Measurement of the mechanical properties of thin films mechanically confined within contacts

This study addresses the problem of the measurement of the mechanical properties of thin films using contact mechanics methods. In a first stage, an analytical contact model recently developed by Perriot and Barthel [A. Perriot and Barthel, E. J. Mat. Res, 2004. 19(2): 600-608] is used to derive a first order approximation within the limits of confined geometries. Together with indentation experiments using polymer films on elastic substrates, this approach demonstrates the essentially oedometric nature of the coating's response, provided it is not to close to incompressibility. In a second stage, an extension of this approximate description to lateral contact loading allowed to relate the contact stiffness to the shear modulus of the film. This approach was successfully applied to the determination of the viscoelastic modulus of an acrylate polymer film in the glass transition zone of the film, with an emphasis on its sensitivity to hydrostatic pressure. This study suggests that lateral contact experiments are more appropriate than indentation ones for the measurement of film properties close to incompressibility.