In the study of surface modification of polymer films, plasma treatment is considered to be the most promising surface modification method. In recent years, plasma technology has been widely used in the surface modification of polymer materials. Compared with some other modification methods, plasma modification only modifies the shallow surface ( < 10-8m ) of the material, does not damage the internal structure of the material, and has little effect on the overall performance of the material, especially the mechanical properties. However, it can significantly improve the polarity and structure of the material surface, thereby improving the wettability of the material. When the material is modified by plasma, first of all, the particles emitted by the plasma interact with the surface of the polymer material, causing free radical reaction ; after that, free radicals undergo a series of chemical reactions, such as conversion, cracking, oxidation, disproportionation and coupling, so as to achieve the purpose of enhancing the surface functionality of polymer materials. Among them, the active particles that initiate the free radical reaction are mainly produced by the collision of high-speed moving electrons in the plasma with gas molecules. Researchers have found that a variety of active particles exist in low temperature plasma, and these active particles can be divided into six categories, namely electrons, photons, molecules in the ground state energy level ( atoms or free radicals ), stimulated atoms or molecular positive ions ( molecules or atoms ), negative ions ( atoms or molecules ).

The principle of low temperature plasma modification of polymer film

The bond energy of common chemical bonds in organic matter is lower than that of active particles in plasma, so it is easy to produce chemical reaction on the surface of polymer when plasma acts on the surface of polymer. When these active particles are in contact with macromolecular substances, energy exchange occurs, and the chemical bonds of macromolecules are opened. If the reaction medium of low temperature plasma is oxygen, hydrogen and ammonia, these gases will react with polymer substances to form polar groups containing oxygen, hydrogen and nitrogen. If the reaction medium of the plasma is inert gas argon or nitrogen, free radicals or dense cross-linked structures formed by unsaturated chemical bonds will be generated on the surface of the polymer, which will improve the structure and hydrophilicity of the surface of the material. The other properties of the film are also improved, so that the overall performance of the substrate is improved.

Advantages of low temperature plasma treatment of polymer films

For the modification of polymer films, low temperature plasma modification is generally used. The modification of polymer materials by low temperature plasma has the following advantages : 1 For the reaction with high activation energy but slow reaction rate and possible thermodynamic reaction, the activation energy can be reduced and the reaction rate can be increased by low temperature plasma modification ; 2 For some reactions that need to be carried out at high temperature, the modification of materials can be realized by low temperature plasma modification, ionization or dissociation of molecules to form new groups. 3 The depth of action on the surface of the polymer can be from tens to hundreds of nanometers, but at the same time, the mechanical properties of the matrix can be maintained without damaging the material matrix, while changing the surface energy of the material, improving the hydrophilicity of the material surface, improving the surface morphology, and generating functional groups. 4. The process is simple, easy to control, water saving, energy saving, cost reduction, no pollution to the environment.