Thermoreversible Ion Gel with Tunable Modulus Self-Assembledby a Liquid Crystalline Triblock Copolymer in Ionic Liquid.

Iongels with tunable storage moduli are prepared through the self-assemblyof an ABA triblock copolymer AOA-12 comprised of a thermotropic liquidcrystalline (LC) polymer as the end-block A and poly(ethylene oxide)(PEO) as the mid-block B in a room-temperature ionic liquid (IL),1-ethyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide([EMIM][TFSI]). The PEO mid-block is well-solvated by this ionic liquid,whereas the LC polymer end-blocks aggregate and serve as the physicalcross-linkers. For comparison, a triblock copolymer AOA-0 containinga non-LC side-chain polymer with the same mesogen is also synthesized,and its corresponding ion gel is prepared. The ion gels with relativelyhigh concentrations of the LC triblock copolymer have hierarchicalstructures with different microphase-separated nanostructures andthe LC arrangement of the LC blocks. By incorporating the azobenzenemesogen in the side chains, transparent AOA-n/[EMIM][TFSI](where nis the number of carbon atoms in the spacerbetween the azobenzene mesogen and the polymethacrylate backbone,and n= 0, 12), ion gels are obtained with concentrationsof the polymer as low as around 2 wt %. The ion gel obtained has astorage modulus as high as ∼10 kPa, while its conductivityis close to that of the pure IL mainly because of the high IL concentrationof the ion gel. Furthermore, the storage modulus of the AOA-12/ILion gel can be tuned by temperature because of the thermotropic phasebehavior of the LC block. These ion gels are potentially useful ashigh-temperature ionic membranes or thermal-responsive soft actuators. [ABSTRACT FROM AUTHOR]