Nanomaterials' properties

Nanomaterials refer to ultrafine materials with a grain size of nanometer level (1 m). Their sizes are between molecules, atoms and bulk materials. They generally refer to tiny solid powders in the range of 1 ~ 100nm. Nanomaterial is a kind of third kind of solid material which is different from both crystalline and amorphous state. It is defined by the size of the structural units of nanomaterial: grains, non-grains, separated ultrafine particles, etc. At present, the international will be in the SCOPE of L ~ lOOnm ultra-fine particles and their compact aggregates, as well as the materials composed of nanocrystals, collectively referred to as nanomaterials, including metal, non-metal, organic, inorganic and biological powder materials.  

Properties of nanomaterials  

1. Surface effect. The surface effect of nanomaterials refers to the change in properties caused by the sharp increase of the ratio of the surface atomic number to the total atomic number of the nanoparticles with the decrease of the particle size. The surface area of a spherical particle is proportional to the square of its diameter, and its volume is proportional to the square of its diameter, so its specific surface area (surface area/volume) is inversely proportional to its diameter. As the particle diameter decreases, the specific surface area will increase significantly. For example, when the particle size is 10nm, the specific surface area is 90M2G-1;  When the particle size was 5nm, the specific surface area was 180M2G-1. The specific surface area increased to 450m2G-1 when the particle size decreased to 2nm.  When the particle diameter decreases to nanometer scale, not only the number of surface atoms increases rapidly, but also the surface area and surface energy of the nanoparticles increase rapidly.  

2. Size effect. The change of macroscopic physical properties caused by the decrease of particle size is called small size effect. For ultrafine particles, the size decreases and the specific surface area increases significantly, resulting in special optical properties, thermal properties, magnetic properties and mechanical properties. The small size effect of ultrafine particles is also shown in superconductivity, dielectric properties, acoustic properties and chemical properties.  

3. Volume effect. Due to the small size of nanoparticles, the number of atoms contained is very small. Therefore, many phenomena, such as adsorption, catalysis, diffusion, sintering and other physical and chemical properties related to the interface state, will be significantly different from the properties of large-particle traditional materials and cannot be explained by the properties of massive materials, which usually have infinite atoms. This special phenomenon is usually called volume effect.  

4. Quantum size effect. This effect refers to the electron energy level near Fermi level changes from quasi-continuous energy level to discrete energy level when particle size drops to a certain value. The fluctuation of electrons in discrete quantized energy levels in nanomaterials gives nanomaterials a series of special properties, such as specific catalysis, strong oxidation and reduction.  

5. Quantum tunneling. The ability of microscopic particles to penetrate a barrier is called tunneling. The magnetization of nanoparticles also has tunneling effect, which can change through the barrier of macroscopic system, which is called macroscopic quantum tunneling effect of nanoparticles. Its research is of great significance to basic research and practical application, such as conductive and magnetic polymers and microwave absorbing polymers.