ABSTRACT
Unlike bulk water, water at aqueous interfaces exhibits a pro-
nounced anisotropic molecular ordering. The water density shows
a depletion in the interfacial region, to an extent depending on
ambient pressure and temperature [Mamatkulov et al. (2004)] and on the hydrophobicity of the surface [Sendner et al. (2009)]. Moreover, at soft surfaces, such as air-water interfaces, the density
increases monotonically, whereas at most solid surfaces, the water
molecules arrange in distinct layers, leading to an oscillating density
profile [Sedlmeier et al. (2008)]. Finally, vibrational spectroscopy experiments show that the water molecules in the interfacial region
are preferentially oriented with their dipole moments pointing
roughly along the surface plane at both air-water interfaces [Du
et al. (1993)] and quartz-water interfaces [Du et al. (1994a,b)]. For macroscopic solutes, this molecular structure strongly affects
both their static properties, such as double-layer capacitance, and
their dynamic behavior, such as electro-osmoticmobility and surface
conductance.
