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- Mechanical properties (2)
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Force-deformation curves have been acquired using nanoindentation and atomic force microscopy on two amorphous polymer samples. The shape and size of the indenter tip was characterized using a white light interferometer and AFM. The measured nanoindentation curves were fitted with the Hertz equation to calculate the Young's modulus of the polymers. Once the Young's moduli of the polymers were known, AFM was used to acquire force-distance-curves on the same samples. We also used the Hertz theory for the analysis in this case. As a result, the tip radius of the AFM cantilever tip could be measured.
This procedure is proposed as a method to determine the shape and size of AFM tips for the quantitative characterization of surface forces through force-distance curves.
Thin polybutadiene/polystyrene blend films were deposited on glass substrates by spin-coating. The two polymers were chosen, as they are immiscible and differ strongly in their mechanical properties. The blend was characterized with Tapping Mode and force–distance curves. Several advantages of force–distance curves measurements compared to Tapping Mode are shown, most of all the capability of yielding quantitative information about several properties, such as Young's modulus and adhesion. Also the aging behaviour of the blend exposed to air could be observed, in particular the increase of the Young's modulus due to cross-linking and dewetting processes. Additionally, the sample was used to improve the resolution of force–distance curves up to 6 nm, which is to date the best resolution achieved with force–distance curves. Such an improvement resolves the major disadvantage of force–distance curves, compared to other scanning mode, i.e. its inferior resolution.