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The mechanical properties of seven types of silicone methacrylate microparticles prepared by solution polymerization with a Pickering emulsifier were investigated by Atomic Force Microscope force–displacement curves acquired in air with the Colloidal Probe Technique, i.e., with spherical SiO2 particles of known radius glued on tipless cantilevers. The deformation curves derived from the force–displacement curves were fitted with Hertz equation for the contact between two spherical particles, which lead to the determination of the elastic modulus of the samples.
The performed measurements and the analysis provide quite exact values of the elastic modulus of all investigated polymer particles. Moreover, the results of the measurements were repeatable over large time intervals, also with different experimental setups. The influence of the sample preparation (polymerization method, cross-linking density of the polymer, and thickness of the external shell of the Pickering emulsifier) is discussed as well. The elastic moduli correlate with the cross-linking density (from 2 MPa for low cross-linking density up to 100–130 MPa for medium cross-linking density), whereas the thickness of the external shell formed by the Pickering emulsifier has no measurable influence on the mechanical properties of the microparticles.
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.