A Janus Textile Capable of Radiative Subambient Cooling and Warming for Personal Thermal Management in Harsh Climates

doi:10.21203/rs.3.rs-2091852/v1

Download PDF

Article

A Janus Textile Capable of Radiative Subambient Cooling and Warming for Personal Thermal Management in Harsh Climates

https://doi.org/10.21203/rs.3.rs-2091852/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Textiles with radiative cooling/warming capabilities provide a green and effective solution to personal thermal comfort in different climate scenarios. However, developing multiple-mode textiles for wearing in harsh climates with large temperature variation remains a challenge. Here we report a Janus textile comprising a polyethersulfone (PES)-Al₂O₃ cooling layer optically coupled with a Ti₃C₂T_x warming layer, which can realize sub-ambient radiative cooling, solar warming and active Joule heating. Owing to the intrinsically high refractive index of PES and the rational design of the fiber topology, the nanocomposite PES textile features a record high solar reflectance of 0.97. Accompanied by an infrared emittance of 0.91 in the atmospheric window, sub-ambient cooling of 0.5-2.5 °C was achieved near noontime in humid summer under ~1000 W m^-2 solar irradiation in Hong Kong. The simulated skin covered with the textile was ~10 °C cooler than that with white cotton. The Ti₃C₂T_x layer provides a high solar-thermal efficiency of ~80% and a Joule heating flux of 66 W m^-2 at 2V due to its excellent spectral selectivity and electrical conductivity. The switchable multiple working modes enable effective and adaptive personal thermal management in different harsh environments.

Human body thermal regulation is critical for personal comfort and health during daily activities. Particularly, outdoor workers and sports enthusiasts usually have to expose their bodies to harsh climates with ambient temperatures much higher or lower than the comfort temperature (~25 °C); even worse, the changes in ambient temperature they experience within one day sometimes are very large, even as high as 20 °C, which are beyond the self-regulation ability of human bodies¹. Conventional clothes play very important roles in maintaining the body thermal comfort, which is realized by reducing the heat dissipation via convection and conduction. However, thermal radiation, which generally accounts for the most heat dissipation in human bodies²^,³, has been always overlooked in conventional textiles. Recently, artificially designed IR-transparent textiles have been developed to endow them with the intriguing capability of radiative cooling^4-7. These textiles made of nanoporous polymer membranes feature high transparency (~0.90) in the mid-IR region, allowing the rapid dissipation of body heat through radiation to the environment. However, they cannot realize sub-ambient cooling in the daytime under solar irradiation due to the inherent tradeoff between the solar reflectance and mid-IR transparency.

On the other hand, sub-ambient daytime radiative cooling has been achieved in deliberately designed nanophotonic coatings and films^8-15. They can strongly radiate the IR emission to the cold sky (down to 3 K) and gain negligible heat from the Sun due to their near-perfect solar reflectance (~0.95-0.98). Recently, two IR-emissive textiles with wearability and comfort have even been demonstrated to achieve surface temperatures below the ambient temperature under sunlight. One involved a multilayer IR-emissive metafabric that consisted of a TiO₂-polylactic acid (TiO₂-PLA) composite laminated with a commercial UV-reflective polytetrafluoroethylene (PTFE) layer, offering a solar reflectance of 0.924 and a mid-infrared emittance of 0.945¹⁶. The other IR-emissive textile was made of natural silk decorated with inorganic nanoparticles (~300 nm) to increase the UV reflection, showing an improved solar reflectance of 0.95 and a mid-infrared emittance of 0.90¹⁷. It is widely recognized that the solar reflection ability dominates the cooling effects of daytime radiative coolers, considering the intense solar irradiation (up to 1000 W m^-2). However, the solar reflectance of these two IR-emissive textiles was still inferior to those of their coating and film counterparts, which limited their cooling performance under intense sunlight and high humidity. In addition, current radiative cooling textiles are not suitable for wearing in cold environments or environments with large temperature changes. For personal thermal management in various climate scenarios, dual-mode textiles that can realize both subambient radiative cooling and warming are highly desirable. Although a few dual-mode textiles have been reported, they can only adjust the thermal radiation of human body, which are more applicable for indoor scenarios¹⁸^,¹⁹. Moreover, their fabrication process is complicated due to multilayer structures (>4 layers)¹⁸^,²⁰.

