , T 皮肤 and Tamb value, in the case of bare skin, the convective heat transfer coefficient h at different times during the test was fitted using Equation (6). Using the fitted convective heat transfer coefficient h values, the skin temperatures in the cases of ZnO-PE and cotton were calculated, and these temperatures were in very good agreement with the measured skin temperature values ( Figure 12 ). This result confirmed the applicability of the heat transfer model analysis. By substituting T 皮肤 = 34 °C and all other given input parameters into Equations (3), (4), (5) and (6), the additional cooling power q Figure 6 to maintain the skin temperature at 34 °C under the test conditions shown in cool .

[0093] Example 2 Coloring of Infrared-Transparent Polyethylene Textiles for Passive Radiative Cooling Overview: Effectively regulating the heat flow between the human body and the environment not only improves thermal comfort but also presents an improved and cost-effective method for reducing building energy consumption. Infrared performance-engineered textiles have been demonstrated to passively regulate radiative heat dissipation for effective human cooling and warming. However, allowing simultaneous control of visible color without compromising the required infrared performance remains a major challenge, which largely limits their attractiveness in practical applications. Here, this example reports a strategy that uses inorganic nanoparticles as coloring components instead of dye molecules and polyethylene as a flexible matrix to fabricate visibly colored and infrared-transparent textiles through a large-scale industrial process. The fabricated composite textiles show a high infrared transparency of about 80%, a passive cooling effect of about 1.6 to about 1.8 °C, and also show strong visible colors and good washing stability. This simple coloring method can promote the commercialization of radiative textiles in temperature-adjustable wearable applications to effectively save energy.

[0094] Results and Discussion: Managing the heat flow on wearable products is an important function for improving human health and comfort. In addition, considering the huge energy consumption in space heating and cooling, and for example accounting for more than 10% of the total energy consumption in the United States, heat management wearable products can have a substantial impact on building energy savings. With the increase in population and living standards, this is needed to alleviate the growing energy demand and climate change problems. In contrast to building-level temperature regulation (where most energy is wasted in empty spaces), personal heat management strategies are a more efficient and cost-effective solution that aims to provide local heating and cooling for the human body and its local environment.

[0095] Controlling the infrared (IR) properties of clothing textiles can have a strong impact on local cooling and heating of the human body. For example, it has been demonstrated that IR-transparent nanoporous polyethylene (nanoPE) can passively cool the human body by approximately 2 °C, while metallized nanoPE with a low IR emissivity can heat the human body by approximately 7 °C. This is because human skin has a high emissivity (ε = approximately 0.98) and acts like a black body, strongly emitting thermal radiation in the IR wavelength range of approximately 7 to approximately 14 μm, with a peak intensity of approximately 9.5 μm. Therefore, the thermal radiation path plays an indispensable role in human heat dissipation, accounting for more than approximately 50% under indoor conditions. These findings open a direction for personal thermal management, as contrasting textile materials lack the ability to control infrared radiation.

[0096] However, the limitation of IR properties poses great difficulties in simultaneously controlling the visible color appearance. Since color is one of the most important factors governing the wearable market, this challenge remains a major obstacle restricting its practical application in real life. The challenge lies in the fact that organic fabric dye molecules have different types of chemical bonds that can strongly absorb human radiation, such as C-O stretching (approximately 7.7–approximately 10 μm), C-N stretching (approximately 8.2–approximately 9.8 μm), aromatic C-H bending (approximately 7.8–approximately 14.5 μm), and S=O stretching (approximately 9.4–approximately 9.8 μm). Therefore, adding organic dyes may lead to a decrease in IR transparency, making it unsuitable for radiative cooling effects. In addition, polyethylene (the base material of radiative textiles) is chemically inert and has no polar groups, which inhibits the surface adhesion of chemical dyes.

