Influence of tip indentation on the adhesive behavior of viscoelastic polydimethylsiloxane networks studied by atomic force microscopy

A commercial atomic force microscope (AFM) outfitted with a custom control and data acquisition system was used to investigate the adhesive nature of a viscoelastic polydimethylsiloxane (PDMS) network. Due to the complex dependence of the adhesion of this sample on factors such as indentation, surface dwell time, applied stress and sample memory effects, total control of the applied stress profile between the AFM tip and sample was necessary. Since the force curves were analyzed automatically on-line, large amounts of data could be rapidly collected, alleviating the time-consuming task of off-line analysis. The adhesive response is shown to increase with increasing interaction time and the maximum applied load. The results are rationalized by considering the time-dependent stress relaxation behavior of the PDMS network as it is deformed by the AFM tip.