Network structure influences bulk modulus of nearly incompressible filled silicone elastomers

Christopher W. Barney, Matthew E. Helgeson, and Megan T. Valentine. Extreme Mechanics Letters, 52:101616 (2022).

Abstract

The bulk modulus is a fundamental elastic property that quantifies a material’s resistance to changing volume and is critical in loading situations where significant hydrostatic stresses develop. Rubbery polymer networks represent a class of nearly incompressible materials whose bulk modulus is orders of magnitude larger than the tensile elastic modulus. The current physical understanding of the bulk modulus in nearly incompressible polymer networks suggests that it is insensitive to structural features of polymer networks, such as the network topology and spatial distribution of crosslinks and chains; however, there is a lack of experimental evidence available in the literature to thoroughly examine this understanding. In this work, radially confined compression is used to quantify the bulk modulus of silicone blends with variable crosslinking density and sol fraction. These measurements demonstrate that the bulk modulus is systematically altered when changing the network structure. Poisson’s ratio of the silicone blends is also characterized. These findings provide a deeper understanding of the connection between bulk modulus and molecular structure of nearly incompressible polymer networks.