Here, to address the foregoing challenges, we proposed a Janus textile comprising two optically coupled layers, i.e., a solar reflective PES-Al₂O₃ fibrous textileand a thin IR-reflective Ti₃C₂T_x MXene coating (Fig. 1a). The IR-reflective MXene coating increases the optical path length of mid-IR light, and thus improves the emissivity of the thin textile to 0.91. Moreover, the electrospun PES-Al₂O₃ textile embraces a solar reflectance of 0.97, which is competitive against those of high-performance daytime radiative cooling coatings and films. This enhancement in solar reflection is realized by maximizing the Mie scattering efficiency over the full solar spectrum through the intrinsically high refractive index of PES (1.68) and the well-controlled fiber size distribution. As a result, the textile achieved temperatures of 0.5-2.5 °C below the ambient temperature under solar irradiation of around 1000 W m^-2, with a high relative humidity of 50%, at a summer noon in a subtropical coastal city, Hong Kong. In addition, the MXene layer on the other side with a high solar absorptance (0.85) and an intrinsically low MIR emittance (0.22) can harvest solar energy for personal warming in cold climates. When the solar radiation is unavailable or insufficient, the superior electrical conductivity of Ti₃C₂T_x MXene enables the warming side to serve as a Joule heater on any occasion. The cooling mode and heating mode can be easily switched by flipping over, making the Janus textile adaptive to different indoor and outdoor environments.

Optical properties and coupling effects of the Janus textile

Objects on the Earth emit infrared radiation through the atmospheric transmission windows (mainly within 8–13 µm) to the cold higher sky, and daytime sub-ambient cooling can be achieved with zero energy consumption when most solar radiation can be reflected^21,22. Although daytime sub-ambient radiative cooling has been achieved in multilayer photonic emitters^8,9,15, nannoporous polymer membranes^10,12−14 and even woods¹¹, few wearable textiles that can realize sub-ambient daytime radiative cooling have ever been reported^16,17. To achieve effective daytime radiative cooling in hot climates with high solar irradiance, the textiles should have a high solar reflectance (> 0.94) in practice considering variation in atmospheric conditions across different geographic areas⁸. Polymer nanofibers can scatter sunlight if the fiber diameters are carefully designed to allow their Mie resonance wavelengths to match the solar spectrum^13,23. However, in previous polymer nanofiber designs, the refractive index n of polymers, an important intrinsic optical property, is always overlooked, hindering the pursuit of solar reflectance of > 0.95. Here we selected PES that has one of the highest refractive index n of 1.68 among polymers to produce sub-ambient radiative cooling textiles^24,25. The extinction coefficient k of PES is zero in the visible region, indicating its negligible absorption (Supplementary Fig. 1). Besides, PES is widely used in water filtration and feeding bottles and proved to be harmless for human health^26–28.

The PES nanofiber-based textile was fabricated by the electrospinning technique (Fig. 2a). The textile consists of nanofibers with smooth surfaces (Fig. 2b). The higher-magnification scanning electron microscope images show there exist nanopores in fibers, which are formed while solvent dries out and air penetrates into fibers (Supplementary Fig. 2)²⁹. The very white color of the textile indicates its strong reflection to visible light. Referring to the Mie’s scattering theory, both the refractive index and the fiber diameters are the two key factors that dominate the Mie scattering efficiency of nanofibers. With the increase of the fiber diameter, the Mie resonance peak redshifts to longer wavelengths. To determine the optimal range of PES fiber diameters, we defined the average scattering efficiency $\overline {Q}$ weighted by the AM1.5 G solar spectrum (see Supplementary Eq. 5). The calculated results show that PES fibers with a diameter in the range of 0.5-1.0 µm have maximum scattering efficiency to the sunlight (Fig. 2c and Supplementary Fig. 3). By carefully controlling the electrospinning process, the textile with a desired fiber size distribution centered at 0.6 µm was successfully obtained, matching

the high $\overline {Q}$ (Fig. 2c). Furthermore, the influence of the refractive index n on $\overline {Q}$ was also investigated (Fig. 2d). The results indicate that the $\overline {Q}$ of polymer nanofibers strongly depends on their n, and nanofibers with larger n typically produce stronger solar scattering. For instance, a PES nanofiber (n = 1.68) of 0.6 µm has a $\overline {Q}$ of 2.64, which is 32% higher than that ($\overline {Q}$= 2) of a polyvinylidene fluoride (PVDF) fiber (n = 1.42) of the same diameter. In short, compared with most polymers (PVDF, PLA, etc., see Supplementary Table 1 for refractive index), PES nanofibers have higher average scattering efficiency over a wide diameter range. The origin of light scattering on scattering centers (such as fibers or particles) is attributed to the difference in n between the scattering centers and the environment (the air in this case). The PES fibers produce a high refractive index contrast ($\Delta n={n_{PES}} - {n_{Air}}=1.68 - 1=0.68$) across the fiber-air interfaces, leading to strong solar scattering. As a result, a solar reflectance ${\bar {r}_{0.3 - 2.5\mu m}}$ of 0.97 was achieved in a 600-µm-thick PES-based textile, which is the highest value ever reported in textiles and is competitive compared with the record of radiative cooling paints and films (Fig. 2e). The high refractive index n also makes PES textile more scattering to visible light and opaquer to human eyes compared with cellulose acetate (CA, n ~ 1.47) textile in wet state (Fig. 2f), which benefits privacy protection. The influence of nanopores inside fibers on the scattering efficiency was also explored. These nanopores with a comparable size range to UV light (10 to 400 nm) can enhance the averaged scattering efficiency of fibers in the UV range (Supplementary Fig. 4).

