Thermostat effect on water transport dynamics across CNT membranes

Whereas numerous experimental and simulation studies have been contributed to the investigation of fluid transport across membranes in the past decades, there is a significant discrepancy between experiments and simulations in the magnitude of fluid permeability and the degree of flow rate enhancement. Here, we show that one of the causes of the discrepancy is the variety of thermostating object, via which the temperature of fluid flow in non-equilibrium molecular simulations is controlled. By thermostating either the water system or the membrane material with Langevin method, we examine the temperatures of water flows in two types of membranes, the amounts of absorbed water molecules, fluid velocities, slip lengths and water fluxes. We show that thermostating the CNT membrane brings overall enhanced water flow than directly thermostating the water system. Moreover, increasing the temperature coupling time in the thermostat gives rise to an enhancement of water flux, while weakens the stability of system temperature. In addition to explaining the disparate simulation results on fluid transport in nanopores, this work provides guidelines for diagnosing the setting of NEMD simulations.