Temperature Change of Superelastic Anti-fatigue Carbon Nanofiber Aerogel

[ Instrument Network Instrument R & D ] Lightweight compressible materials with superelasticity and fatigue resistance, especially materials which can adapt to a wide temperature range, are ideal materials in the fields of aerospace, mechanical buffering, energy damping and soft robots. Many low-density polymer foams are highly compressible, but they tend to fatigue when reused, and undergo superelastic degradation near the polymer's glass transition and melting temperature.

A polymer is defined as a long chain formed by joining many smaller molecules, called a monomer. Although paper chains present simple images of polymers, in practical applications, polymers have more uses. They form an integral part of many items used in daily life: plastic containers, nylon products, rubber tires and more.

Although researchers have developed a variety of thermally stable lightweight metal and ceramic foam materials, they generally have minimal reversible compressibility and exhibit fatigue under cyclic deformation. Carbon nanotubes and graphene have been used as basic materials for preparing lightweight superelastic materials in recent years because of their inherent superelasticity and thermomechanical stability. Although the excellent properties of such materials have been reported in related literature, the complex equipment and preparation processes involved in these works make it possible to produce materials with only millimeter size. On the other hand, complex hierarchical biological materials that have evolved from hundreds of millions of years in nature have attracted much attention due to their excellent mechanical properties. However, because they are pure organic or organic / inorganic composite structures, they are usually only suitable for very narrow temperatures. Working within range. Therefore, transforming these non-thermally stable structural biomaterials into thermally stable graphite materials with inherent hierarchical structure is expected to create thermodynamically stable materials.

Carbon nanotubes, as one-dimensional nanomaterials, are lightweight and have a hexagonal structure with perfect connections. They have many unusual mechanical, electrical, and chemical properties. In recent years, with the deepening of the research on carbon nanotubes and nanomaterials, its broad application prospects have been continuously shown.

Carbon nanotubes, also known as bucky tubes, are one-dimensional quantum materials with special structures (radial dimensions are on the order of nanometers, axial dimensions are on the order of micrometers, and both ends of the tube are basically sealed). Carbon nanotubes are mainly coaxial tubes composed of carbon atoms arranged in hexagons, ranging from several layers to tens of layers. A fixed distance is maintained between the layers, about 0.34 nm, and the diameter is generally 2-20 nm. And according to the different orientation of the carbon hexagon in the axial direction, it can be divided into three types: zigzag, armchair and spiral. The spiral carbon nanotubes have chirality, while the zigzag and armchair carbon nanotubes have no chirality.

Recently, Yu Shuhong's team and Liang Haiwei's group at the University of Science and Technology of China reported a method for thermally transforming structural biomaterials (BC, bacterial cellulose) into graphitic carbon nanofiber aerogels (CNFAs) through pyrolysis chemistry control. The prepared carbon aerogel perfectly inherits the macro-to-micro hierarchical structure of bacterial cellulose, and has significant thermomechanical properties. In particular, it can maintain superelasticity without plastic deformation after 2 × 106 compression cycles, and has excellent superelasticity and fatigue resistance that do not change with temperature in a wide range of temperatures of at least -100 to 500 ° C. This aerogel has unique advantages over polymer foam, metal foam, and ceramic foam in terms of thermomechanical stability and fatigue resistance, realizes large-scale synthesis, and has the economic advantages of biological materials.

According to reports, the "carbon sponge" has high elasticity and can be restored to its original state after being compressed by 80%. It has super fast and super high adsorption force for organic solvents, and it has been reported as an oil absorption material so far. Existing oil-absorbing products generally can only suck about 10 times its own mass of liquid, while the "carbon sponge" absorbs about 250 times, up to 900 times, and only absorbs oil without absorbing water. "Big Stomach King" eats organic matter very fast: each "gram of carbon sponge" can absorb 68.8 grams of organic matter per second. This makes people think of using it to deal with oil spills at sea. "You can sprinkle them on the sea surface, and you can quickly absorb the oil spills. Because of the elasticity, the absorbed oil can be pressed out for recycling." Carbon sponge " It can also be reused, "said the researchers.

The team developed a method for pyrolyzing chemical regulation of bacterial cellulose (BC) using inorganic salts, realizing a large-scale synthesis and morphological retention of a new carbonization process. The developed carbon nanofiber aerogel inherited bacteria well. The hierarchical structure of cellulose from macro to micro shows obvious superelasticity and anti-fatigue performance that does not change with temperature in a wide temperature range.

Bacterial cellulose has the same molecular structural unit as natural cellulose produced by plants or seaweeds, but bacterial cellulose fibers have many unique properties.

â‘ Compared with plant cellulose, bacterial cellulose has no by-products such as lignin, pectin, and hemicellulose, and has high crystallinity (up to 95%, plant cellulose is 65%) and high degree of polymerization (DP (Value 2 000-8 000);

â‘¡ Super fine mesh structure. Bacterial cellulose fibers are composed of microfibers with a diameter of 3 to 4 nanometers into 40 to 60 nanometer thick fiber bundles, and are intertwined to form a developed ultra-fine network structure;

â‘¢ The elastic modulus of bacterial cellulose is several times to ten times that of general plant fibers, and the tensile strength is high;

④ Bacterial cellulose has strong water retention values ​​(WRV). Unwrapped bacterial cellulose has a WRV value of more than 1000%, and the water holding capacity after freeze-drying still exceeds 600%. The swellability of bacterial cellulose after drying at 100 ℃ is equivalent to that of cotton linter;

⑤ Bacterial cellulose has high biocompatibility, adaptability and good biodegradability;

â‘¥ Adjustability during bacterial cellulose biosynthesis.

Because carbon nanofiber aerogels have excellent thermally stable mechanical properties and can be macroscopically prepared, they will have important application prospects in many fields, especially suitable for mechanical buffering, pressure sensing, energy damping and aerospace solar energy under extreme conditions. Battery, etc.

Source: University of Science and Technology of China, Encyclopedia