Development of Glassy Bicontinuous Cubic Liquid Crystals for Solid Proton-Conductive Materials

Significance Statement

Liquid-crystalline materials in bicontinuous cubic phases are of utmost interest due to their potential in developing a 3D continuous proton conduction pathway along an infinite periodic minimal surface. Previous studies showed it can be achieved by assembling amphiphilic zwitterions in the presence of an acid, bis(trifluoromethane)sulfonimide (HTf2N) to form a bicontinuous cubic structure. Ion change reaction between the two components to form ionic liquid-like ion pair is a key for the co-assembly.

In a recent article published in the journal, Advanced Materials, a new glassy liquid-crystalline material was produced, having ability to stabilize a bicontinuous cubic structure.

The authors used pyridinium-based amphiphilic zwitterions (PyZIn) and imide-type acids HA-R in equimolar reactions to form adducts exhibiting bicontinuous cubic liquid-crystalline phases. The resultant liquid crystals show glassification behavior upon cooling with keeping their 3D structures, which was characterized by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction measurements.

They found that a higher glass transition temperature was observed for the mixture of pyridinium-based zwitterion and HA-R acid when compared with HTf2N acid and as a result supports the fact that the freezing of the ionic domain comes before alkyl chains ordering when determining the phase behavior.

The glassy bicontinuous cubic structures were able to absorb water for a longer period without observing any change in their structures or morphology. This shows that other additives can be added to the glassy liquid crystals without change in their nanostructures.

With the use of HTf2N acid and amphiphilic zwitterion of PyZI16, crystallization that occurs during the continuous addition of water led to a change in morphology of the resultant liquid-crystalline nanostructures due to an outflow of the HTf2N acid to water phase. This result confirms that the glassification of the liquid crystals in reaction of the amphiphilic zwitterions and imide-type acid is far more preferable in keeping both the 3D molecular arrangements and assemblies of the nanostructures. Moreover, they confirmed the rapid increase in ionic conductivity of the glassy bicontinuous cubic structures due to arrangement of water molecules on the infinite periodic minimal surface which leads to the induction of proton hopping conduction.

The development of the glassy bicontinuous cubic liquid achieved in this study opens an avenue for induction of additives into the nanostructured liquid-crystalline materials without changing the 3D nanostructures.

Development of Glassy Bicontinuous Cubic Liquid Crystals for Solid Proton-Conductive Materials - Advances in Engineering

About The Author

Dr. Takahiro Ichikawa is an Associate Professor at the Department of Biotechnology and Life Science at Tokyo University of Agriculture and Technology. He received his PhD from The University of Tokyo in 2013 under the supervision of Professor Takashi Kato. His doctoral thesis title is “Functionalization of Ionic Bicontinuous Cubic Liquid Crystals”. Bicontinuous cubic liquid crystals are a class of liquid-crystalline materials that are known as those difficult to design. However, they have very mysterious and attractive nanostructures, which moved his heart and then he thought that he would like to challenge the development of functional bicontinuous cubic liquid crystals. He succeeded in overcoming the difficulty by employing ionic liquids, which are known as designer solvents, as a building block of liquid crystals. It should be pointed out that he carried out not only in the creation of these materials but also in the application of the obtained materials. For example, he found that 3D nanochannels of ionic bicontinuous cubic liquid crystals function as ion transporting pathway.

After he got a position as an assistant professor in Ohno-Nakamura laboratory in Tokyo University of Agriculture and Technology, his interest in bicontinuous cubic liquid crystals was retained. Taking some characteristics of specific ionic liquids into account, he succeeded in bringing some innovation in the design of functional bicontinuous cubic liquid crystals. And then He got an idea that the gyroid minimal surface should function as proton conduction pathways where proton transports through hopping mechanism. This concept has been investigated and some successful results have been obtained.

Reference

Kobayashi, T.1, Ichikawa, T.1,2, Kato, T.3, Ohno, H.1 Development of Glassy Bicontinuous Cubic Liquid Crystals for Solid Proton-Conductive Materials, Advanced Materials 29 (2017) 1604429.

Show Affiliations
  1. Department of Biotechnology, Tokyo University of Agriculture and Technology, Nakacho, Koganei, Tokyo, Japan.
  2. PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Japan.
  3. Department of Chemistry and Biotechnology, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan.

 

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