Morphology and Conductivity in Ionic Liquid Incorporated Sulfonated Block Copolymers

Abstract

We have explored the link between morphologies and conductivities for ionic liquids (ILs) incorporated block copolymer electrolytes by combining small-angle X-ray scattering, transmission electron microscopy, and impedance spectroscopy. The block copolymer electrolytes investigated in present study are a series of partially sulfonated poly(styrenesulfonate-b-methylbutylene) (S(n)MB(m)) copolymers with different molecular weights and sulfonation levels (SLs). Imidazolium-based Its are selectively doped into hydrophilic domains of S(n)MB(m) copolymers, and various morphologies have been observed as a function of the amount of absorbed ILs and SLs in S(n)MB(m) copolymers. We have demonstrated that the morphologies of ILs impregnated S(n)MB(m) copolymers are sensitive function of kinds of counteranions in IL, yielding remarkable discrepancy in conductivities. When the morphology of sample is appeared to be a lamellar structure, significant reduction in through-plane conductivity value was detected due to the nonrandom orientation of microdomains. In contrast, hexagonally perforated lamellar forming samples exhibit the highest conductivities in both through-plane and in-plane directions on account of the better connectivity of ionic domains along the perforated hydrophilic phases. Once the morphology effects were vanished by employing highly sulfonated S(n)MB(m) copolymers, it has been revealed that the conductivities of Its incorporated copolymers are closely related to the polarity of ILs as confirmed by solvation dynamics study.