Decoupling of ionic conduction from structural dynamics in polymerized ionic liquids
Abstract
Polymerized ionic liquids (PolyILs) are a novel class of functional polymers that combine the unique physicochemical properties of molecular ionic liquids (e.g. wide electrochemical windows, negligible vapor pressures, and ionic conduction) with the outstanding mechanical characteristics of polymers. These materials are promising for a variety of applications including dye-sensitized solar cells, portable batteries, actuators, field-effect transistors and electrochromic devices. A major advantage of ionic liquids is the large variety of cations and anions available providing a possibility to design billions of chemically distinct materials with desirable properties for different uses. In PolyILs, one type of ion is covalently tethered onto the polymer matrix, only the counter-ions move freely in an electric field thereby contributing to charge transport. Thus, there is a possibility to select faster counter-ions to enhance ionic conductivity in this class of materials. However, a rational design strategy requires detailed fundamental understanding of the interplay between charge transport and structural dynamics in polymerized ionic liquids. Despite the promising prospects as ideal polymer electrolytes, the interplay between ion transport and structural (segmental) dynamics in PolyILs remains poorly understood. According to classical theories, the self-diffusion and ion transport in electrolytes are controlled by structural relaxation. These approaches predict similar temperature dependence for the dc conductivity and for the structural dynamics. Although this prediction has been shown to hold reasonably well for aprotic low molecular weight ionic liquids, it was recently found that it fails for PolyILs. The overarching goal of the proposed research is to unravel the mechanisms controlling charge transport and structural dynamics in polymerized ionic liquids. To achieve this goal, broadband dielectric spectroscopy and temperature modulated calorimetric techniques will be employed to investigate the impact of molecular parameters such as chemical structure, rigidity, ionic sizes as well as intermolecular interactions on the frequency and temperature dependence of the conductivity, dielectric function, diffusion coefficient, effective number density of the charge carriers, and the glass transition in polymerized ionic liquids. It is envisaged that the detailed fundamental understanding of the interplay between ion transport and dynamics gained in these studies will provide a basis for development of more efficient polymer electrolytes suitable for use in portable power sources and devices of direct relevance to the United States Army.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1710052
Entities
People
- Joshua R Sangoro
Organizations
- Army Contracting Command
- United States Army
- University of Tennessee