In nature, matter mostly exists in solid, liquid, gas, and three states, but in the universe, the majority of matter exists in the form of plasma. These forms of matter can undergo transformation, and providing energy to solid matter can increase the spacing between particles, allowing it to transform into a liquid state. When energy is continuously supplied, liquid substances will transform into gas. If sufficient electrical energy is applied to a gaseous substance, the electrons outside the gas molecule nucleus are converted into free electrons under the action of an electric field and excited by the electric field. These free electrons move, collide with the molecules and atoms of the gaseous substance, and ionize, producing active particles such as ions and electrons. This mixture of positively and negatively charged particles is called plasma.

Low temperature plasma can be used for surface modification of various materials under normal pressure or vacuum conditions, and the reaction conditions for surface modification of materials by low-temperature plasma are relatively mild, without the generation of harmful gases. Currently, good research progress has been made in this field.

The principle of low-temperature plasma surface modification

Low temperature plasma surface modification technology utilizes active particles such as electrons, ions, and neutral particles with a certain energy distribution contained in the plasma generated by gas discharge to interact with the material surface, transferring their own energy to the molecules and atoms on the material surface. Due to the energy contained in the plasma being much greater than the binding energy of the material molecules, the molecular bonds on the material surface break and recombine with the polar groups carried in the plasma, introducing different active groups to obtain the desired surface properties. Under the action of these reaction processes, the surface morphology, physical and chemical morphology of the material may change, endowing the treated material with unique functionality. The main goal is usually to introduce hydrophilic functional groups such as oxygen and nitrogen on the surface of the material, thereby enhancing its surface properties, including wetting and biocompatibility. At the same time, high-speed particles also have a good cleaning effect on the surface of materials.

Low temperature plasma surface modification technology has significant advantages such as low temperature, high chemical activity, good controllability, simple surface treatment operation, low cost, no waste or pollution, and no impact on material matrix. It has become one of the research hotspots at home and abroad in recent years. It must be noted that plasma modification has a time effect. The state of matter tends to transition from unstable to stable. Due to the high activity and instability of polar groups, the polar groups introduced after plasma treatment of the material surface continuously react and change with each other, as well as with the internal molecules of the material, until the material surface reaches a low energy and stable state. The existence of timeliness causes the surface properties obtained after material modification to disappear over time. The strength of timeliness is related to many factors, such as plasma treatment process parameters, material types, storage environments, etc.