Zwitterions Raise the Dielectric Constant of Soft Materials

Materials exhibiting high dielectric constants (epsilon(s)) are critical for energy storage and actuators. A successful approach to increase epsilon(s) is to incorporate polar additives (with high epsilon(s)) but controlling the resulting dispersion state is difficult. Here, we show that significant epsilon(s) increases are realized by adding zwitterions, which are small molecules with a cation and an anion separated by covalent bonds. The increase in epsilon(s) with zwitterion addition is attributed to the large molecular dipole of zwitterions, ranging from 35 to 41 D, as experimentally quantified and confirmed using density functional theory. At elevated zwitterion concentration in an ethylene glycol medium, there is a nonlinear increase of epsilon(s) 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 es in soft materials.