Microcapsule mechanics: Quasi-static compressive properties and the effect of liquid core

Liquid-filled microcapsules with a core-shell structure have been developed and widely applied in multi-functional materials. Mechanical properties of microcapsules play a vital role in production, collection and re-processing. Nevertheless, their mechanical behaviors have not been comprehensively understood. In this study, poly urea-formaldehyde (PUF) shelled microcapsules with paraffin oil are selected for experiments. Intrinsic mechanical properties of the shell material obtained from nanoindentation test and uniaxial compression test show remarkably good consistence. Both experimental and simulation results unprecedentedly reveal that the liquid core has a significant effect on the mechanical properties of a microcapsule by enhancing the stability and facilitating the stretching of the shell under compression, especially at large deformations. Moreover, the relationship between the rising hydrostatic pressure and the structural deformation is found to nicely follow up a quadratic function. When the structural deformation increases, plasticity successively appear at the circular contact area, contact edge, and non-contact area of the shell.