It is well-known that light will experience strong resonant absorption if the frequency of the light matches the vibrational frequency of the chemical bonds³⁰. Thus, PES, which has plenty of C-O (1324 − 1239 cm^− 1) and S = O (1144 − 1100 cm^− 1) bonds in its backbones (Supplementary Fig. 1), is an effective emitter material^31,32. As shown in Supplementary Fig. 5, the spectrally averaged emittance of the electrospun PES textile within 8–13 µm (${\bar {\varepsilon }_{8 - 13\mu m}}$) is 0.81, and there are four absorption drops centered at 9.5, 10.2, 10.8, and 13.0 µm, respectively. To enhance the ${\bar {\varepsilon }_{8 - 13\mu m}}$ of the textile, we incorporated Al₂O₃ nanospheres (20 nm in diameter) with a broad absorptance band centered at 880 cm^− 1 into PES nanofibers to construct a PES-Al₂O₃ composite textile^33,34 (5 wt.%, elemental mappings see Supplementary Fig. 6). It can be seen from Supplementary Fig. 5 that the emittance of the PES-Al₂O₃ textile in the range of 10–13 µm increases notably compared to the pure PES textile. As a result, the ${\bar {\varepsilon }_{8 - 13\mu m}}$ is improved to 0.91 (Fig. 2e). It should be mentioned that the Al₂O₃ additives in this work are only beneficial for enhancing the MIR emission. It almost has no effect on the solar reflection due to its very low concentration and small size.

For the warming side, Ti₃C₂T_x MXene nanoflakes were coated on one side of the PES-Al₂O₃ textile using a vacuum-assisted filtration method to serve as solar-absorbing materials (Fig. 2a Inset, see Supplementary Fig. 8 for its SEM image). The resultant black side embraces a high solar absorptance ${\bar {\alpha }_{0.3 - 2.5\mu m}}$ of 0.85 and a low emittance $\bar {\varepsilon }$ of 0.22 in the mid-infrared (MIR) range (Fig. 2g). Moreover, owing to the high electrical conductivity of Ti₃C₂T_x, the warming side can provide heat via Joule effect that is a reliable complement for solar heating. To keep the body warm in cold environments, the low MIR emittance (i.e., high MIR reflectance) is highly desired because of reduced thermal radiation to the surroundings and outer space. When paired with the radiative cooling side, it also enables the warming side (Ti₃C₂T_x) to reflect the unabsorbed portion of the incident MIR light strongly, which can be re-absorbed by the textile (see the inset of Fig. 2h). Thus, the cooling side and the warming side optically couple with each other instead of simply stacking, which enhances the optical path length of IR light and the ${\bar {\varepsilon }_{8 - 13\mu m}}$ of the cooling side remarkably (Fig. 2h). For instance, the ${\bar {\varepsilon }_{8 - 13\mu m}}$ of the Janus textile with a smaller thickness of 150 µm (0.83) is very close to that of the PES-Al₂O₃ textile with a thickness of 300 µm (0.85). Such an optical coupling effect helps the textile own a satisfactory MIR emittance with a thinner thickness, which improves the overall performance, including cooling effects, breathability, and light weight, of the textile to achieve better wearing comfort.

Sub-ambient Cooling And Skin Cooling Performance

Field tests were conducted to evaluate the cooling performance of our Janus PES-Al₂O₃/Ti₃C₂T_x textile in both daytime and nighttime (Fig. 3a). The tests were performed on summer days (July 2021) in Hong Kong (22°16′50′′ N, 114°10′20′′ E), a tropical and coastal city with a total precipitable water (TPW) value of ~ 60 mm. Since the textiles target at personal thermal management, the samples were directly exposed to the ambient air without any solar

shading or convection cover to mimic the real practical scenario. A weather station was used to monitor the climate data near the samples in real-time. T-type thermocouples were attached on the backside of the samples placed on the EPS foam with a density of 25 kg m^− 3 (Fig. 3b). Promisingly, sub-ambient cooling of 0.5–2.5°C was achieved at noon under a solar irradiation of 900–1000 W m^− 2 (Fig. 3c,d and Supplementary Fig. 9a). In the afternoon, our textile can achieve ~ 3.4°C maximum temperature drop (ΔT) relative to the ambient with a RH of ~ 50%. To the best of the authors’ knowledge, this was the first time for textiles directly exposed to the ambient to achieve sub-ambient cooling in subtropical coastal regions under strong solar irradiation and high RH. During the nighttime, a larger ΔT of ~ 4.7°C was achieved with RH of more than 80% (Fig. 3e,f and Supplementary Fig. 9b). These results validate the superior all-day sub-ambient cooling performance of our textile even under weather conditions of high RH and strong solar irradiation.

