Tapping mode force microscopy imaging of elastic properties of core-shell latex particles.

In this study films of core-shell-structured latex particles are investigated by dynamic scanning force microscopy 'tapping mode imaging'. Polymer dispersions with cores of the low-viscosity polymer poly(2-ethylhexyl methacrylate) (PEtHMA) and shells of the cross-linked rubber poly(n-butyl acrylate) (PBA) were spread on a flat mica surface to form a monolayer. Topographic as well as phase images were recorded at different amplitudes and damping factors (so-called soft and hard tapping). The topographic images show a continuous matrix formed by the particles, but a clear contrast of individual particles in the phase images could be obtained at high damping factors of the cantilever oscillation. The soft cores embedded in the matrix of the shell polymers caused a perceptible reduction of the phase of oscillation. Consequently, the total particle appeared soft enough because it allowed deformation of the soft cores below.