Intrinsic slip on hydrophobic self-assembled monolayer coatings

The slippage of liquids over solid surfaces is receiving a growing interest for its potential applications to microfluidic devices. Hydrophobic coatings of smooth surfaces have been reported able to induce a significant slip length. A considerable debate is found in the literature, and a substantial scatter in the measured slip lengths, ranging from zero to few microns, exists. Here we discuss a detailed molecular dynamics simulation of liquid water flowing over a self-assembled-monolayer of octadecyltrichlorosilane. The data provide a value of the slip length in the range of 0.2-0.6 nm, smaller than the most recent value of 20 nm obtained by means of an accurately controlled experiment with the surface force apparatus. The discrepancy between experiments and simulations is discussed, commenting on the possible effect of surface imperfections.