Deformation-induced domains in silicone rubber

In-situ X-ray computed tomography observations show the development of spatially heterogeneous deformation in cylindrical silicone rubber specimens subjected to a spatially uniform axial strain. Using a doping agent, we demonstrate that this heterogeneity is associated with the motion of a mobile phase within the silicone rubber. The mobile phase is hypothesised to behave like a liquid crystal, with heterogeneity driven by the formation of nematic domains within it. A constitutive model for the deformation of a rubber with such a mobile phase is presented and analysed for axisymmetric uniaxial loading. An important outcome of this analysis is a phase map showing three regimes of behaviour under uniaxial deformation. Spatial heterogeneity develops due to a switch in the orientation of the mobile phase molecules, resulting in the formation of mechanically induced domains within the rubber. Consistent with observations, the model predicts that imposed tensile strains can result in volume loss in the core of the cylindrical specimen and dilation in the outer shell, whereas imposed compressive axial strains reverse this trend.