Correlation between Ionic Mobility and Microstructure in Block Copolymers. A Coarse-Grained Modeling Study

Molecular simulations of coarse-grained diblock copolymers (DBP) were devised to unveil correlations between microstructure and ionic mobility (μ) in the limit of high salt dilution. It is found that three key microstructural features had a significant effect on ion transport: the extent of microdomains mixing (β), the local unit-cell tortuosity of the conductive domain (λ), and the local fluctuations in the density (ρ) of the polymer matrix. While the β effect has been previously studied in some detail for lamellae morphology, the effects of ρ nonhomogeneities and λ have received much less attention. To control the local fluctuations in ρ, a polymer design variant is explored that incorporates a second conductive block (A′) that is incompatible with the other two blocks (A′–A–B). It is found that increasing the fraction of A′ beads increases the frequency and amplitude of the local ρ depleted regions within the conductive domain, resulting in an increase in μ. Additionally, the effect of morphology on μ was examined by varying the volume fraction of the constitutive blocks and utilizing the different blocks as the conductive domains. It is shown that μ for various defect-free morphologies and chain lengths can be correlated to β and λ via a single universal curve.