Surface scientists have observed the surface charge at the interface between water and a remarkable variety of materials. See especially the paper by Zimmerman et al., and the recent spectroscopic work by Tian and Shen. References to many other important experiments may be found in our paper explaining the hydroxide's surface affinity. Though we believe we have the only viable explanation of the phenomenon, much is still not understood, and there is plenty of work still to do. Email me if you're interested in working on this project.
All ions constrain the polarisation fluctuations of nearby waters, and so reduce the relative permittivity of the solution (see figure below). The hydroxide ion reduces the relative permittivity of its aqueous solutions more than other small ions; it has a large dielectric decrement. This implies that hydroxides greatly suppress the collective dipole-moment fluctuations of nearby waters, and this leads to a dispersion force attracting the ion to a hydrophobic interface.
When the hydroxide ion is near an interface between water and a hydrophobe, the thermodynamic cost of 'broken' correlations is less than when the ion in in the bulk. The free energy of polarisation fluctuations is least when the hydroxide is near the interface.
This effect arises from correlations in the fluctuations of the waters' collective dipole moment. It is physically similar to electronic dispersion forces, and was studied for the case of only two molecules by Keesom, but this approach neglected the many-body correlations that amplify the effect in liquid water.
Textbooks commonly divide intermolecular forces into electrostatic, dispersion, and hydrogen bonding forces. Electrostatic interactions may be further divided into those between charges, or between various multipoles, both permanent and induced. The fluctuation force we describe fits into none of these categories. It most resembles the well-known electronic dispersion, but unlike its electronic relative, it is an entropic force, whose effects vary very differently with temperature.
There are many fascinating unexplained phenomena in atmospheric chemistry, biological chemistry, and surface science to explore, and we have the only theory that agrees with all the data on the surface affinities of hydroxides. We plan use our computer models of surface structure to study the workings of proteins and membranes, the rates of reactions and the structures of surfaces. There is also room for experiments on surface charges.
We know that this force makes the concentration of hydroxides within about 1 nm of a surface between ten thousand and a million times higher than in bulk water, and we have evidence suggesting that the same effect is present near proteins and biological membranes.