Radical generation and surface functionalization of polymers in flowing atmospheric pressure pulsed discharges

Summary form only given. Corona and dielectric barrier discharges operating at atmospheric pressure are often used to functionalize polymer surfaces. The generation and transport of plasma species (electrons, ions and radicals) close to the surface determines the rate of surface reactions that result in functionalization. Under conditions of forced gas flow in such discharges, the plasma dynamics can be disrupted and the relative abundance of the different reactive gas species close to the surface may vary. The effect of forced gas flow on radical generation and surface kinetics is discussed using results from a computational multiscale investigation of atmospheric pressure plasma treatment of surfaces. The modeling platform consists of a 2-dimensional plasma hydrodynamics model using an unstructured mesh with a spatial range of resolution of approximately 1000, coupled to a surface kinetics model and a fluid dynamics model. Investigations were performed for atmospheric pressure treatment of polypropylene surfaces using He/O₂ mixtures in two different repetitively pulsed dielectric barrier-corona configurations. These configurations differ in the manner of gas injection, laterally or radially. Without forced gas flow, diffusion is the only mechanism for transport of radicals near the surface, and so treatment is largely limited to the extent of the plasma. Local gas heating may also become problematic. With forced gas flow, typically a few slpm, the local rate of production of radicals in the plasma zone increases while convective transport enhances densities downstream beyond the plasma zone. This enables gas phase reactions to proceed for a longer period of time before reacting with the surface. It may thus be possible to use the gas flow rate to selectively design the composition of the radical flux, alter the dominant surface reaction pathways and so optimize surface functionalization