Further, a simulated human skin was used to assess the cooling performance of the textile as clothes (Fig. 3g). The simulated human skin is composed of a silicone rubber heater and a 3M tape²⁰ (3M micropore 1533-1), which has quite similar spectral characteristics within 0.3–16 µm to real human skin (Supplementary Fig. 10 and Supplementary Table 2). The input power of the silicone rubber heater was set to 100 W m^− 2 referring to the human basal metabolic rate (BMR)³⁵. White cotton, which has better radiative cooling performance (${\bar {r}_{0.3 - 2.5\mu m}}=0.68$, and ${\bar {\varepsilon }_{8 - 13\mu m}}=0.90$) than other common textiles, such as spandex, chiffon, and linen¹⁶. was also measured as a reference (see Supplementary Fig. 11a and Supplementary Table 3 for its optical performance). During the daytime measurement, the temperature of the simulated skin covered with our textile is 3–10°C lower than that covered with white cotton due to its higher ${\bar {r}_{0.3 - 2.5\mu m}}$ and ${\bar {\varepsilon }_{8 - 13\mu m}}$ (Fig. 3h and Supplementary Fig. 9c). The highest temperature difference of 10.2°C was observed at noon with peak solar irradiation of ~ 1000 W m^− 2. Moreover, the temperature difference between our textile and the bare simulated skin was 10–19°C during the daytime, showing remarkable cooling effects. This skin cooling performance exceeds those in previous literature^16,20. To demonstrate the performance of the large-size textile in real scenarios, we sewed a PES-Al₂O₃ textile and a white cotton T-shirt together (Fig. 3i). A body model with uniform temperature distribution was designed and prepared for the field test (Supplementary Fig. 13). The model dressed in the T-shirt was placed on the rooftop under direct sunlight (solar intensity ranged from 630 W m^− 2 to 930 W m^− 2). The IR image shows the surface temperature of the PES-Al₂O₃ textile is ~ 4°C below that of the white cloth under solar irradiation of ~ 700 W m^− 2 (Fig. 3i). The skin temperature under the PES-Al₂O₃ textile is 2.1–5.4°C lower than that of the other side covered by the cotton cloth (Supplementary Fig. 14). This experiment verifies that the cooling textile is more comfortable to wear outside with strong sunlight compared to conventional white cotton.

Solar Heating Performance

The solar heating performance of the warming side of the Janus textile was tested on the simulated skin in an environmental control room (Supplementary Fig. 15, L×W×H, 8×4×3 m³, accredited by ISO/IEC 17025:2017) under different ambient temperatures and solar intensities. Commercial black cotton with both high sunlight absorptance (0.65) and high IR emittance (0.90) was also tested for comparison. As shown in Fig. 4a and Supplementary Fig. 16, the surface temperature of our textile was 6–21°C higher than that of the black cotton when the solar intensity changed from 0.2 to 0.8 sun (1 sun = 1000 W m^− 2). The calculated net heating power of the black cotton is 41–53% lower than that of the Janus textile (Supplementary Fig. 18, see Supplementary Note 2 for the heat transfer model). Unlike black cotton, the temperature of the simulated skin covered with our textile can be maintained above 33°C (normal temperature of human skin) under most test conditions (Fig. 4b and Supplementary Fig. 19). For example, a solar intensity of 0.4 sun (a typical value in sunny winter days) is sufficient to keep the skin temperature at 35°C at the ambient temperature of 5°C. The climatic data of Hong Kong and Shanghai (31°10′0″ N, 121°29′0″ E) in winter are marked as red points and blue points in Fig. 4b and Supplementary Fig. 19 for reference^36,37. Our textile can keep human bodies warm in both places while one wearing black cotton will have the risk of frostbite and hypothermia in Shanghai because the skin temperature is only 22°C. The outstanding solar heating performance of our textile is attributed to the great spectral selectivity and therefore high solar-thermal energy conversion efficiency of Ti₃C₂T_x (η_solar−th = 79.1% under 0.8 sun, T = 55°C, and T₀ = 15°C in real condition of this work).

