Viscoelastic response of poly(dimethylsiloxane) in the adhesive interaction with AFM tips.

As follow-up to a previous study,(1) the viscoelastic response of cross-linked poly(dimethylsiloxane) (PDMS) in the adhesive interaction with AFM tips is reported. The indentation of the AFM tip into the polymer caused by adhesion is monotonically dependent on the loading speed. During the unloading process, the adherence force between the AFM tip and the polymer has a turning point at a specific unloading speed. It is found that the viscoelastic relaxation processes in the bulk polymer, which may have more than one component, cause the monotonic rate dependence of the adhesion-induced indentation; the competition between the bulk relaxation and the interfacial relaxation results in the turning point of the adherence force at a specific ramp speed. Experiments at different dwell times provide additional evidence for the existence of material relaxation. Methyl- and hydroxyl-functionalized AFM tips were used to study PDMS samples and indicated strong dipolar attractions formed at the tip-sample interface.