Relaxation in network materials: the contribution of the network

Stress relaxation in network materials is controlled by the relaxation of the network structure, the migration of solvent and the viscoelasticity of the embedding matrix. In this work we focus on the contribution of the network to this process. To this end, we consider athermal random networks in which fibers behavior is described by a Maxwell model and monitor the relaxation on network scale. We observe a behavior similar to that reported in many glass formers close to Tg: two relaxation regimes, of which the early time relaxation is exponential, while the late times are described by a stretched exponential. We study the dependence of the stretch exponent on network parameters and observe the maximum slowdown in networks at the transition between the affine and non-affine regimes. The parameter controlling the physical nature of relaxation in this athermal system is a non-dimensional group which is also used to distinguish between affine and non-affine networks. This parameter replaces temperature which plays a similar role in thermal systems. Direct microscopic observations of the dynamics support this physical picture.