Shanghai Jiaotong University develops a new type of flexible film
xinstJul 09, 2020
With the development of science and technology, the membrane material biomimetic film industry is also making continuous progress. More and more new functional membranes are constantly appearing, which brings more convenience to our lives. Recently, Shanghai Jiaotong University has developed a new type of flexible film. Here, Xinst will show you what kind of changes this film can bring to people’s lives!
Summer is hot, the most comfortable thing for people is to eat iced watermelon in the air-conditioned room. Whether it is a cool room or a chilled watermelon, refrigeration technology is required. Most existing refrigeration technologies are based on vapor compression refrigeration, which requires the use of refrigerants with potential environmental pollution on the one hand and the consumption of large amounts of electricity on the other.
According to statistics, China’s building energy consumption accounts for about 35% of the country’s total energy consumption, and the cooling and air conditioning system’s energy consumption accounts for about 50 to 60% of the building’s energy consumption. Therefore, refrigeration technology has become a major energy consumer, and the technology needs to be updated. . In nature, some organisms have a special surface structure, and through passive radiation, show amazing thermal regulation ability. It is undoubtedly a promising technology to learn nature, prepare special surface structures, and realize passive radiation cooling.
A few days ago, the team of Professor Zhou Han and Professor Fan Tongxiang of Shanghai Jiaotong University and their collaborators discovered that the multi-level micro-nano structure of the long horn beetle (Neocerambyx Gigas) wings shows excellent temperature regulation ability, and then based on the new photomask Method, bionic preparation of a flexible film with a similar structure to achieve passive radiation cooling, at the same time, this technology also realizes the macro preparation of radiation cooling film. Related work was published in “PNAS” as “Biologically inspired flexible photonic films for efficient passive radiative cooling”.
Morphology and thermal regulation mechanism of the long-wing beetle
A long-horned beetle lives in volcanic areas in Indonesia and Thailand. The temperature where it lives usually rises to above 40°C (104°F) in summer, and the ground temperature can reach 70°C (158°F). These long-horned beetles have attracted much attention from researchers due to their ability to resist heat and regulate heat.
The researchers first observed the microstructure of the long wing beetle’s front wing, and found that the surface of the front wing was covered with fluff, with a density of more than 25,500 per square centimeter. The color of the front wing can also effectively resist the fading treatment, showing the structural color characteristics of the photonic crystal. Further observation revealed that each fluff is a triangular structure composed of two smooth surfaces and a rough surface. The rough surface is a corrugated structure with a width of 1 μm and a height of 0.18 μm, which together with the fluff itself constitutes a multi-level rough structure.
The optical properties and temperature adjustment capabilities of the long-horn beetle’s front wing (a) the reflection of the front wing in the visible-near infrared spectral range; (b) the change in the reflectance of the front wing under different ethanol conditions; (cd) the visible-near infrared light Enter the reflection from different directions of the fluff; (e) the ratio of the absorption and reflected light ratio of the front wing in the mid-infrared region with the wavelength; (f) the change of the reflectance of the fluff at different incident angles; (gh) the front wing in vacuum and air The surface temperature changes with (red) and without (black) fluff.
After grasping the microstructure of the surface of the front wing, the researchers studied the optical properties and temperature adjustment capabilities. First of all, the researchers studied the reflection of the front wings with or without fluff, and found that the presence of fluff can increase the light reflectance by more than 35%, and through the immersion experiment of ethanol solution, it was further determined that high reflectance is a benefit Multi-level microstructure existing on the surface. In order to further explore the mechanism principle, the researchers used time-domain finite difference simulation to study the optical characteristics of multi-level microstructures at different incident angles. The optics entering from a side of the triangular corrugated surface with a small incident angle will undergo total internal reflection. At the same time, when the wavelength of the incident light is similar to the ripple width, it will generate strong Mie scattering, so that it has a strong reflectivity at all incident angles. The absorption/emission rate on the surface of the front wing covered with fluff reaches 0.94, which indicates that the beetle dissipates the body’s heat well. The time-temperature curve also shows that in the presence of surface fluff, a significant cooling effect can reach 3.2 ℃ and 1.5 ℃ temperature drops in vacuum and air, respectively. This excellent temperature control ability is beneficial for insects to carry out daily foraging activities in high temperature and sun exposure environments.
Preparation and Characterization of Bionic Film
Based on the study of the surface structure and temperature control ability of the long-horn beetle, the researchers tried to bionic prepare a bionic radiation cooling film with a similar structure and achieve radiation cooling control.
Preparation and morphological characteristics of bionic films biomimetic film. (A) Preparation process of template and bionic film; (bc) Scanning electron microscope photos of silicon template and film; (d) Macro photo of bionic film; (e) Schematic diagram of cooling principle of bionic film; (f) Cross-section scan of bionic film Electron microscope photo.
In the preparation process, firstly, a silicon template with a triangular structure is prepared by photolithography, and then a precursor solution containing silicone and alumina microspheres is spin-coated on the surface of the template. After thermal polymerization, the surface is separated into a triangular structure. Structured film. This method can achieve large-scale, large-scale preparation of the film, and has certain versatility. It can achieve the doping of various ceramic particles such as zinc oxide, zirconium oxide, magnesium oxide, and titanium dioxide.
The optical properties of the bionic biomimetic film film and its radiation cooling ability. (A) Radiation efficiency of bionic film (black) and smooth film (red); (b) Ratio of simulated average absorption rate and emissivity in TASW; (c) Diagram of measurement device for radiation heat dissipation performance; (d) Bionic film and Air temperature; (e) Temperature drop caused by the bionic film; (fh) Sunlight intensity (f), relative humidity (g), and heat dissipation power (h) during the measurement process with time.
After obtaining the biomimetic film, the researchers tested its performance, and the results showed that its average reflectivity in the solar spectral range was about 95%, and the average emissivity in TASW was> 0.96, which is compared to the emissivity of the smooth film Has been greatly improved. Then the actual cooling capacity of the film was evaluated. Under the conditions of an average solar intensity of about 862 W·m-2 and a humidity of 22.7%, the average temperature of the bionic film dropped to 5.1 °C and the maximum temperature dropped to 7 ° C. The results show that the biomimetic film can not only cool itself, but also significantly reduce the temperature of the surrounding environment and the equipment or heating body covered by the film.
The biomimetic film can not only achieve radiant cooling but also other functions at the same time. For example, due to the low surface energy of silicone rubber combined with the micro-nano-level rough surface of the film, the film also has the ability of super-hydrophobic and self-cleaning. Researchers have also applied this kind of bionic radiation cooling film to wearable devices, personal electronic devices, automobiles and other devices, which have shown good cooling effects.
The researchers explored the principle of temperature control by studying the microstructure of the long-horned beetle; then based on this principle, a flexible bionic film was prepared to achieve passive radiation cooling with an average temperature drop of more than 5 ℃; at the same time, this bionic The flexibility and hydrophobicity of the film also laid the foundation for its application in various wearable devices, electronic devices, and vehicles. This passive radiation cooling thermal regulation technology is undoubtedly more energy-saving and environmentally friendly. This work also paved the way for the subsequent mass production of radiation cooling technology based on high-performance photon radiators.