Friction Force Microscopy: A Quantitative Analysis of Polymer Surfaces

Friction force microscopy (FFM) measurements have been carried out on films of poly(ethylene terepthalate) (pET) in a variety of media. In ethanol, the adhesion force is small and the frictionload relationship is linear. In perfluorodecalin, non-linear load dependence is observed and the data have been found to fit the Johnson-Kendall-Roberts model of contact mechanics. The behaviour in hexadecane is also characterised by a single asperity contact model, the DerjaguinMiiller- Toporov model. It is suggested that these differences are due to the different dielectric constants ofthe media and their influence on the strength oftip-sample adhesion. PET films have been exposed to ultra-violet (UV) light and characterised using X-ray photoelectron spectroscopy (XPS), contact angle measurement and FFM. XPS data indicated an increase in the overall oxygen content at the surface; attributed to the introduction of atmospheric oxygen. The surface coefficient of friction was found to increase over the exposure approaching a limiting value after 100 min. This increase in the microscopic properties ofthe surface reflected a change in the macroscopic properties observed by contact angle goniometry. Plasma-polymerised tetraglyme films (pP4G) have been modified by exposure to UV light and characterised using XPS and FFM. XPS data have shown that the ether component of the CIs spectrum declines after UV exposure, while carbonyl and carboxylate contributions increase. The coefficient of friction increased, reaching a limiting value after 10 min, in agreement with ether and carboxylate components in the CIs spectra. Samples exposed to UV light through a mask yielded excellent frictional contrast. When immersed in solutions of proteins labelled with fluorescent markers, patterns were formed yielding excellent fluorescence contrast when characterised by confocal microscopy. The exposed areas became adhesive towards proteins, while the masked areas remained resistant. Sub-micron structures as small as 338 nm were formed via scanning near-field photo-lithography; resulting features were used to immobilise proteins, suggesting an effective route to the formation of sub-micron protein patterns.EThOS - Electronic Theses Online ServiceGBUnited Kingdo