(193bb) Formation/Dissolution of Silver Filaments through an Ionic Liquid-Polymer Electrolyte Composite

Zhongmou Chao ¹; Garrison Crouch ²; Donghoon Han ²; Paul Bohn ^2,3; David B. Go ^2,4; Susan Fullerton-Shirey ¹

1, Dept. of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA

2, Dept. of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN

3, Dept. of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN

4, Dept. of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN

Metamaterials with optical properties that can be tuned on demand would have applications in multiple areas including renewable energy and war fighter materials. One approach to develop these reconfigurable materials is to create and destroy conductive nanofilaments in well-defined locations within a dielectric film. It has been shown previously that densely packed nanofilaments embedded in a dielectric can give rise to strong anisotropy in optical properties. The interaction with light could be further tuned by precise control of the filament formation/dissolution kinetics, which would enable engineering the optical properties over well-defined time and spatial scales. In this study, a conductive AFM is used to electrochemically form nanoscale conductive filaments in a polyethylene glycol diacrylate (PEGDA)-based electrolyte blended with ionic liquid (IL) and silver salt. Filament formation and dissolution kinetics are measured at hundreds of spatially distinct points with the film for each electrolyte composition to unravel how the kinetics are related to spatial inhomogeneities in the electrolyte. Initial filament formation occurs on timescales that are 1000x longer than dissolution, which is reasonable since initial formation requires the electrochemical deposition of the entire filament while dissolution simply requires dissolving a few silver atoms to disconnect the filament. We find that the polymer/ionic liquid/salt film with the largest crystal fraction and the largest modulus (~4.8 GPa) also has the fastest filament formation/dissolution kinetics. This result is unexpected because fast ion transport is typically associated with fast segmental relaxation of the polymer host, and therefore a low crystal fraction. The results indicate that ion mobility in this system is likely governed more by the local polymer structure than by PEGDA chain mobility, thus creating an opportunity to tune the filament kinetics, and therefore the optical properties, by tuning the structure of the polymer.

Acknowledgement: This worked was supported by the Defense Advanced Research Projects Agency (DARPA) Atoms to Products (A2P) program, grant #FA8650-15-C-7546.