The influence of geometry and wall character of pores on the permeation of ions and water through desalination membranes

The transport of water and ions across mimicked nanotube membranes with pseudo atoms is studied using molecular dynamics simulations under equilibrium conditions and hydrostatic pressure. Different pore surface properties are constructed by assigning partial charges on the sites of specified atoms to explore the influence of charges and polarity. The energetics of water and ion transports through the nanopores was calculated to evaluate their filterability to water. The simulation results show that the free energy barriers to water and ion conductions much depend on the charges at the pore entrance and the dipole within the pore. The membranes with hydrophobic pores and negatively charged entrances would be very efficient in the water transport and ion rejection. The charges and dipoles of the pore wall and the aligned dipoles of water molecules in the pore can create a significant force on ions.