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Low temperature daytime radiation cooling textile based on nano fabrication

Time : 2021-11-29 Hits : 17

It takes a lot of energy to adjust the temperature to a comfortable range. Therefore, a great deal of research work is currently devoted to developing passive personal thermal management technologies that can reduce body temperature without any energy expenditure. Although various design methods for cooling textiles have been proposed by previous researchers, textile-based daytime radiation cooling below ambient temperature has not been achieved. A new study shows that the optical properties of silk are due to its layered microstructure, which provides a promising direction for researchers to explore daytime radiation cooling.

Recently, a research team from Nanjing University and Stanford University explored the nanoprocessing of silk through molecular bonding design and extensible coupling agent assisted immersion coating method, and proved that silk nanoprocessing can achieve subenvironmental daytime radiation cooling. Related research was published in Nature Nanotechnology entitled "Subambient Daytime Radiative Cooling textile Based on Nanoprocessed Silk".

Design of nano-silk

The researchers treated the silk with a stretchable coupling agent assisted dip coating, and the silk retained its original wearability. In addition, in order to improve the reflectivity in the ULTRAVIOLET band, inorganic oxide nanoparticles with high refractive index were bonded to silk by molecular bonding strategy using coupling agent. At the same time, the reflectance of visibon-near-infrared band is also improved, and the total reflectance of silk in the whole solar spectrum can reach about 95%.


Design of daytime radiation cooling for nano silk

Preparation and characterization

The Mie scattering theory was used to calculate the scattering efficiency of Al2O3 particles in the UV spectrum as a function of particle size, and Al2O3 nanoparticles with a size of about 300 nm were determined to be used for subsequent experiments. Tetrabutyl titanate was selected as coupling agent and Al2O3 particles were attached to silk. It is found that tetrabutyl titanate can form hydrogen bond with the hydroxyl group on Al2O3 surface and reduce the agglomeration of Al2O3 particles. In addition, tetrabutyl titanate can form strong covalent bonds with amino acids in silk. Therefore, strong adhesion between Al2O3 particles and silk is formed through this molecular bond design strategy.


Preparation and characterization of nano-silk

The performance test

The researchers tested natural and nanosilk silk under continuous radiation cooling for 22 hours. The study found that due to heat release, the temperature of natural silk is lower than the ambient temperature at night, but in the daytime (9:00 ~17:00) its temperature is usually higher than the ambient temperature. In contrast, the temperature of the nanosilk was consistently lower than the ambient temperature both during the day and at night, and the average temperature of the nanosilk was still about 3.5 °C lower than the ambient air temperature at 15:00 when the solar irradiance exceeded 800 W·m-2.


Radiation cooling performance test of natural silk and nano silk

The researchers also tested the cooling properties of silk covering simulated skin in sunlight. The simulated skin consists of a silicone rubber insulated flexible heater. The results showed that when the simulated skin was covered with nano-silk, the skin temperature was about 8 ℃ and 12.5 ℃ lower than that of the simulated skin covered with natural silk or cotton, respectively. The above results show that the nanosilk has excellent cooling properties due to the combination of its enhanced solar reflection and its inherent thermal radiation properties, which minimize the heat input, and these properties are not affected by the nanotreatment.

The researchers also tested how comfortable the silk was to wear. The results showed that the water vapor permeability of nano-silk was similar to that of natural silk and Tyvek, but slightly higher than that of cotton. Under the cover of Al2O3 nanoparticles, the core suction distance of silk is still 10 mm, comparable to natural silk; The washability of the silk fabric was tested by washing and sun drying.


Thermal and wearability test of nano silk

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