Short-Time Relaxation and Anomalous Diffusion in Dynamic Covalent Networks.

Introducing dynamic covalent chemistries into polymer networks allows access to complex linear viscoelasticity, owing to the reversible nature of the dynamic bonds. While this macroscopic mechanical behavior is influenced by the dynamic exchange of these chemistries, connecting the microscopic dynamics to the bulk properties is hindered by the time scale conventional techniques can observe. Here, light scattering passive microrheology is applied to probe short-time dynamics of dynamic covalent networks that consist of telechelic benzalcyanoacetate (BCA) Michael acceptors and thiol-functionalized cross-linkers. The mean-squared displacement of probe particles embedded in the dynamic covalent networks is analyzed to explore the microscopic short-term dynamics and relaxation behavior. A series of Michael acceptors with varying equilibrium constants when reacted with thiols confirms that the observed microscopic relaxation arises from the bond dissociation. The data suggest the particles undergo local superdiffusivity, suggesting that bond breaking and bond reformation exert external force on the probe particles driving this non-Brownian anomalous diffusion.