Modelling diffusion induced swelling behaviour of natural rubber in an organic liquid

Liquid uptake of polymers, especially of elastomers, is associated with swelling. The swelling process is induced by diffusion and causes stresses, which interact with the diffusion again. Thus, swelling is a coupled phenomenon of mechanical behaviour and mass transport. This coupling is the focus of this paper, in which the mechanical behaviour is modelled hyperelastic for large deformations and an access for the mass transport is used with a generalised form of the chemical potential. The material behaviour of a swelling elastomer is investigated by experiments referring to the equilibrium state, when the liquid concentration in the elastomer reached a saturation level. Furthermore, swelling depends on the externally applied stress. Therefore, a continuum mechanical model is proposed with an approach of the Helmholtz free energy density. This model is implemented in a finite element software. Finally, simulation results are discussed for different boundary conditions.