A nonlinear constitutive model for entangled symmetric dendrimers

Abstract

An orientation-stretch-coupled constitutive equation is suggested for symmetric Cayley tree-like dendrimers, which can self-consistently describe the linear relaxation spectrum and nonlinear viscoelastic behavior. The molecular stress is determined by orientation-stretch-coupled conformation tensors of all segments. The linear relaxation spectrum is determined according to hierarchical arm retraction with branch point hopping and dynamic tube dilation. Under strong flows, the orientation relaxation time and the stretch relaxation time are affected by the convective constraint release effect and branch point withdrawal. The coupling between segmental orientation and stretch in each generation is represented in the evolution of the coupled conformation tensor, while the possible stretch coupling among different generations is ignored. The predictions on both linear and nonlinear rheological behaviors are consistent with experiments, proving the rationality in treating coupling problems.