Molecular simulations have been carried out using the method of molecular dynamics to investigate the role of external electric fields on the ion mobility, drift velocity, and drift–diffusion rate of ions in aqueous electrolyte solutions. These properties are critical for a range of processes including electrodialysis, electro-deionization, electrophoresis, and electroosmosis. Our results show that external electric fields relax the hydrated ion structure at significantly larger time scales (between 300 and 800 ps), than most other relaxation processes in solutions (generally of the order of 1 ps). Previous studies that did not account for the much longer relaxation times did not observe this behavior for ions even with very high electric fields. External electric fields must also overcome several (at least two or more) activation energy barriers to significantly change the structure of hydrated ions. As a result, the dynamic behavior changes almost in bands as a function of electric field strengths, rather than linearly. Finally, the effect of the field is much less dramatic on water than the ions. Thus electric fields will be of more significance in processes that involve the transport of ions (such as electro-deionization) than the transport of water (electroosmosis).

The behaviour of cations in nanopores plays an important role in transport processes in the biological and industrial membranes, porous electrodes, ion channels, and nanomaterials in general. Molecular dynamics simulations have been carried out to study the selectivity mechanism of nanopores by studying the ion permeation events through non-charged carbon nanotubes (10,0) which have an effective diameter of 0.4374 nm. We have investigated pure NaCl, pure KCl and equimolar mixture of NaCl and KCl (50/50) aqueous solutions. Our results show that a membrane of uncharged nanotubes of the appropriate diameter can select K⁺ against Na⁺ without the presence of external electric field or surface charges. The key to the ion selectivity is that Na⁺-H₂O clusters are more stable than K⁺-H₂O clusters, and Na⁺ ions have higher desolvation energy than K⁺ ions. When both Na⁺ and K⁺ are present in the same solution, there is a competition between the two types of cations and the nanotubes select K⁺ over Na⁺.We also studied the effects of temperature and pressure to find the conditions, which permit Na⁺ to permeate through the nanotubes.