MICROSCOPIC ORIGINS OF THE INTERFACE FRICTION OF ORGANIC FILMS - THE POTENTIAL OF VIBRATIONAL SPECTROSCOPY

This paper begins by reviewing the history of interface friction of organic films in terms of the measurement and interpretation of these phenomena using microscopic models. The interface friction is considered to arise from the shear or flow of the organic film and the prime characteristic is taken as the interface shear stress, denoted as tau. The influence of contact pressure, temperature and sliding velocity is described in general terms. The essence of the established models is based upon the belief that microscopic entities, such as side groups or chain segments, are engaged within the shear plane and thereby transfer frictional work into the film which is ultimately dissipated as heat by phonon wave damping. The value and success of these models is assessed. An alternative approach is suggested which seeks to use vibrational spectroscopy as a means of identifying the characteristics of the microscopic units active in the shear plane. The data are preliminary, but indicate that this method has potential for identifying the species responsible for accommodating the microscopic strain and also for characterizing the environment in which these species flow.