1 and 20 14 Threadsmiths, a clothing technology company in Melbourne, invented a super-hydrophobic T-shirt imitating lotus leaves. This kind of T-shirt can be washed for more than 80 times, and it keeps super-hydrophobic performance. They used nanotechnology to reweave cotton fibers to make them waterproof.
2. The Turkish-German joint research team used filter paper as porous substrate, and modified PDMS)/ inorganic micro-nano particles (particle size ranging from several nanometers to several tens of microns) on one side to construct Janus paper with significant difference in wettability between superhydrophobic and hydrophilic.
The paper has excellent chemical stability, mechanical stability and flexibility, while maintaining good air permeability, and has great application prospects in wound treatment.
From the static contact angle of solid surface, the key to determine the hydrophobicity of solid surface lies in the chemical composition of material surface, and the roughness of surface only enhances this effect. Therefore, when constructing a superhydrophobic solid surface, a rough surface is usually constructed on a surface with low surface energy, or a substance with low surface energy is modified on the rough surface.
At first, people began to study the preparation of low surface energy substances, and found that the solid materials with the lowest surface energy at present are siloxane and fluorine-containing materials. Among them, fluorine-containing material is the best, its surface energy is about 10 mN/m lower than that of siloxane, and fluorine is the element with the smallest atomic radius except hydrogen.
It has strong electronegativity, high fluorocarbon bond energy, low cohesive energy, high heat and chemical stability. It has the characteristics of heat resistance, weather resistance, excellent chemical medium resistance and low refractive index. When the -—CF3 groups on the surface of the material are stacked in a hexagonal compact and orderly arrangement, the surface tension of the solid surface is the lowest, which is 6.7 mJ/m2. Therefore, most materials with low surface energy are mainly fluorine-containing materials.
In addition, people began to try to prepare superhydrophobic coatings by controlling the surface structure in different ways. At present, the commonly used methods include layer-by-layer self-assembly, physical or chemical vapor deposition, etching, template method, electrostatic spraying and sol-gel method.
Extended data
Super-hydrophobicity is a special wettability, which generally means that water drops are spherical on the solid surface, the contact angle is greater than 150 degrees, and the rolling angle is less than 10 degrees.
The lower the surface energy of the material (the energy of molecules on the surface of the material is greater than that of internal molecules), the better the hydrophobicity. When the material with low surface energy has a slightly rough structure, an air film will be formed between the water droplets and the material to prevent water from wetting the surface of the material, thus forming a super-hydrophobic state.
Superhydrophobic surface was originally inspired by the "lotus leaf effect". In the 1990s, Barthlott, a botanist from Bonn University, Germany, revealed the surface structure of lotus leaves and found that the "self-cleaning" of lotus leaves originated from its micro-nano structure.
There are micron-sized papillae on the surface of lotus leaf, and there are nano-sized wax crystals on the papillae. This micro-nano rough structure can greatly improve the contact angle of water droplets on it, resulting in water droplets rolling down easily.
Because water droplets can take away pollutants when rolling on the surface of superhydrophobic materials, the surface of materials can be kept clean. Therefore, superhydrophobic materials have multiple characteristics such as waterproof, anti-corrosion, anti-icing and anti-adhesion.
The surface of lotus leaf not only has superhydrophobic property-"lotus leaf effect", but also shows the wettability of lotus leaf with superhydrophobic surface and hydrophilic bottom. At present, there is relatively little research on constructing Janus membrane with significant wettability difference by simulating this characteristic of lotus leaf surface.
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