  Using extensive room-temperature molecular dynamics simulations, we
investigate selective aqueous cation trapping and permeation in
graphene-embedded 18-crown-6 ether pores. We show that in the presence of
suspended water-immersed crown-porous graphene, K+ ions rapidly organize and
trap stably within the pores, in contrast with Na+ ions. As a result,
significant qualitative differences in permeation between ionic species arise.
The trapped ion occupancy and permeation behaviors are shown to be highly
voltage-tunable. Interestingly, we demonstrate the possibility of performing
conceptually straightforward ion-based logical operations resulting from
controllable membrane charging by the trapped ions. In addition, we show that
ionic transistors based on crown-porous graphene are possible, suggesting
utility in cascaded ion-based logic circuitry. Our results indicate that in
addition to numerous possible applications of graphene-embedded crown ether
nanopores, including deionization, ion sensing/sieving, and energy storage,
simple ion-based logical elements may prove promising as building blocks for
reliable nanofluidic computational devices.
