Interfacial Reaction Induced Disruption and Dissolution of Dynamic Polymer Networks

Using Nanosphere Embedding to Probe the Surface and Bulk Relaxation in Vitrimers

The relaxation behavior of vitrimers that is dominated by chemical exchange reactions plays a critical role in vitrimer processing and applications such as self-healing, welding, and others involving the dynamic nature of the vitrimers. Here, we use atomic force microscopy to image embedding of gold nanospheres into epoxy-based vitrimers to assess the surface and bulk relaxation in this material. The results show that even at temperatures well below the bulk topology freezing transition temperature, the nanospheres embed into the vitrimers. The activation energy for the relaxation at the surface and in bulk were estimated in the single measurement, and the former is found to be much lower than the latter. The increase in the surface relaxation is attributed to a combination of an acceleration effect on relaxation by network defects and a decrease in the number of intermolecular exchanges at the surface.

Catalyst Control of Nanoscale Characteristic Length of the Glass Transition in Organic Strong Glass-Formers

We report the nanoscale characteristic length (ξ_α) in organic strong glass-formers at glass transition. Catalyst-dependent ξ_α of the epoxy-based covalent adaptable networks (CANs) is observed, that is, the more efficient the catalyst for the cross-linking reactions, the larger the ξ_α is, and upon thermal heating, the more broad the glass transition will be. The observed structural properties at glass transition can be correlated with the topology freezing transition where the fluctuations of network topology aroused from the bond exchange reactions are frozen. This study proposes the catalyst-dependent structural properties in CANs and may fill the structural gap between the glass transition and topology freezing transition of organic strong glass-formers.