Thermoreversible Ion Gels with Tunable Melting Temperatures from Triblock and Pentablock Copolymers

Abstract

We demonstrate a way to tune the critical gelation temperature (Tgel) for thermoreversible ion gels. Thermoreversible ion gels were prepared previously through the self-assembly of poly(N-isopropyl acrylamide-b-ethylene oxide-b-N-isopropyl acrylamide) (PNIPAm-PEO-PNIPAm) triblock copolymers in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). The resulting Tgel was 17 °C, as judged by the intersection of the dynamic moduli (G‘ and G‘ ‘) at a fixed low frequency on increasing the temperature. These gels are of interest in various applications, including gate dielectric materials in organic field effect transistors. However, it is desirable to bring the Tgel significantly above room temperature in order to realize device applications. By incorporating solvatophobic blocks of polystyrene (PS) into the PNIPAm-PEO-PNIPAm triblock copolymers to produce well-defined PNIPAm-PS-PEO-PS-PNIPAm pentablock copolymers, we are able to adjust the Tgel of the re...