[0097] In this example, the challenge between visible coloring and IR property control is addressed, and a demonstration of colored polyethylene textiles with high IR transparency for radiative cooling is reported. This is achieved by successfully identifying and utilizing inorganic pigment nanoparticles with negligible absorption in the IR region, while reflecting certain visible colors by optimizing the concentration and size. Instead of unstable surface adhesion methods, the inorganic pigment nanoparticles are compounded into the polyethylene matrix to form a substantially uniform composite for stable coloring. It is further demonstrated that the colored polyethylene composite can be easily extruded into continuous and mechanically strong fibers for weaving interlaced fabrics using a large-scale process. The woven fabric shows a high IR transparency of approximately 80% and good radiative cooling performance of approximately 1.6 to approximately 1.8 °C, as well as good color stability in water for the washing cycle. This approach lays the foundation for the practical implementation of radiative textiles to provide improved personal thermal management for more efficient energy utilization.

[0098] A schematic diagram of the proposed design of the colored polyethylene textile is as Figure 18As shown in Fig. a. Inorganic nanoparticles that are IR transparent are selected as pigments, and polyethylene is selected as the flexible polymer matrix or host. These two components are uniformly mixed through a mixing process, and then the resulting composite material can be extruded into fiber shapes for weaving or knitting into interwoven fabrics. As Figure 18 As shown in Fig. b, inorganic solids found to meet the IR transparency criteria include Prussian blue (PB), iron oxide (Fe2O3), and silicon (Si), which are also non-toxic and inexpensive for use in textiles. Figure 18 Fourier transform infrared (FTIR) spectroscopic measurements in Fig. c show that the absorbance of these inorganic solids is negligible in the infrared wavelength range of approximately 4 - 14 μm, with the exceptions being the strong and narrow peak of Prussian blue at approximately 4.8 μm (due to C≡N stretching vibrations) and the weak and broad peak of silicon at approximately 8 - 10 μm (due to native silica on the surface). As Figure 18 As shown in the scanning electron microscope (SEM) images in Figs. d - f, their particle sizes are selected in the range of approximately 20 nm to approximately 1000 nm. On the one hand, this nanoscale size range is much smaller than the human body's thermal radiation wavelength of approximately 4 - 14 μm. Therefore, these nanoparticles will not cause strong scattering of infrared light, thus reducing the IR transparency of the colored polyethylene mixture. On the other hand, based on Mie scattering theory, dielectric or semiconductor nanoparticles with a high refractive index within a specific size range can have strong resonant light scattering in the visible spectral range. Therefore, different visible colors can be produced by controlling the nanoscale size. For example, in contrast to the black color of bulk silicon, silicon nanoparticles with a diameter of approximately 100 nm to approximately 200 nm (refractive index > approximately 3.8 at 633 nm) exhibit a yellow color due to an obvious Mie resonance response associated with the excitation of magnetic and electric dipole modes. Different from silicon nanoparticles, bulk Prussian blue and iron oxide nanoparticles both show their natural colors. The dark blue color of Prussian blue is related to the intervalence charge transfer between Fe(II) and Fe(III), while the deep red color of iron oxide is determined by its optical bandgap of approximately 2.2 eV. Using these three primary colors of blue, red, and yellow, all different colors can be created across the visible spectrum by mixing them in different proportions.

[0099] The nanoparticles are physically mixed with molten polyethylene particles at approximately 180 °C using a mixing process to produce a substantially homogeneous inorganic solid - polymer composite material. The optimal mass ratio of the nanoparticles is approximately 1%, and this composite material maintains good thermoplastic processing properties for shaping into any shape and has satisfactory optical properties in both the visible and infrared ranges. Due to the substantially uniform distribution of the pigment nanoparticles within the polyethylene polymer matrix, PB - PE, Fe2O3 - PE, and Si - PE composite films with a thickness of approximately 100 μm respectively show uniform and intense blue, red, and yellow( Figure 19a). The ultraviolet-visible (UV-VIS) spectroscopy measurement of the composite film shows that the main reflection wavelengths are at about 450 nm, about 600 nm, and about 750 nm, respectively, which match the original colors of Prussian blue, iron oxide, and silicon nanoparticles ( Figure 19 b). The strong reflection and absorption of visible light result in a high opacity (designated as 1 - specular transmittance) in the visible range exceeding about 80% ( Figure 19 d), which meets the basic function of clothing in preventing the identification of objects behind textiles. In addition, in the infrared region, the composites all show a high transmittance of about 80% ( Figure 19 c), enabling the transfer of human body radiant heat to the environment to achieve a radiative cooling effect.

