Correlation between Ionic Mobility and Microstructure in Block Copolymers. A Coarse-Grained Modeling Study
MS Alshammasi and FA Escobedo, MACROMOLECULES, 51, 9213-9221 (2018).
Molecular simulations of coarse-grained diblock copolymers (DBP) were devised to unveil correlations between microstructure and ionic mobility (mu) 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 (beta), the local unit-cell tortuosity of the conductive domain (lambda), and the local fluctuations in the density (rho) of the polymer matrix. While the beta effect has been previously studied in some detail for lamellae morphology, the effects of rho nonhomogeneities and lambda have received much less attention. To control the local fluctuations in rho, 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 rho depleted regions within the conductive domain, resulting in an increase in mu. Additionally, the effect of morphology on mu was examined by varying the volume fraction of the constitutive blocks and utilizing the different blocks as the conductive domains. It is shown that mu for various defect-free morphologies and chain lengths can be correlated to beta and lambda via a single universal curve.
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