Friction factor calculation in nanochannels comprising different wall hydrophobicities and superhydrophobic structures: Molecular dynamic simulations

A non-equilibrium molecular dynamics simulation was employed to evaluate the friction factor of water molecules confined in nanochannels composed of silicon surfaces. The investigation of water flow behavior was focused on two sets of cases. At first, two smooth silicon surfaces were used to create the wall of nanochannels. Simulation results indicated that for the studied cases, more hydrophilic walls led to higher Darcy-Weisbach friction factor of the confined water. In the second case, Nanometer-sized protrusions with the aligned and staggered nanopost arrangements were used to decorate the silicon surface to produce possibly superhydrophobic surfaces. Our results indicated that the friction factor in staggered nanopost arrangement was significantly larger than that of the aligned one. We found that for both nonopost arrangements, by increasing the Reynolds number and decreasing the percentage of pillar surface fraction, the friction factor decreased and the slip length increased. We found that employing a superhydrophobic surface in nanopost configuration, depending on pillar surface fraction, could lead to a lower friction factor than a hydrophobic surface obtained by a decrease in the wall hydrophilicity. We believe that our computational findings could shed light on the efficiency, economy improvement, and miniaturization of the nanofluidic devices.