Self-consistent modeling of entangled network strands and linear dangling structures in a single-strand mean-field slip-link model

Linear viscoelastic (LVE) measurements as well as non-linear elongation measurements have been performed on stoichiometrically imbalanced polymeric networks to gain insight into the structural influence on the rheological response (Jensen et al., Rheol Acta 49(1):1-13, 2010). In particular, we seek knowledge about the effect of dangling ends and soluble structures. To interpret our recent experimental results, we exploit a molecular model that can predict LVE data and non-linear stress-strain data. The slip-link model has proven to be a robust tool for both LVE and non-linear stress-strain predictions for linear chains (Khaliullin and Schieber, Phys Rev Lett 100(18):188302-188304, 2008, Macromolecules 42(19):7504-7517, 2009; Schieber, J Chem Phys 118(11):5162-5166, 2003), and it is thus used to analyze the experimental results. Initially, we consider a stoichiometrically balanced network, i.e., all strands in the ensemble are attached to the network in both ends. Next we add dangling strands to the network representing the stoichiometric imbalance, or imperfections during curing. By considering monodisperse network strands without dangling ends, we find that the relative low-frequency plateau, G(0)/G(N)(0), decreases linearly with the average number of entanglements. The decrease from G(N)(0) to G(0) is a result of monomer fluctuations between entanglements, which is similar to longitudinal modes in tube theory. It is found that the slope of G' is dependent on the fraction of network strands and the structural distribution of the network. The power-law behavior of G '' is not yet captured quantitatively by the model, but our results suggest that it is a result of polydisperse dangling and soluble structures.