Flexible zwitterions as soft dielectric materials

Zwitterions are neutral molecules with covalent linkage between a weak cation and anion. The structural separation between the charges causes zwitterions to have large dipole moments, and consequently a large dielectric constant, making them ideal candidates for numerous electronic applications like, supercapacitors, microwave components, thin-film transistors etc. We study a class of liquid zwitterions with varying linkage between the cation and anion using molecular dynamics simulations. The dielectric response of zwitterions at room temperature is of the order of microseconds, making efficient simulations crucial for our study. We accelerate the simulations by coarse-graining the molecular model of zwitterions while preserving essential chemical detail, and employing virtual-sites for the stiff parts of the molecules. We find two major contributors to the large dielectric constants these zwitterions: first, the alignment of molecules with the electric field, similar to the smaller rigid polar molecules. And second, the average separation between the cation and anion. The variable nature of dipole length is unique to flexible zwitterions as opposed to smaller rigid polar molecules.