(621e) Dynamic Polymer Nanocomposites Engineered Via Particle-Based Crosslinks

Inherent self-healing properties make materials formed from noncovalent networks attractive as they can repair fractured surfaces facilitated by highly mobile chain segments and by possibilities of achieving fast reversible associations at ambient conditions. However, noncovalent networks are prone to creep and considerable material deformation on loading, which makes these materials unsuitable for many applications. Stronger bond strengths lead to better mechanical properties, but the reaction kinetics of reversible bonds become slower and self-healing becomes less efficient. Multivalent binding of ligands on one entity via noncovalent interactions is collectively much stronger and display qualitatively different properties than those of underlying monovalent interactions. Here, we introduce the concept of multivalency in crosslinking mechanisms using surface-functionalized nanoparticles to make noncovalent networks with improved mechanical properties. In general, positive cooperative interactions enhance the bond strengths of weak, monovalent supramolecular bonds, but they lead to a slower healing rate. First, a new type of dynamic, noncovalent networks with enhanced bond strength is developed by introducing the concept of particle-based crosslinks and systematically studying the effect of positive cooperativity in polymer networks. Secondly, these materials are designed to have access to two or more thermodynamic states where the bond dynamics of polymer networks are reversibly programmed using tunable interfacial interactions between nanoparticles and polymers. The underlying hypothesis is that the number of binding events between nanoparticles and polymers and the strength of interfacial interactions exhibit non-linear relationship, which will be tested by measuring the crosslink’s bond exchange rate and bulk mechanical properties.