  Despite essentially identical crystallography and equilibrium structuring of
water, nanoscopic channels composed of hexagonal boron nitride and graphite
exhibit an order-of-magnitude difference in fluid slip. We investigate this
difference using molecular dynamics simulations, demonstrating that its origin
is in the distinct chemistries of the two materials. In particular, the
presence of polar bonds in hexagonal boron nitride, absent in graphite, leads
to Coulombic interactions between the polar water molecules and the wall, and
thus to an enhanced effective solid-liquid friction. We demonstrate that this
difference is manifested in the long wavelength, collective density
fluctuations in the confined water and accounts for the high conductivities of
graphitic channels. Based on this observation, we propose a novel scaling
relationship for the slip length, anticipated to be valid in the presence of
atomically smooth interfaces.
