Polymeric thin shells: Measurement of elastic properties at the nanometer scale using atomic force microscopy

We conducted atomic force microscopy nanocompression tests on thin-walled hollow microspheres in aqueous conditions. The microspheres used for this study consist of a ∼10 nm soft gel skin and an inner ∼40 nm stiff polymeric shell. The resulting force–deformation curves revealed an initial small-range non-linear repulsion associated with the soft ultrathin outer layer followed by a linear regime which was used to calculate the Youngʹs modulus of the stiff thin wall. The linear regime is of the order of the shell thickness and the elastic modulus deduced using the linear Reissner relationship is comparable to the corresponding bulk polymer modulus. At larger deformations, we observed near-linear behaviour zones of similar slope separated by various non-linearities, steps and jumps which are associated with buckling events.