[0100] This is further demonstrated by extruding the colored polyethylene composite into a multi-filament yarn using a high-throughput melt spinning machine ( Figure 20 a). As Figure 20 shown in the optical microscope images of c - e, each extruded yarn consists of 19 mono-filament fibers with a diameter of about 30 to about 50 μm. It is also evident that the pigment nanoparticles are generally evenly embedded within the fibers. In addition, mechanical strength tests show that the maximum tensile force that the colored polyethylene composite yarn can withstand is about 1.9 N to about 2.8 N, which is comparable to the cotton yarn used in ordinary clothing fabrics ( Figure 20 b). This mechanical strength allows the yarn to be further woven into a large-scale interwoven fabric with good breathability, softness, and mechanical strength ( Figure 20 f - k). With the incorporation of the interwoven weaving pattern, the colored polyethylene composite fabric still shows a high infrared transmittance of about 80% ( Figure 21 a), which is roughly the same as the infrared transmittance of the planar solid film shown in Figure 19 c. In addition, the stability and durability of the colored polyethylene fabric are evaluated by measuring the concentrations of Fe, K, and Si ions in water before and after washing using inductively coupled plasma mass spectrometry ( Figure 21 b). The negligible change in ion concentration proves that the Fe2O3, Prussian blue, and Si nanoparticles are tightly wrapped by the polyethylene polymer matrix, and can withstand the washing cycle and maintain the original color without releasing the pigment nanoparticles into the water.

[0101] Finally, the thermal properties of the colored polyethylene textiles are characterized. A rubber-insulated flexible heater is used to simulate the heat generation of the skin, and its temperature response is recorded when covering different textile samples. The entire device is enclosed in a room where the ambient air temperature is generally maintained constant at about 25 °C. At about 80 Wm equivalent to the heat generation rate of human metabolism -2When the skin heater has a thermal power density of, the exposed skin heater shows a temperature of about 33.5 °C. When the skin heater is covered with ordinary cotton textiles, the skin temperature rises to about 36.5 °C( Figure 21 c). When covered with PB-PE, Fe2O3-PE, and Si-PE textiles, the measured skin temperatures are in the range of about 34.7 to about 34.9 °C, indicating that compared with cotton, they have the ability to passively reduce the human body temperature by about 1.6 to 1.8 °C. When the colored polyethylene textiles are worn on the human skin, the radiative cooling effect is visualized and verified using an infrared camera( Figure 21 d). The comparison conducted under thermal imaging clearly shows that the colored polyethylene textiles allow better transfer of human radiative heat to the environment than ordinary cotton textiles.

[0102] In summary, this example demonstrates an improved method based on inorganic pigment nanoparticles for large-scale manufacturing of visibly colored and infrared-transparent textiles, which allows for more efficient dissipation of human radiative heat compared to comparative textiles and exhibits attractiveness in a variety of colors. It is found that pigment materials including Prussian blue, iron oxide, and silicon can meet all the conditions of negligible IR absorption, non-toxicity, and low cost, and they can produce primary colors of blue, red, and yellow respectively. By mixing these three primary colors in different ratios, different colors spread across the entire visible spectrum can potentially be created. Through a large-scale mixing, extrusion, and weaving process with optimal nanoparticle concentration and size, the fabricated composite textiles show strong visible coloring, high infrared transparency of about 80%, passive cooling effect of about 1.6 to about 1.8 °C, and good washing stability. The method introduced in this paper solves the key bottleneck of radiative textile coloring and contributes to the advancement towards the application of energy-efficient and cost-effective thermal management wearable technologies.