Warming Performance

As mentioned before, most garment manufacturers only focus on convection suppression but overlook heat loss by thermal radiation of human bodies. For our textile, the low IR emittance of the warming side ($\bar {\varepsilon }=0.22$) can help human bodies reduce thermal radiation to the cold surroundings and outer space. The warming performance of the Janus textile was also investigated in the environment control room without solar irradiation. The required set-points of the ambient temperature for different samples to maintain the skin temperature at 33°C were measured, of which a lower value indicates better warming performance. Besides black cotton, sweater and Mylar blanket were also tested for comparison. It is manifest from Fig. 4c that the set-point of the Janus textile is 4.3 and 2.7°C lower than those of the sweater and the cotton, respectively. In addition, the Janus textile has a thermal insulation performance comparable with the Mylar blanket. To intuitively demonstrate the low emittance of the warming side in our Janus textile, all the samples were attached on a hot plate with a constant temperature of 35°C and characterized by a thermal imager (the default emissivity was set as 0.95 in this work). As shown in Fig. 4d, our textile appears much colder than the cotton and the sweater.

Electric Heating Performance

Solar heating will be less effective at low ambient temperatures and weak solar irradiation. In this condition, the warming side of the Janus textile can still keep the body warm via Joule heating effects because of the excellent electrical conductivity of Ti₃C₂T_x (8000 S cm^− 1 in this work). We can see from Fig. 4e that the skin temperature with our textile can be retained in the thermal comfort zone (33 ± 2°C)³⁸ or slightly higher than 33°C with a safety input below 5 V even at the ambient temperature of 5°C. The heat flux could exceed 66 W m^− 2 during the tests. Such small DC voltage can be easily supplied by dry batteries or mobile power in real applications. Compared with other conductive membrane heaters such as carbon-based coatings, the input power of our textile can be smaller owing to the low emittance of Ti₃C₂T_x MXene, which reduces radiative heat dissipation. As a result, the combination of solar heating and electric heating can protect one from cold injury and hypothermia efficiently most of the time.

Wearability

Besides the thermal performance tests, the wearability of textiles is also of great importance in reality. Firstly, we tested the mechanical properties of our textile. As shown in Fig. 5a, the tensile strength of our textile is around 9.0 MPa, which is as high as that of cotton. Then the folding resistance of the textile was evaluated by a folding test machine. After 10,000 times folding, the absorption/emission spectra of the two sides keep the same as before (Fig. 5b,c). Thirdly, textiles used for clothes should be water vapor permeable for body comfort because sweating happens all the time. Therefore, we also measured the water vapor transmission rate (WVTR) of the Janus textile, as well as cotton and Mylar blanket. As shown in Fig. 5d (data see Supplementary Fig. 20), the WVTR of our textile is 12 mg cm^− 2 h^− 1 and a bit lower than that of cotton (13 mg cm^− 2 h^− 1). Both meet the requirement of the sweat rate of an adult at rest (about 10 mg cm^− 2 h^− 1)³⁹. In contrast, Mylar blanket is almost impermeable to water vapor because of its dense polyester film with a metallic coating. From the concern of safety, textiles with good thermal stability will be more useful. It is reported that Ti₃C₂T_x can keep stable at temperatures as high as 400°C⁴⁰. As for PES, it has a high glass transition temperature of ~ 230°C and a melting point over 400°C (Supplementary Fig. 21). Unlike conventional cotton textiles and PE textiles, PES has outstanding flame retardancy of UL94V-0 (0.46mm)⁴¹, which eliminates the safety risk when one is exposed to fire. In addition, the washability of our textile was also investigated. Raw Ti₃C₂T_x coating is hydrophilic (Supplementary Fig. 22), resulting in poor durability during water washing. In our Janus texitile, we used a simple fluoroalkylsilane (FAS) treatment to make the Ti₃C₂T_x coating hydrophobic with a water contact angle of 145° with negligible change in the spectrum (Supplementary Fig. 8). To demonstrate the washability of our textile, firstly, we placed the textiles coated with hydrophilic Ti₃C₂T_x and hydrophobic Ti₃C₂T_x under water flushing for 1 minute (volumetric flux q = 3.6 m³ s^− 1 m^− 2). The hydrophilic Ti₃C₂T_x coating without treatment faded a little while the hydrophobic Ti₃C₂T_x was quite stable. Further, we immersed our textile with hydrophobic Ti₃C₂T_x in a water tank with water spinning for half an hour. The optical performances of the Janus textile appear unchanged after washing (Fig. 5e,f). Lastly, the UV durability test of the Janus textile was carried out using a UV weathering test machine. The reflectance spectrum remains the same after UV exposure for 2 equivalent months, suggesting the excellent UV resistance of our textile (Supplementary Fig. 23).

