Solute Diffusivity and Local Free Volume in Cross-Linked Polymer Network: Implication of Optimizing the Conductivity of Polymer Electrolyte

YC Tsai and CC Chiu, POLYMERS, 14, 2061 (2022).

DOI: 10.3390/polym14102061

The diffusion of small molecules or ions within polymeric materials is critical for their applications, such as polymer electrolytes. Cross- linking has been one of the common strategies to modulate solute diffusivity and a polymer's mechanical properties. However, various studies have shown different effects of cross-linking on altering the solute transports. Here, we utilized coarse-grained molecular dynamics simulation to systematically analyze the effects of cross-linking and polymer rigidity of solute diffusive behaviors. Above the glass transition temperature T-g, the solute diffusion followed the Vogel- Tammann-Fulcher (VTF) equation, D = D-0 e(-Ea /R(T-T0)). Other than the conventional compensation relation between the activation energy E-a and the pre-exponential factor D-0, we also identified a correlation between E-a and Vogel temperature T-0. We further characterized an empirical relation between To and cross-linking density. Integrating the newly identified correlations among the VTF parameters, we formulated a relation between solute diffusion and the cross-linking density. The combined results proposed the criteria for the optimal solute diffusivity in cross-linked polymers, providing generic guidance for novel polymer electrolyte design.

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