Lyotropic Phase Behavior of Coil-Bottlebrush Diblock Copolymers in Alkylimidazolium-Based Ionic Liquids

Block copolymer melts self-assemble into 3D network (NET) nanostructures, exhibiting useful, nonlinear combinations of the properties of their constituents. However, chain packing frustration limits NET formation to specific and narrow composition windows in linear diblocks. While recent work has demonstrated that the location of the NET window in coil-block-bottlebrush diblocks may be tuned by varying the brush architecture, the composition window remains narrow. Aiming to widen access to NETs, we explore the lyotropic self-assembly of coil-block-bottlebrush diblocks in the presence of coil-selective N-alkyl-N′-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids [C_xMIM][TFSI], where C_x is an n-alkyl substituent with x = 1, 4, 6, 8, 10, or 12 carbons. Morphological analyses of these IL lyotropic assemblies based on diblocks with coil volume fractions f_coil ≈ 0.38 indicate the formation of various coexisting morphologies. Despite significant variations in solvent selectivity with x, the lyotropic phase behavior exhibits a surprisingly weak dependence on IL identity.