In summary, we developed a Janus textile with triple working modes of radiative cooling, solar heating, and electric heating. The textile is fabricated using a scalable two-step process and has a simple Janus structure comprising the cooling layer made of PES-Al₂O₃ fibers and the heating layer made of deposited Ti₃C₂T_x, which are optically coupled. The cooling side of the textile can achieve all-day sub-ambient cooling (0.5–4.7°C) even under harsh operating conditions of high relative humidity (50–80%) and strong solar irradiation. Compared with white cotton, the temperature drop of the simulated skin covered with our textile is around 10.2°C at noon. Regarding the warming side, the combination of solar heating mode and electric heating mode can keep the skin temperature above 33°C for all scenarios at ambient temperatures over 5°C. The low IR emittance of Ti₃C₂T_x significantly reduces the radiation heat loss of human bodies and keeps human bodies warm both indoors and outdoors. Additionally, our textile has cotton-like wearability and great durability to water washing and UV exposure. Overall, given the exceptional thermal regulation performance in all scenarios, wearability, and durability of our textile, it is expected to push the real applications of smart textiles in personal thermal management forward.

Materials. The PES pellets (Ultrason E 6020 P) were purchased from BASF. Dimethylformamide (DMF, AR., 99.8% min., Cat. No. AR1051-G2.5L) was purchased from RCI-Labscan. Colloidal solution of single-layer Ti₃C₂T_x (5 mg ml^− 1 in water) was purchased from Beike 2D materials Co., Ltd.

Fabrication. First, PES pellets (24 wt.%) and Al₂O₃ nanospheres (1.2 wt.%) were dissolved in DMF. The mixture was stirred at 60°C for 24 hours. PES-Al₂O₃ textile was fabricated by electrospinning at the voltages of + 10 kV and − 2 kV with a needle-to-collector distance of 10 cm, a feeding rate of 2 ml h^− 1, and a 22-gauge needle tip. The electrospinning machine (Model TL-Pro-BM, TONG LI TECH, Shenzhen) is equipped with a rotation collector. The hydrophobic surface of the Ti₃C₂T_x layer was processed by fluoroalkylsilane (FAS) modification.⁴² The PFDTMS hydrolysis solution was prepared by mixing 0.5 vol.% acetic acid, 2.0 vol.% PFDTMS, and 97.5 vol.% isopropanol. Then the treated Ti₃C₂T_x was coated on the PES-Al₂O₃ textile by vacuum-assisted filtration method.

Material Characterizations. The morphology was characterized by a scanning electron microscope (JSM-6700F, JEOL).

Optical Measurements. Reflectance and transmittance in the range of 0.3–2.5 µm were measured by a UV/VIS/NIR Spectrometer with a snap-in integrating sphere (Perkin Elmer, Lambda 950). A new spectralon diffuse reflectance standard (Labsphere) was used as the reference. The absorptance was obtained by

$$\alpha \left( \lambda \right)=1 - r\left( \lambda \right) - \tau \left( \lambda \right)$$

Reflectance and transmittance in the range of 2.5–16 µm were measured by a Fourier Transform Infrared Spectrometer (Bruker, Vertex 70) equipped with a golden integrating sphere. The emittance was calculated by

$$\varepsilon \left( \lambda \right)=1 - r\left( \lambda \right) - \tau \left( \lambda \right)$$

where $r\left( \lambda \right)$, $\tau \left( \lambda \right)$, $\alpha \left( \lambda \right)$ and $\varepsilon \left( \lambda \right)$ represent the reflectance, transmittance, absorptance, and emittance at the wavelength $\lambda$. All the measurements were conducted at room temperature.

The solar-thermal energy conversion efficiency can be obtained by^43,44

$${\eta _{solar-th}}\left( T \right)=\bar {\alpha } - \bar {\varepsilon }\frac{{\sigma \left( {{T^4} - T_{0}^{4}} \right)}}{{{I_{solar}}}}$$

Here T and T₀ are the textile temperature and the ambient temperature, respectively, σ is the Stefan-Boltzmann constant, I_solar is the total solar radiation.

A transparent PES film was made by blade coating and vacuum solidification. Then the refractive index of the PES film was measured by an ellipsometer (Alpha-SE, J. A. Woollam Co., Inc).

Thermal Measurements. The heating performance tests were conducted in an environmental control room (DBT and WBT ± 0.1°C) in Hong Kong University of Science and Technology (HKUST). The solar heating performance was evaluated under irradiation of a solar simulator. For the warming performance and electric heating performance tests, the solar simulator was shut down. The input power to the bare skin was ~ 110 W m^− 2 by a source meter. This is determined to keep the bare skin at 33°C at the ambient temperature of 25°C. The input current and voltage were calibrated by a high-precision multimeter (FLUKE 289). Janus textile ($\bar {\varepsilon }=0.22$, thickness = 600 µm), cotton cloth ($\bar {\varepsilon }=0.90$, thickness = 600 µm), sweater ($\bar {\varepsilon }=0.82$, thickness = 300 µm), and Mylar blanket ($\bar {\varepsilon }=0.06$, thickness = 12 µm) were tested..

Mechanical property test

The tensile strength was measured by a universal testing machine (UTM-I2, MTS). The samples were cut to a length of 4 cm. The test speed was kept at 20 mm min^− 1. The folding resistance was tested by MIT folding endurance tester (AISRY INSTRUMENT).

