Consequences of Ion and Photon Fluxes on the Low-Pressure Plasma Fluorination of Polypropylene

Summary form only given. The surface energy and adhesion properties of commodity polymers such as polypropylene (PP) can be controlled by functionalization of the surface layers in plasmas. Affixing fluorine lowers surface energy and increases hydrophobicity. One such fluorination process is the immersion of PP sheets in a low pressure, capacitively coupled discharge sustained in F2 containing gas mixtures wherein F atoms both abstract H atoms from and adhere to the surface. In these plasmas, the PP is subject to both energetic ion and photon fluxes. In this talk, the consequences of ion and photon bombardment during low-pressure plasma fluorination of PP will be discussed with results from computational and experimental investigations. PP was treated on a mewing web in low pressure (< a few Torr) capacitively coupled plasmas sustained in gas mixtures containing F2. The fractional coverage of surface resident groups (CH, CF, CF2, CF3) was measured using FSCA. Plasma and surface processes on the moving web were simulated using a 2-dimensional plasma hydrodynamics and surface chemistry model. In the surface reaction mechanism, apart from a hierarchy of reactions beginning with H abstraction by F atoms and followed by passivation by F and F2, ion (sputtering, scission) and photon (H abstraction, scission) activated processes are included. Ion sputtering rates were determined by TRIM while rates of photon activation processes were parameterized. Comparisons will be made between the model and experiments for surface coverages of =CH and =CFn. Preliminary results have shown that the surface coverage of =CH is a sensitive function of ion energy, a consequence of sputtering of previously fluorinated sites and the slow re-fluorination of underlying sites that are sterically hindered.