Paraelectric behavior and lamellar ordering in zwitterion-polymer blends

Abstract

We report the synthesis and dielectric characterization of a zwitterionic compound based on two common ionic liquid moieties. This compound can be blended with poly(methyl methacrylate) (PMMA) to form thin films. At high zwitterion concentrations, elevated temperatures, and low frequencies, the films exhibit behavior typical of electrochemical double layers, despite the absence of free ions. Capacitance values are in the range of 10 μF cm⁻² and do not depend on film thickness. At low temperatures, the films behave as linear dielectric materials with a dielectric constant of approximately 7. The transition between these two regimes is governed by a phase transition corresponding to the melting temperature of the zwitterion, as observed through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). X-ray diffraction (XRD) analysis suggests that at low temperatures and high concentrations, zwitterions adopt a lamellar structure characterized by strong antiparallel interactions between lamellae, which inhibit a strong paraelectric response. As the temperature increases, the compounds no longer exhibit phase separation and can adopt a parallel configuration, resulting in high capacitance paraelectric behavior. Overall, the zwitterionic compound reported here shows promising behavior that can be well-understood from its thermophysical and morphological properties.