WVTR measurement. The tests are based on ASTM E96 with modification⁴⁵. The WVTR was measured at 35°C and RH of 30 ± 5% in an environmental chamber The sample was placed on a glass bottle (100 ml) filled with 60 ml of deionized water. The bottle was sealed by a silicone gasket and an open-top cap. The total mass of the bottle and the sample was measured every 2 hours. Then The WVTR can be calculated by mass loss divided by time interval and exposed area of the sample.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Vicedo-Cabrera, A. M. et al. Associations of Inter- and Intraday Temperature Change With Mortality. Am. J. Epidemiol. 183, 286–293 (2016).
Hardy, J. D. & Dubois, E. F. Regulation of Heat Loss from the Human Body. Proc. Natl. Acad. Sci. U. S. A. 23, 624–631 (1937).
Kurazumi, Y. et al. Radiative and convective heat transfer coefficients of the human body in natural convection. Build. Sci. 43, 2142–2153 (2008).
Hsu, P. C. et al. Radiative human body cooling by nanoporous polyethylene textile. Science. 353, 1019–1023 (2016).
Peng, Y. C. et al. Nanoporous polyethylene microfibres for large-scale radiative cooling fabric. Nat. Sustain. 1, 105–112 (2018).
Cai, L. et al. Spectrally Selective Nanocomposite Textile for Outdoor Personal Cooling. Adv. Mater. 30, e1802152 (2018).
Cai, L. L. et al. Temperature Regulation in Colored Infrared-Transparent Polyethylene Textiles. Joule. 3, 1478–1486 (2019).
Raman, A. P., Anoma, M. A., Zhu, L., Rephaeli, E. & Fan, S. Passive radiative cooling below ambient air temperature under direct sunlight. Nature. 515, 540–544 (2014).
Zhai, Y. et al. Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling. Science. 355, 1062–1066 (2017).
Mandal, J. et al. Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling. Science. 362, 315–319 (2018).
Li, T. et al. A radiative cooling structural material. Science. 364, 760–763 (2019).
Li, X. et al. Integration of daytime radiative cooling and solar heating for year-round energy saving in buildings. Nat. Commun. 11, 6101 (2020).
Li, D. et al. Scalable and hierarchically designed polymer film as a selective thermal emitter for high-performance all-day radiative cooling. Nat. Nanotechnol. 16, 153–158 (2021).
Wang, T. et al. A structural polymer for highly efficient all-day passive radiative cooling. Nat. Commun. 12, 365 (2021).
Lin, C. et al. A Solution-Processed Inorganic Emitter with High Spectral Selectivity for Efficient Subambient Radiative Cooling in Hot Humid Climates. Adv. Mater. 34, 2109350 (2022).
Zeng, S. et al. Hierarchical-morphology metafabric for scalable passive daytime radiative cooling. Science. 373, 692–696 (2021).
Zhu, B. et al. Subambient daytime radiative cooling textile based on nanoprocessed silk. Nat. Nanotechnol. 16, 1342–1348 (2021).
Hsu, P. C. et al. A dual-mode textile for human body radiative heating and cooling. Sci. adv. 3, e1700895 (2017).
Abebe, M. G., De Corte, A., Rosolen, G. & Maes, B. Janus-Yarn Fabric for Dual-Mode Radiative Heat Management. Phys. Rev. Appl. 16, (2021).
Luo, H. et al. Outdoor Personal Thermal Management with Simultaneous Electricity Generation. Nano Lett. 21, 3879–3886 (2021).
Zhao, D. et al. Radiative sky cooling: Fundamental principles, materials, and applications. Appl. Phys. Rev. 6, 021306 (2019).
Yin, X. B., Yang, R. G., Tan, G. & Fan, S. H. Terrestrial radiative cooling: Using the cold universe as a renewable and sustainable energy source. Science. 370, 786–791 (2020).
Tong, J. K. et al. Infrared-Transparent Visible-Opaque Fabrics for Wearable Personal Thermal Management. Acs Photonics. 2, 769–778 (2015).
Refractive Index of Polymers. Scientific Polymer Products Inc. https://scipoly.com/technical-library/refractive-index-of-polymers-by-index/
Rigby, R. B. Engineering Thermoplastics Ch. 9 (CRC Press, 1985)
Yoon, K., Hsiao, B. S. & Chu, B. Formation of functional polyethersulfone electrospun membrane for water purification by mixed solvent and oxidation processes. Polymer. 50, 2893–2899 (2009).
Zhang, X. et al. Polyethersulfone enwrapped graphene oxide porous particles for water treatment. Chem. Eng. J. 215, 72–81 (2013).
Alenazi, N. A., Hussein, M. A., Alamry, K. A. & Asiri, A. M. Modified polyether-sulfone membrane: A mini review. Des. Monomers Polym. 20, 532–546 (2017).
Lin, J., Ding, B. & Yu, J. Direct fabrication of highly nanoporous polystyrene fibers via electrospinning. ACS Appl. Mater. Interfaces. 2, 521–528 (2010).
Garche, J. et al. Encyclopedia of Electrochemical Power Sources. Newnes: Amsterdam, 2009.
Alenazi, N., Hussein, M., Alamry, K. & Asiri, A. Nanocomposite-Based Aminated Polyethersulfone and Carboxylate Activated Carbon for Environmental Application. A Real Sample Analysis. C. 4, 30 (2018).
Tavangar, T., Hemmati, A., Karimi, M. & Zokaee Ashtiani, F. Layer-by-layer assembly of graphene oxide (GO) on sulfonated polyethersulfone (SPES) substrate for effective dye removal. Polym. Bull. 76, 35–52 (2018).
Jing, W. et al. Scalable and Flexible Electrospun Film for Daytime Subambient Radiative Cooling. ACS Appl. Mater. Interfaces. 29558–29566 (2021).
Wei, W. et al. An Al2O3-cellulose acetate-coated textile for human body cooling. Sol Energ Mat Sol C. 211, (2020).
Pearlmutter, D., Jiao, D. & Garb, Y. The relationship between bioclimatic thermal stress and subjective thermal sensation in pedestrian spaces. Int. J. Biometeorol. 58, 2111–2127 (2014).
Climatological Information Services. Hong Kong Observatory https://www.hko.gov.hk/tc/cis/climat.htm
Share Data. China Meteorological Data Service Centre http://data.cma.cn/
Gagge, A. P., Stolwijk, J. & Hardy, J. Comfort and thermal sensations and associated physiological responses at various ambient temperatures. Environ. Res. 1, 1–20 (1967).
Klous, L., de Ruiter, C., Alkemade, P., Daanen, H. & Gerrett, N. Sweat rate and sweat composition following active or passive heat re-acclimation: A pilot study. Temperature. 8, 90–104 (2020).
Li, Y. et al. 2D Ti3 C2 Tx MXenes: Visible Black but Infrared White Materials. Adv. Mater. e2103054 (2021).
Searle, O. & Pfeiffer, R. Victrex® poly (ethersulfone)(PES) and Victrex® poly (etheretherketone)(PEEK). Polym. Eng. Sci. 25, 474–476 (1985).
Zhao, J. et al. A hydrophobic surface enabled salt-blocking 2D Ti3C2MXene membrane for efficient and stable solar desalination. J. Mater. Chem. A. 6, 16196–16204 (2018).
Weinstein, L. A. et al. Concentrating solar power. Chem. Rev. 115, 12797–12838 (2015).
Li, Y. et al. Solution-Processed All-Ceramic Plasmonic Metamaterials for Efficient Solar-Thermal Conversion over 100–727°C. Adv. Mater. 33, e2005074 (2021).
Cai, L. et al. Warming up human body by nanoporous metallized polyethylene textile. Nat. Commun. 8, 496 (2017).

