Multiscale Simulation of Functionalization of Surfaces using Atmospheric Pressure Discharges

Summary form only given. Pulsed atmospheric pressure plasma discharges, such as corona and dielectric barrier devices, are commonly used to functionalize surfaces (e.g., polymer sheets). The surfaces of these materials have surface roughness of 100s nm to 10s mum often resulting from the manufacturing process. For example, polypropylene surfaces consist of random assemblies of crystalline strands with diameters of 100s nm. Porous materials and textiles also have highly non-planar surfaces. The penetration of plasma generated species (electrons, ions and radicals) into surface structures is of great interest when uniform functionalization of the surface is desired. In this paper, we discuss results from a computational multiscale investigation of atmospheric pressure plasma treatment of surfaces having microstructure. The investigation was conducted with a 2-dimensional plasma hydrodynamics model using an unstructured mesh capable of resolving a dynamic range of 1000 in spatial scale. This capability enables a multi-scale approach in which the reactor scale plasma hydrodynamics and penetration of plasma produced species into surface structures can be simultaneously addressed. A surface kinetics model is integrated with the plasma hydrodynamics model to assess the uniformity of treatment on the surface structures. Investigations were preformed for discharges in atmospheric pressure air and He/O₂ mixtures, the latter being for treating surfaces when nitrogen fixing is not desired. A typical treatment geometry consists of a dielectric barrier-corona with a gap of a few mm to the surface to be treated. Surface structures have characteristic dimensions of a few mum. We found that the uniformity of treatment of polymers such as polypropylene is sensitive to the gas mixture and polarity of the discharge pulses on both macroscopic (a few mm) and microscopic (<1 mum) scales. For example, the fraction of O₂, which in turn determines the rate of forma- ion of O₃, can be used to optimize uniformity by controlling the rate of transport and reaction limited processes