Short-Time Relaxation and Anomalous Diffusion in Dynamic Covalent Networks

Area of Science:

• Polymer Chemistry
• Materials Science
• Physical Chemistry

Background:

• Dynamic covalent chemistries enable complex polymer network viscoelasticity through reversible bonds.
• Connecting microscopic dynamics of bond exchange to bulk properties is challenging due to limited observation timescales.

Purpose of the Study:

• To investigate the short-time dynamics of dynamic covalent networks using light scattering passive microrheology.
• To link microscopic relaxation behavior to the specific dynamic covalent chemistries employed.

Main Methods:

• Utilized light scattering passive microrheology to probe short-time dynamics.
• Analyzed mean-squared displacement of embedded probe particles in dynamic covalent networks.
• Synthesized networks using benzalcyanoacetate (BCA) Michael acceptors and thiol-functionalized cross-linkers with varying equilibrium constants.

Main Results:

• Observed microscopic relaxation behavior directly correlated with bond dissociation, confirmed by varying equilibrium constants.
• Probe particles exhibited local superdiffusivity within the networks.
• Evidence suggests bond breaking and reformation exert forces on particles, driving anomalous diffusion.

Conclusions:

• Microscopic dynamics in these dynamic covalent networks are governed by the dissociation and reformation of dynamic bonds.
• The observed superdiffusive motion of probe particles is a direct consequence of these bond dynamics.
• Passive microrheology is effective in probing short-time dynamics and linking molecular events to macroscopic behavior.