Acknowledgments

The authors are thankful for the financial support from the Hong Kong General Research Fund (grant nos. 16206020) and Smart Sensors and Environmental Technologies (grant no. IOPCF21EG01) in the Hong Kong University of Science and Technology. This work was also supported in part by the Project of Hetao Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone (HZQB-KCZYB-2020083). K.L. and M.L. contributed equally to this work.

Author contributions

K.L., Y.L. and B.H. designed the research. K.L., M.L. and G.L. performed the fabrication, characterization of the materials. K.L., Y.L., M.L. and C.L. contributed to thermal performance measurements and wearability tests. K.L. and Y.L. performed the simulation. K.L., Y.L. and B.H. analyzed the results and wrote the manuscript. All authors approved the final version of the manuscript.

Competing interests

B.H. and K.L. are the inventors of a US provisional patent currently pending with The Hong Kong University of Science and Technology (No. 63/345,912, filed on 26 May 2022). The remaining authors declare no competing interests.

Additional information

Supplementary Information is available for this paper.

Yes there is potential Competing Interest. B.H. and K.L. are the inventors of a US provisional patent currently pending with The Hong Kong University of Science and Technology (No. 63/345,912, filed on 26 May 2022). The remaining authors declare no competing interests.

Supplementaryinformation.docx

Download PDF

Version 1

posted

You are reading this latest preprint version

A Janus Textile Capable of Radiative Subambient Cooling and Warming for Personal Thermal Management in Harsh Climates

Status:

Version 1

Abstract

Figures

Introduction

Results And Discussion

Optical properties and coupling effects of the Janus textile

Conclusions

Methods

References

Declarations

Additional Declarations

Supplementary Files

Status:

Version 1