Uni-Directional Orientation of Ionic Domains in Block Copolymer Electrolytes for Anisotropic Ion Transport
In this talk, the technique of directed self-assembly of BCEs will be illustrated for engineering ionic domains perpendicular to electrode surfaces. The semi-conductor industry has adopted this technique for creating periodic, nano-patterned substrates.(7) In this approach, the surface interfacial energy was controlled using polymer brushes and solvent vapor annealing afforded phase separation between the blocks. Both perpendicular cylindrical and lamelle morphologies were prepared. Subtle reaction chemistries introduced the ionic groups selectively into one of the blocks without disrupting the block copolymer morphology. The specifics of the processing scheme will be elaborated on at the talk.
FTIR and x-ray photoelectron spectroscopy (XPS) confirmed the presence of ionic groups in the BCEs. Furthermore, XPS also demonstrated that the films participate in ion-exchange processes of the counterion. SEM and AFM determined the morphologies of the BCE structures. Figures 1a and 1b provide AFM images of a perpendicular fingerprint lamellae of poly(styrene-b-2-vinyl pyridine) (PSbP2VP) and poly(styrene-b-2-vinyl pyridinium iodide) (PSbP2VP+ I-). The images represent the block copolymer structures before and after introduction of ionic groups. In this work, ion conductivity measurements were made using electrochemical impedance spectroscopy (EIS) in thin films.
The talk will conclude with future research directions for the uni-directional orientation of BCEs that: i.) investigate the influence of BCE morphology, feature size, and defects on ionic conductivity and ii.) incorporating directed self-assembled BCEs into miniaturized, in-plane electrochemical devices (e.g., micro-batteries and micro-supercapacitors).
1. Y. A. Elabd and M. A. Hickner, Macromolecules, 44, 1 (2011).
2. W.-S. Young, W.-F. Kuan and T. H. Epps, III, Journal of Polymer Science, Part B: Polymer Physics, 52, 1 (2014).
3. N. Li and M. D. Guiver, Macromolecules, 47, 2175 (2014).
4. M. J. Park and N. P. Balsara, Macromolecules, 43, 292 (2010).
5. J. Li, K. Kamata, M. Komura, T. Yamada, H. Yoshida and T. Iyoda, Macromolecules, 40, 8125 (2007).
6. P. W. Majewski, M. Gopinadhan, W.-S. Jang, J. L. Lutkenhaus and C. O. Osuji, Journal of the American Chemical Society, 132, 17516 (2010).