Quantitative evaluation of nano-mechanical properties at polymer surfaces based on scanning viscoelasticity microscopy

A mechanical model analysis for scanning viscoelasticity microscopic (SVM) measurement under various conditions was carried out to quantitatively evaluate spring constants of polymer surfaces. Experiment was made at room temperature using polystyrene films with different molecular weights. When the sample surface was in a glassy state, that is, in an elastic regime, a series model composed of two springs with a cantilever and the sample surface could well express the SVM vibration system. In contrast, when the surface was in a viscoelastic regime, a viscous component must introduced into the model in order to analyze the experimental results. Based on fitting parameters for the analysis, the spring constants for the PS surfaces were successfully extracted. Consequently, the spring constants of the surfaces were lower than the bulk value by a few decades. Finally, it can be claimed that surface nano-mechanical properties are essentially different from the corresponding bulk ones.