[0103] Materials and Methods: Textile Manufacture. The coloring of polyethylene is carried out by the following method: various inorganic solid pigment nanoparticles (such as Prussian blue (ACROS Organics), iron oxide (Sigma Aldrich, 99%), and silicon (MTI Corporation, 100 nm, 99%)) are mixed with molten high-density polyethylene pellets (melt index: about 2.2 g per 10 min, Sigma Aldrich) at about 180 °C using a twin-screw mixer (Polymers Center of Excellence). The optimal mass ratio between the nanoparticles and polyethylene is about 1:100. Then the nanoparticle-mixed polyethylene composite is extruded into fibers using a multifilament melt spinning machine (Hills Inc.). Textiles are woven using a FAK sampler loom at the Textile Technology Center of the University of Gaston.

[0104] Material Characterization. Photographs of the extruded fibers and woven textiles were taken using an optical microscope (Olympus). SEM images were taken using a FEI XL30 Sirion SEM (at approximately 5 kV). Infrared absorbance and transmittance were measured using an FTIR spectrometer (Model 6700, Thermo Scientific) together with a diffuse gold integrating sphere (PIKE Technologies). Visible reflectance and opacity were measured using a UV-Vis spectrometer (Agilent, Cary 6000i).

[0105] Thermal Measurement. A rubber-insulated flexible heater (Omega, approximately 72 cm 2 ) connected to a power supply (Keithley 2400) was used to simulate the skin. A strip thermocouple (with a diameter of approximately 0.3 mm, type K, Omega) was placed in contact with the upper surface of the simulated skin to measure the skin temperature. A protective heater and insulating foam were placed under the skin heater of the simulated skin to ensure that the heat generated by the skin heater was selectively transferred to the environment. The temperature of the protective heater was set to the same as that of the skin heater, thus avoiding downward heat conduction to the workbench. The entire device was enclosed in a chamber, and the ambient temperature in the chamber was controlled to be approximately constant at about 25 °C. The power density of the skin heater was set to be approximately constant at about 80 W m -2 , such that the skin temperature was about 33.5 °C at an ambient temperature of about 25 °C. When the skin was covered with a textile sample (approximately 5 × approximately 5 cm 2 ), the steady-state skin temperature response was measured while the ambient temperature was maintained at about 25 °C. Thermal images were taken using a calibrated thermal imager (MikroSHOT, Mikron).

[0106] Mechanical Testing . The tensile strength test was measured using an Instron 5565. The yarn samples were cut into lengths of approximately 4 cm. The gauge distance was approximately 2 cm long, and the displacement rate was maintained at about 10 mm min -1 .

[0107] Washing Test . The woven textiles were washed with clean water (approximately 80 ml) for about 30 min under stirring. The water before and after washing was collected and then tested using inductively coupled plasma mass spectrometry (ICP-MS) to quantify the amount of metal ions (K, Fe, and Si for Prussian blue, iron oxide, and silicon, respectively) released from the textile samples during washing.

[0108] As used herein, unless the context clearly indicates otherwise, the singular terms "a", "an", and "the" may include plural referents. Thus, for example, unless the context clearly indicates otherwise, a reference to an object may include a plurality of objects.

[0109] As used herein, the terms "substantially", "essentially", and "about" are used to describe and account for small variations. When used in conjunction with an event or circumstance, these terms can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs very nearly. For example, when used in conjunction with a numerical value, the terms can encompass a variation range of ±10% less than or equal to the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0110] As used herein, the term "size" refers to a characteristic dimension of an object. Thus, for example, the size of a spherical object can refer to the diameter of the object. In the case where the object is non-spherical, the size of the non-spherical object can refer to the diameter of a corresponding spherical object, where the corresponding spherical object exhibits or has a set of specific derivable or measurable properties that are substantially the same as those of the non-spherical object. When a group of objects is referred to as having a specific size, it is contemplated that the objects can have a size distribution around that specific size. When referring to a group of objects having a specific size, it is expected that the objects can have a size distribution around the specific size. Thus, as used herein, the size of a group of objects can refer to a typical size of the size distribution, such as an average size, a median size, or a peak size.

