Connecting Microscopic Dynamics to Macroscopic Rheology in Dynamic Covalent Composites

As compared to traditional polymer nanocomposites, incorporation of dynamic covalent chemistry at the filler-matrix interface leads to dynamic covalent composites (DCCs) with self-healing ability and improved stress relaxation. However, it is unclear how dynamic covalent bonds alter particle-scale structure and dynamics and whether these provides additional microscopic mechanisms for stress dissipation. Here, we investigate highly loaded DCCs comprising thiol-coated silica particles dispersed in a fluid matrix of ditopic benzalcyanoacetamide-based Michael acceptors. We explore how particle size and dynamic bond lifetime affect rheological stress relaxation and connect these to microscopic structure and dynamics measured by small-angle X-ray scattering (SAXS) and X-ray photon correlation spectroscopy (XPCS), respectively. We anticipate these structure-property relationships will furnish new handles by which to engineer the properties of stress-responsive composites at the molecular scale.