Size effect on mechanical properties of micron-sized PS–DVB polymer particles

A nanoindentation-based flat punch method has been developed to determine the stress–strain behaviour of single micron-sized Ugelstad polystyrene-co-divinylbenzene (PS–DVB) particles in compression. Five groups of particles with identical chemical compositions but different diameters have been tested. The diameter of the PS–DVB particles varied from 2.6 μm to 25.1 μm. Constant relative deformation rate has been applied with two maximum strain levels of 5% and 10%. Results show that the particle compressive stress–strain behaviour is strongly size-dependent. The smaller the particle size is, the stiffer the particle behaves. Analyses indicate that the pre-load and adhesion during the flat punch test play a minor role on the size effect. The presence of a core–shell structure can possibly be a main contribution to the size effect. Finite element analyses have been carried out to demonstrate this surface shell effect.