[0111] In addition, quantities, proportions, and other numerical values are sometimes presented herein in a range format. It should be understood that such range formats are used for convenience and brevity and should be interpreted flexibly as including the numerical values explicitly specified as the limits of the range, but also including all individual numerical values or sub-ranges subsumed within that range, as if each numerical value and sub-range were explicitly specified. For example, a range of from about 1 to about 200 should be understood to include the explicitly listed limits of about 1 and about 200, and also individual values (such as about 2, about 3, and about 4) and sub-ranges (such as from about 10 to about 50, from about 20 to about 100, etc.).

[0112] Although the present disclosure has been described with reference to specific embodiments thereof, those skilled in the art will understand that various changes can be made and equivalents can be substituted without departing from the true spirit and scope of the present disclosure as defined by the appended claims. Additionally, many modifications can be made to adapt a particular situation, material, composition of matter, method, operation to the purposes, spirit and scope of the present disclosure. All such modifications are intended to fall within the scope of the appended claims. In particular, although certain methods may have been described with reference to specific operations performed in a particular order, it should be understood that these operations can be combined, sub-divided or re-ordered to form equivalent methods without departing from the teachings of the present disclosure. Accordingly, unless specifically stated herein, the order and grouping of operations are not limitations of the present disclosure.

Claims

1. A textile, comprising: a substrate comprising polyethylene; A particulate filler, which is dispersed in the matrix, wherein the average particle size of the particulate filler is in the range of 500 nm to 900 nm, and the number density of the particulate filler is 0.1 to 0.5 μm -3 , wherein the particulate filler comprises zinc oxide, and wherein the relative difference in refractive index between the particulate filler and the polymer or mixture of polymers comprised in the textile is at least about ±1% relative to the refractive index of the polymer or mixture of polymers comprised in the textile for visible light; and inorganic pigment nanoparticles incorporated into the substrate to form a substantially homogeneous composite material for stable coloring; wherein the transmittance of infrared radiation of the textile at a wavelength of 9.5 μm is at least 40%; wherein the weighted average reflectance of radiation of the textile in the wavelength range from 0.3 μm to 2 μm is at least 40%, and wherein the thickness of the zinc oxide - polyethylene layer is from 80 μm to 160 μm.

2. The textile according to claim 1, wherein the variation range of the particle diameter is from 0.01 to 10 μm.

3. The textile according to claim 1, wherein the inorganic pigment nanoparticles comprise any one of Prussian blue (PB), iron oxide, and silicon.

4. The textile according to claim 1, wherein the inorganic pigment nanoparticles are incorporated into the substrate by mixing the inorganic pigment nanoparticles with molten polyethylene particles at about 180 °C.

5. The textile according to claim 1, wherein the inorganic pigment nanoparticles are incorporated into the substrate to produce an extruded multifilament yarn.

6. The textile according to claim 1, wherein the substrate is porous.

7. The textile according to claim 6, wherein the volume percentage of pores in the substrate is at least 5%.

8. The textile according to claim 6, wherein the average pore size of the pores in the substrate is in the range of 10 nm to 4000 nm.

9. The textile according to claim 1, comprising fibers, the fibers comprising the substrate and the particulate filler dispersed within the substrate.

10. The textile according to claim 1, comprising a film, the film comprising the substrate and the particulate filler dispersed within the substrate.

11. A method of regulating body temperature, comprising: placing the textile according to any one of claims 1 - 10 near the body.

12. A method of forming a porous textile, comprising: A mixture of a solvent, at least one polymer, and particulate filler is formed, wherein the at least one polymer includes polyethylene, the particulate filler includes an inorganic material, the inorganic material has a transmittance of infrared radiation at a wavelength of 9.5 μm of at least 40%, and the average particle size of the particulate filler is in the range of 500 nm to 900 nm, and the number density of the particulate filler is 0.1 to 0.5 μm -3 , wherein the particulate filler includes zinc oxide; extruding the mixture to form a textile comprising a solvent and the particulate filler dispersed within the textile; and extracting the solvent from the textile to form the porous textile, wherein the thickness of the zinc oxide - polyethylene layer is from 80 μm to 160 μm.

Images