Ion-Conductive Nanostructured Polymer Films Formed by Photopolymerization of Lyotropic Columnar Liquid-Crystalline Monomers, Composed of a Zwitterionic Compound and a Protic Ionic Liquid

Abstract

Here, we report on a new family of columnar nanostructured polymer films forming protic nanochannels that exhibit good ionic conductivities in the order of 10−4–10−3 S cm−1 at ambient temperature. These polymer films were obtained by the in situ photopolymerization of lyotropic columnar liquid crystals, consisting of a polymerizable taper-shaped zwitterionic compound and a protic ionic liquid (imidazolium bis(trifluoromethylsulfonyl)imide), in the presence of 15 wt% water. The composition of the protic ionic liquid in the mixture was changed from 40 to 60 mol%. The ionic conductivities were measured by an alternating current impedance method. The ionic conductivity increased with the increase of the protic ionic liquid. The conductivities of columnar nanostructured polymer films were about 2–3 orders of magnitude higher than those of amorphous polymer films prepared by photopolymerization of the corresponding monomers in an isotropic liquid state. The formation of nanochannels in the polymer matrices significantly enhanced the ion conduction. The present two-component lyotropic liquid-crystalline self-assembly followed by photopolymerization is a promising approach to the development of high ion-conductive polymer membranes.

Ionic electroactive PEDOT:PSS/liquid-crystalline polymer electrolyte actuators: photopolymerization of zwitterionic columnar liquid crystals complexed with a protic ionic liquid

“…Compound 1 alone showed no LC properties. 47 In contrast, M1/2(40) , M1/2(50) , and M1/2(60) exhibited columnar LC phases (Col) at room temperature. For example, M1/2(60) shows a fan-shaped texture characteristic of columnar phase, as demonstrated in Fig.…”

“…Compound 1 was synthesized according to our previous paper. 47 1-Butyl-3-methylimidazolium hydrogen sulfate ( 2 ) was purchased from Tokyo Chemical Industry (Japan). 2,2-Dimethyl-2-phenylacetophenone and 2,6-di- tert -butyl- p -cresol were purchased from Kanto Chemical (Japan).…”

“…High proton conductivities on the order of 10 À3 -10 À1 S cm À1 at room temperature were achieved for photopolymerized columnar and bicontinuous cubic LC films consisting of zwitterionic LC molecules and protic salts in the presence of water. 27,47 In this work, the ionic mobility in the columnar assemblies based on the zwitterion-protic ionic liquid mixture would slow down under anhydrous conditions. On the other hand, the previously designed nonprotic ionic LC molecule having photopolymerizable groups cannot form columnar assemblies with more than 50 mol% of ionic liquid due to the weaker intermolecular interactions.…”

“…45,46 In addition, we also developed 1D proton-conductive LC polymer membranes through in situ photopolymerization of aqueous lyotropic columnar LC phase of polymerizable zwitterionic molecule and imidazolium bis(trifluoromethylsulfonyl)amide as a protic solid salt. 47 The membrane containing 60 mol% protic salt exhibited a high conductivity reaching 10 −3 S cm −1 at 30 °C. These results strongly motivate the further development of high strain and high-power iEAP actuators based on zwitterionic LC assemblies.…”

Industrial Applications of Ionic Liquids

“…Furthermore, the amphiphilic nature of many ILs can induce self-assembly of highly ordered nanostructures that enhance charge storage [246]. The development of advanced IL-based materials presents an opportunity for increased ion conductivities for many electrochemical applications [247,248]; however, to the best of our knowledge, the synthesis of these materials is not yet carried out on an industrial scale, presenting problems with their commercialisation. As demand for new battery materials increases, developments in the synthesis of these materials may speed up in response.…”