Plasma-surface treatment is a technique to treat surfaces of various materials for a wide variety of applications. However, it has been often said that the altered nature of the plasma-treated surface does not last long. The reasons for the decay of plasma treated surfaces are considered to be (1) rotation and migration of surface moieties containing functional groups into inside of the material and (2) disappearance of relatively low-molecular-weight substances including weak boundary layer (WBL) formed in the plasma treatment. However, the decay behavior depends on materials nature, plasma condition, storage condition, and so on, and the precise mechanism is still unknown. The decay also occurs on inorganic material surfaces, and some post-reactions take place even on the plasma-polymerized film surfaces. Since plasma-treated surfaces are very thin and possess a number of active sites, a promising method to prevent the decay, at the present stage, may be immobilization of proper polymers on the surface, such as plasma-induced graft polymerization.
