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The frictional properties of spun-cast films of polystyrene and poly(methyl methacrylate) (PMMA) have been characterized using friction force microscopy (FFM). In air, the friction-load relationship was found to obey Johnson-Kendall-Roberts mechanics, but under ethanol, it was found to fit Amontons' Law. The coefficient of friction measured under ethanol was found to increase with increasing molecular weight, up to a molecular weight close to the bulk critical molecular weight for entanglement. At greater values than this, the coefficient of friction changed comparatively little with molecular weight. It is suggested that at molecular weights below Mc, the frictional interaction is dominated by plowing of the tip between polymer molecules; as molecular weight increases, so the viscosity of the film increases and the coefficient of friction increases. After the onset of entanglement, the mechanism of energy dissipation changes to one in which the tip sticks in loops of polymer between entanglements, extending the chains until at a critical stress, the contact is broken. The frictional interaction is thus comparatively invariant with molecular weight. FFM was also used to investigate the kinetics of the UV-induced modification of PMMA. A progressive decrease in the coefficient of friction was observed as a function of the time that the film was exposed to UV light, a result which was correlated to a gradual reduction in the molecular weight of the polymer and, hence, the entanglement density of the system.

Central to the advancement of friction force microscopy (FFM) as a quantitative surface analysis technique is the establishment of clear relationships between the organization and composition of surfaces and data acquired from FFM. As a step toward this goal, FFM has been applied to measurement of the kinetics of a surface-confined reaction, namely, the esterification of alcohol-terminated self-assembled monolayers (SAMs) by trifluoroacetic anhydride. The kinetics were studied initially using contact angle goniometry. The data obtained were found to be well described by a Langmuir adsorption isotherm. The progress of the reaction was also monitored by X-ray photoelectron spectroscopy, and comparative studies carried out using FFM. By using a simple numerical analysis of the FFM data, it has been possible to obtain quantitative information on surface composition. The resulting measurements of the fraction of derivatized molecules have been compared with compositional data obtained from XPS and contact angle goniometry, and found to be in excellent agreement, establishing unequivocally the capability of FFM as a quantitative surface analysis technique.