The innovation engine for new materials

My Linh Le

My Linh Le




Mount Holyoke College


Nicole Schauser

Faculty Sponsor(s): 

Ram Seshadri
Rachel Segalman

Faculty Sponsor's Department(s): 


Project Title: 

Effects of Polymer Dielectric Constant on the Molecular Structure and Ionic Conductivity of Polymeric Ionic Liquids

Project Description: 

Polymeric ionic liquids (PILs) have been intensively studied as an alternative for organic liquid battery electrolytes due to their enhanced mechanical strength, processability and safety. However, since the cationic species are either tethered to the polymer backbone or trapped in ionic aggregates within the polymer network, PILs have much lower ionic conductivity compared to organic liquids. To improve the conductivity of PILs, it is important to elucidate the relationship between the material’s molecular structure and its ionic conductivity. Previous computational results  suggest that the polymer dielectric constant plays a major role in ion dissociation, ionic aggregate structure and conductivity. We seek to verify this connection through the comparison of  PILs based on poly(ethylene oxide), with dielectric constant of ~ 6-8, and poly(butadiene), with dielectric constant of ~ 2-3. We also compare three different cations, Li+, Zn2+ and Cu2+, to examine the effect of charge density on aggregation and conductivity. Our preliminary results suggest that a higher dielectric constant polymer backbone leads to enhanced ionic conductivity of PILs, as measured via electrochemical impedance spectroscopy. Moreover, wide-angle X-ray scattering shows stronger ionic aggregation in the lower dielectric constant PIL with divalent cations, which is a likely cause for the reduced ionic conductivity. Future work includes further computational modeling of molecular structure for confirmation of this experimental observation, along with an accurate, reliable experimental method for determination the dielectric constant of the polymer backbone of these PILs.