Advances and New Opportunities in the Rheology of Physically and Chemically Reversible Polymers
Shilong Wu, Quan Chen
Abstract
The advances in understanding the dynamics of both the physically and chemically reversible networks are summarized from a rheological perspective. The focus is placed on linear viscoelasticity, which is related to thermodynamics and reversible kinetics at quasi-equilibrium states. We first explain basic assumptions and predictions of the reversible-network theories, including the reversible gelation, sticky-Rouse, and sticky-reptation theories. We then summarize the dynamic features of the state-of-the-art materials that have not been fully incorporated into the current theoretical framework: (1) cooperative motion of the nearby stickers significantly increases the dissociation energy of physically reversible networks, (2) the degree of gelation becomes highly T-dependent when the Gibbs free energy approaches the thermal energy for both the physically and chemically reversible networks, and (3) the exchange rate of dynamic cross-links of chemically reversible networks is reaction-controlled and depends on the chemical species and concentrations of the reactants. Finally, some pathways for future theoretical development are suggested.