Zwitterions Raise the Dielectric Constant of Soft Materials

Materials exhibiting high dielectric constants (εs) are critical for energy storage and actuators. A successful approach to increase εs by incorporating polar additives (with high εs) but controlling the resulting dispersion state is difficult. Here, we show that significant εs increases are realized by adding zwitterions, which are small molecules with a cation and an anion separated by covalent bonds. The increase in εs with zwitterion addition is attributed to the large molecular dipole of zwitterions, ranging from 35 to 41 Debye, as experimentally quantified, and confirmed using density functional theory. At elevated zwitterion concentration in an ethylene glycol medium, there is a non-linear increase of εs that eventually saturates due to the strong Coulombic interactions between zwitterions. The presented work provides a fundamental molecular understanding of why zwitterions are effective additives in boosting ε_s in soft materials.