Industry | New porous polymer coating with adjustable light and heat control

Researchers from the Columbia Engineering Research Institute have developed a porous polymer coating (PPC) that has optical switchability to solar wavelengths to adjust the absorption and reflection of sunlight, which helps buildings Regulation of light and heat.
Dr.
Mandal in the research team accidentally noticed that when a few drops of alcohol splashed on the white fluoropolymer PPC coating, it became transparent.
From this accidental discovery, the team started a study on the optical transformation mechanism of the PPC coating.
research work.
Mandal believes that "this mechanism is similar to the mechanism that paper becomes transparent when it is damp.
It has also been studied before, but the more drastic change has made us interested in studying it and wanting to know its application value.
"light shade and adjust the indoor temperature to adjust the indoor temperature and light brightness adjust the indoor temperature and light shade Dr.
Mandal said, "our results indicate that, by the other common liquids such as alcohol or water-wet coating PPC, sunlight and so on The heat radiation wavelength range has the ability to reversibly change the light transmittance.
This coating is applied to the surface of the plastic plate or glass plate, so that the building has the function of adjusting the indoor temperature and the brightness of the light.
" The design style of the research team Similar to smart windows, but with higher optical switchability, and the materials used are lower in cost and simpler, which is convenient for large-scale development.
The previous design idea was based on the fluoropolymer coating having a micro-nano-scale microporous structure, which can play a role in cooling buildings, but the cooling function of the coating is static.
For places like New York, the summer is hot and the winter is cold.
, The earlier design ideas should be upgraded to a dynamic mode that enables the coating to switch between hot and cold, so as to have more practical application significance.
Porous materials like paper have a white appearance because the air in the micropores and the porous material have a different refractive index.
After being wetted by water, the refractive index of water is closer to that of the porous material, the scattered light is reduced and the light transmission is increased, thus gradually becoming transparent.
As the refractive index gets closer, the light transmittance is higher.
The researchers found that the refractive index of fluoropolymer and alcohol are very close.
The head of the laboratory, Dr.
Yang, said, “When the porous polymer is wetted, the optical performance is similar.
At this time, the light is no longer scattered, but passes through the polymer like a solid glass, making the porous polymer transparent.
”PPC coating can adjust the amount of sunlight in buildings PPC coating can adjust the amount of sunlight in buildings PPC coating can adjust the amountofsunlight in buildingsBecause the refractive index of alcohol and fluoropolymer are very matched, the team changed the solar transmittance of PPC coating The amplitude reached about 74%.
In the visible light range, the variation range can reach about 80%.
Although the speed of change is slower than that of typical smart windows, the change in transmittance is much higher, which makes PPC coatings attractive in regulating the sunlight in buildings.
The researchers also studied how to apply the light-switching function of the coating to temperature regulation.
Dr.
Yang said: “In the summer, the white roof can keep the building cool, but in the winter, it becomes black, which facilitates the absorption of heat energy and raises the temperature of the building, thereby significantly reducing the building’s air-conditioning and heating costs.
” Performance test Performance testTo verify their design, the researchers placed a test board coated with a PPC coating on a simulated house with a black roof.
One of the test panels is dry and reflective, while the other test panel is wet and transparent, with a black roof underneath the test panel.
In the summer noon sun, the white roof is 3? cooler than the surrounding air temperature? Around C, and the black roof is much hotter.
The study pointed out that the PPC-coated roof has the function of switching between reflection and transmission, which can be used to adjust the indoor temperature of the building.
 Switch between "Igloo" state and "Greenhouse" mode Switch between "Igloo" state and "Greenhouse" mode Switch between "Igloo" state and "Greenhouse" mode Theresearch team also studied thermal infrared wavelengths Through the research of porous polyethylene polymer coating with infrared-transparency change function, a new cold-heat conversion mode has been discovered.
After the porous polyethylene polymer coating is dried, it will reflect sunlight, but will transmit radiant heat, similar to an "ice house".
Wetting the polymer coating to make it transmit sunlight, and the liquid in it can absorb thermal radiation and inhibit the transmission of thermal energy, similar to a "greenhouse".
Since this coating can regulate both sunlight and heat radiation, it can regulate heat energy all-weather.
Other potential application research Other potential application research Other potential application researchteam has alsoconductedresearch on other potential applicationsof coatings, such as thermally induced camouflage coatings, climate-responsive coatings, etc.
The latter is suitable for buildings in Mediterranean climate regions and coastal areas of California.
These regions are dry in summer and rainy in winter, and climate-responsive coatings help to insulate or keep buildings warm.