The above research illustrates the potential of NTs to exclude or conduct ions depending on diameter and environmental factors, but these studies are not selective to a particular ion type. In other words, cations will flow in one direction and anions in the opposite direction across these tubes under the influence of an applied field. In the following sections we outline research in which exclusive cation and anion selectivity is achieved. For example, Park et al58 designed a novel ion separator using a Yjunction CNT, illustrated in Figure 5. They demonstrated, using molecular dynamics, the ability to separate potassium and chloride ions from KCl solution by applying a negative and positive surface charge density to the two branches, respectively. Park et al suggest that a Y-junction CNT could be used as a fluidic component in complex fluid networks and nanoscale labon-chip applications.