Nanomaterials exhibit many exotic properties that traditional materials do not have. The first thing we need to know is that the nanometer (mainly refers to less than 100nm) of the composition of nanomaterials has four major effects:

1. Small size effect

The boundary conditions of the crystal periodicity are destroyed; the atomic density near the surface layer of the amorphous nanoparticle decreases, resulting in changes in the characteristics of sound, light, electricity, magnetism, and heat.

With the quantitative change of particle size, the qualitative change of particle properties will be caused under certain conditions. The change in macroscopic physical properties due to particle size reduction is called the small size effect. For nanoparticles, the size becomes smaller, and the specific surface area also increases significantly, so that the magnetic properties, internal pressure, light absorption, thermal resistance, chemical activity, catalysis and melting point have undergone great changes compared with ordinary particles, resulting in a The novel nature of the series. For example, the absorption of light by nano metal powders increases significantly, and the plasmon resonance frequency shift of the absorption peak occurs; the magnetic properties of small-sized nanoparticles are obviously different from those of bulk materials, from magnetic ordered state to magnetic disordered state, and the superconducting phase is normal. phase transformation. Compared with large-sized solid substances, the melting point of nanoparticles will decrease significantly. For example, the melting point of 2nm gold particles is 600K, and the melting point rises rapidly with the increase of particle size, and the bulk gold is 1337K.

2. Surface effect

The particle size of nanoparticles is small, the number of surface atoms increases, the surface area and surface tension become larger, and the coordination of atoms is insufficient, so that the nanoparticles have high chemical activity.

The surface area of spherical particles is proportional to the square of the diameter, and its volume is proportional to the cube of the diameter, so its specific surface area (surface area/volume) is inversely proportional to the diameter. The specific surface area increases significantly as the particle diameter decreases. For example, when the particle size is 10nm, the specific surface area is 90m2/g; when the particle size is 5nm, the specific surface area is 180m2/g; when the particle size drops to 2nm, the specific surface area increases sharply to 450m2/g. The reduction of particle diameter to nanometer level not only causes a rapid increase in the number of surface atoms, but also increases the surface area and surface energy of nanoparticles. This is mainly because the number of atoms on the surface is large, and the crystal field environment and binding energy of the surface atoms are different from those of the internal atoms. The surface atoms lack adjacent atoms, have many dangling bonds, have unsaturated properties, and are easy to combine with other atoms to stabilize, so they have great chemical activity. Its surface energy is greatly increased. This activity of surface atoms not only causes changes in atomic transport and configuration on the surface of nanoparticles, but also changes in surface electron spin conformation and electron energy spectrum.

3. Quantum size effect

When the particle size decreases to a certain value, the electron energy levels near the Fermi level change from quasi-continuous to discrete levels. The splitting of the energy level spacing will inevitably lead to significant differences in the macroscopic properties of nanoparticles.

The energy bands of bulk materials can be seen as continuous, while the energy bands of nanomaterials between atoms and bulk materials will be split into discrete energy levels. The spacing between energy levels increases with decreasing particle size. When thermal energy, electric field energy, or magnetic field energy is smaller than the average energy level spacing, a series of anomalous properties that are completely different from macroscopic objects will appear, which are called quantum effects. This effect can make the nanoparticles have high optical nonlinearity, specific catalytic and photocatalytic properties.

4. Macroscopic quantum tunneling effect

Microscopic particles have the ability to penetrate the potential barrier, known as tunneling. Studies have found that macroscopic physical quantities such as microparticle magnetization and magnetic flux in quantum coherent devices also have tunneling effects. In addition, nanomaterials have synergistic effects and quantum coupling effects caused by combination, and many exotic properties of nanomaterials can be controlled by external fields.