The behavior of hydronium and hydroxide ions at the water/alkane, water/vapor and
water/rigid wall interfaces was investigated by means of molecular dynamics simulations. All
these interfaces exhibit a strong affinity for hydronium, which is in agreement with
spectroscopic and low pH zeta-potential measurements. Except for the water/rigid wall
interface, which strongly structures water and weakly attracts OH-, none of the other
investigated interfaces shows an appreciable acumulation of hydroxide. This computational
result is at odds with the interpretation of higher pH zeta-potential and titration experiments,
however, it is supported by surface selective spectroscopies of the surface of water and
hydroxide solutions.