Plasma is a collection of charged particles and neutral particles, which is the fourth form of matter in nature besides solids, liquids, and gases. There are a large number of free electrons and ions in plasma, which appear neutral as a whole. The movement of electrons inside is very active and complex, and particles constantly collide and ionize with each other during motion, producing more electron ion pairs. In addition, plasma has compressibility, and under external pressure or electromagnetic force, the density of plasma will undergo significant changes, which allows people to apply different functions of plasma by controlling pressure or electromagnetic force. Plasma can be divided into two types based on temperature: high-temperature plasma and low-temperature plasma. High temperature plasma can generally reach a temperature of 10 ⁴ -10 ⁷ K and has extremely high internal capabilities. It is generally used for research on nuclear fusion reactions and synthesis of high-temperature materials; The temperature of low-temperature plasma is close to room temperature and can be easily controlled, with atmospheric plasma being plasma generated at atmospheric pressure. There is no complex vacuum system constraint in atmospheric plasma, and the gas pressure is close to atmospheric pressure. Compared with low-pressure plasma material surface treatment technology, it has the advantages of simple structure, low operating cost, and stability.

The main types of atmospheric plasma systems

Atmospheric plasma (APP) processing equipment can be divided into dielectric barrier discharge (DBD), radio frequency discharge (RF Discharge), microwave discharge (MW Discharge), arc discharge, corona discharge and other methods based on the discharge mechanism.

Method of surface modification of materials by atmospheric plasma

The treatment of material surfaces by atmospheric plasma can be used to improve the physical and chemical properties of materials, such as modifying the surface of polymer materials, introducing polar groups (such as carboxyl, hydroxyl, etc.) into plastics, rubber, and other materials, enhancing the interfacial compatibility between these materials and inks or adhesives, and is suitable for the packaging materials industry. Plasma can also form etching on the surface of materials through the impact of a large number of high-speed particles, improving the roughness of the material surface. For example, after plasma treatment on ceramic or metal surfaces, it can enhance the adhesion of subsequent coatings and extend their service life. In addition, plasma also has a certain cleaning effect on the surface of materials. For example, in the semiconductor manufacturing industry, plasma treatment can be used to clean the wafer surface, remove residual photoresist, metal impurities and other substances on the wafer surface, and improve the yield of wafers. Therefore, the methods of plasma surface modification of materials can be summarized as follows:

(1) Surface etching and roughening

By bombarding the material surface with a large number of high-energy particles inside the plasma, etching is formed on the material surface, increasing its roughness and specific surface area.

(2) Surface cross-linking reinforcement

The impact of high-energy particles causes the molecular chains on the surface of the material to break, generating free radicals that recombine to form a dense cross-linked layer.

(3) The generation of free radicals and the introduction of functional groups

Active particles (such as O and N radicals) in plasma react with material surfaces, breaking inert chemical bonds such as C-F and C-C, and generating new polar groups (such as - COOH, - OH, - NH ₂).