Self Diffusion Dynamics and Viscoelasticity of Fluoresently Labeled Polymerized Ionic Liquids

Scaling relationships for viscosity and diffusion coefficient as a function of degree of polymerization (N) are well-characterized in neutral polymers. We have synthesized fluorescently-labeled polymerized ionic liquids (f-PILs) with a broad range of molecular weights to understand these relationships in dry, ionic polymers with a charge on every repeat unit. Fluorescence recovery after photobleaching (FRAP) is used to measure polymer self-diffusion coefficients (D ) using the post-bleached fluorescence images and fitting the intensity to a Gaussian profile over time. The zero-shear viscosity was measured via rheology. In the shortest f-PILs, the ionic interactions between imidazolium and bis(trifluoromethane sulfonamide) have little effect on extending the terminal regime. However, the terminal region did extend to lower frequencies as N increased. Interestingly, the wide-angle x-ray scattering shows an amorphous halo and anion-anion peak, but no longer range ionic aggregate peak which we assign as the origin of the rheological behavior. Scaling relationships with molecular weight will be discussed.