Fluorine Plasma Treatments of Poly(propylene) Films, 2 – Modeling Reaction Mechanisms and Scaling

Abstract

AbstractThe surface properties of commodity hydrocarbon polymers such as poly(propylene) (PP) can be modified by functionalization with plasma‐generated radicals and ions. For example, affixing fluorine to a hydrocarbon surface lowers surface energy and increases hydrophobicity. One such process is treatment of PP films in low‐pressure, capacitively coupled plasmas (CCPs) sustained in F2‐containing gas mixtures. F atoms produced in the plasma abstract H atoms from the hydrocarbon and passivate the resulting alkyl sites producing CFn sites. Energetic ion and photon fluxes sputter and initiate crosslinking. In this paper, the plasma fluorination of PP in a CCP sustained in Ar/F2 is discussed with results from a two‐dimensional plasma hydrodynamics model. The surface reaction mechanism includes a hierarchy of H abstraction and F/F2 passivation reactions, as well as crosslinking, and ion and photon‐activated processes. Predictions for surface composition were compared to experiments. We found that the lack of total fluorination with long plasma exposure is likely caused by crosslinking, which creates CC bonds that might otherwise be passivated by F atoms. Increasing steric hindrances as fluorination proceeds also contribute to lower F/C ratios.magnified image