A new phase separation phenomenon in polymer and their application in proton conductive film

Significance 

The use of polymer materials has recently increased owing to their excellent properties and cost-efficiency. In particular, those with highly ordered structures have found application in the areas of solar cells, fuel cells and photonic devices. Presently, the highly ordered structures are fabricated by self-assembly of block copolymers with desired polymer architecture and chain length. However, due to the various challenges involved, researchers have been looking for alternative methods for fabricating the highly ordered structures and have identified the use of homopolymer and random copolymers as a promising solution. Unfortunately, the mechanisms underlying the formation of lamellar structures from self-assembled random copolymers have not been fully described. On the other hand, the nanophase separation between the side chain and the main chain have exhibited significant influence in the preparation of the lamellar structures especially by annealing under humid condition.

In a recently published literature, polymer electrolyte membrane materials have been used as a separator in the production of polymer electrolyte batteries and fuel cells. They are favorable for operation under humid conditions to achieve sufficient proton conduction. Additionally, the adsorbed water in these membranes forms a continuously connected water channel structure. Therefore, understanding the various types of structures formed and their influence through analysis of the scattering measurements is highly desirable.

Yamagata University researchers: Kazuki Ebata, Takanari Togashi and Jun Matsui in collaboration with Shunsuke Yamamoto and Masaya Mitsuishi from Tohoku University investigated the influence of humidity on the functionality of nanophase separation and proton conductive polymer electrolyte membrane. In particular, a high anisotropic proton conductive film was fabricated using highly ordered lamellar structure in a comb-shaped polymer. Their research work is currently published in the research journal, Journal of The Electrochemical Society.

Briefly, the research team commenced their work by synthesizing the proton conductive copolymer film from the decylacrylamide (DA) with 12-acrylamidododecanoic acid through free radical polymerization. Secondly, the polymer films were prepared on a solid substrate using the spin-coating method and the resulting structure analyzed using the X-ray diffraction technique. Furthermore, impedance measurements under both temperature- and humid controlled environment was used to evaluate the proton conductivities in both the in-plane and out-of-plane film direction. This eventually gave way for the analysis of the anisotropic film conductivity.

The authors observed featureless diffraction in the initial polymer film thus confirming its amorphous nature. However, annealing at 600C under 98% RH led to the conversion of the film structure from amorphous to highly oriented lamellar structure. Additionally, it was noted that the lamellar structures were formed between the main and side polymer chains due to nanophase separation. Even though the initial values of both the parallel and perpendicular proton conductivities were nearly the same, conductivity at the parallel direction increased while that at perpendicular direction decrease with an increase in the humidity. Therefore, the researchers successfully achieved the anisotropic conduction state through successful conductivity measurements. Generally, the developed anisotropic conductive film will advance the development of high-performance conduction devices.

About the author

Jun Matsui is currently a Professor in the Faculty of Science, Yamagata University, He received Ph. D from Tohoku University in 2003. Subsequently, he started his academic carrier as Assistant professor at Tohoku university and moved to Yamagata University in 2013 as associate professor and become a full professor in 2018. He received several awards, Young Science Awards, Miyagi Organization for Industry Promotion (2005), Awards for the Encouragement of Research in Polymer Science of the Society of Polymer Science, Japan (2006), Hatano Foundation Awards (2007), Tokin Awards (2009), Presentation award in “Element Block symposium, (2013). His current research interests include designing and processing of polymers, organic-inorganic hybrid materials for energy harvesting systems.

Reference

Ebata, K., Togashi, T., Yamamoto, S., Mitsuishi, M., & Matsui, J. (2019). Self Formed Anisotropic Proton Conductive Polymer Film by Nanophase Separation. Journal of The Electrochemical Society, 166(9), B3218-B3222.

Go To Journal of The Electrochemical Society

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