We use a displacement-controlled dual double-cantilever-based surface-force-type apparatus to dynamically probe perfluorooctyl trichlorosilane monolayers self-assembled on aluminum and silicon substrates of 1nm and 0.7nm rms (root mean square) roughness, respectively, using a 1.12mm diameter ruby sphere of 0.25nm rms roughness. We record stiffness and damping constant as a function of compression load and deconvolute the elastic modulus using contact mechanical formulations. When mechanical intervention is limited to the terminal end of the molecule there is a strong viscous response and a low level of elastic response in consonance with the ability of the molecule to generate conformational defects freely. When the intervention penetrates into the molecular backbone the damping disappears dramatically and the molecule registers at a contact mean pressure of about 0.2GPa a monotonic and steep rise in elastic resistance in response to further intervention by the probe. We offer a physical explanation of the process and describe this change as due to a phase transition from a liquidlike to a solidlike state as indicated by a large increase in relaxation time constant. © 2005 The American Physical Society.