Dependence of the Dynamics of Spontaneous Imbibition into Carbon Nanotubes on the Strength of Molecular Interactions

We use molecular dynamics simulation to investigate the effect of the strength of water wall interaction on the spontaneous imbibition of water into a single-wall carbon nanotube at ambient conditions. Modeling the water carbon interactions with the Lennard-Jones potential, we find that water invades the tube only if the depth of the potential well epsilon and its cross section sigma are larger than some threshold values. Above the thresholds the speed of water uptake is an increasing function of the interaction parameters. We estimate the CNT wetting behavior from the speed enhancement factor for different LJ parameters. Far below the threshold and for very small values of the LJ parameters, water cannot penetrate the nanotube. There are intermediate states between the two limits in which water fills only a fraction of the nanotube's length, but the mass uptake varies quasi-periodically such that the net mass flow rate is zero. We also studied the time development of the electric dipole moment of the water column in the nanotube. The simulations indicate that, except for a small region next to the nanotube's entrance, the net electric dipole moment of water molecules inside the tube is negligible, irrespective of the wall water interaction strength.