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The combination of wettability, X-ray photoelectron spectroscopy and scanning force microscopy has been used to analyse the changes to the surface after plasma treatment of poly(ethylene terephthalate) film. Calculations on contact angle data with a combination of polar and non-polar liquids have shown that argon plasma treatment considerably enhances the work of solid-(polar) liquid adhesion and the surface free energy of the films due to the creation of acidic and basic functions on the polymer surface. In contrast, Lifshitz-van der Waals (apolar) interactions decrease slightly as a consequence of plasma-induced chain-scission. We present the first study of a plasma-treated polymer by chemical force microscopy. Plasma-modified surfaces exhibit substantially higher friction than untreated material and are more easily disrupted by the movement of the tip during scanning. Friction is reduced when methyl-functionalised tips are employed. There is a correlation, on plasma treatment, between the rapid increases in surface friction probed by lateral force microscopy and surface free energy probed by wettability and X-ray photoelectron spectroscopy. The modified mechanical properties and polar group incorporation both result from scission of polymer chains and contribute to the lateral force contrast.

Contact mode scanning force microscopy of plasma-treated poly(ethylene terephthalate) leads to poor resolution of surface features due to the disruption of delicate structures. However, non-contact mode imaging reveals important new insights into the development of the surface topography with plasma treatment. While the surface wettability reaches a steady state after only a few minutes, SFM reveals subtle topographical developments extending over a period of hours. Using a model polyester containing particulate surface additives, we demonstrate that the rate of erosion of the polymer during plasma treatment may be precisely quantified, and show that at 0.1mbar Ar pressure, PET is eroded at 4nmmin1. This high erosion rate persists beyond the point at which the wettability of the polymer has reached a limiting value. Ultimately, the rate of erosion slows. At high treatment times the surface exhibits ridges that align perpendicular to the final draw direction of the film. We speculate that these arise from the preferential erosion of amorphous material.