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 mu m to 25.1 mu m. 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. (C) 2008 Elsevier Ltd. All rights reserved.