DLVO (Derjaguin–Landau–Verwey–Overbeek) theory and solvation forces between mica surfaces in polar and hydrogen-bonding liquids

Abstract

The force as a function of separation has been measured between molecularly smooth mica surfaces immersed in acetone and methanol containing varying amounts of electrolyte. At long range (≳ 5 nm) the measured force is the sum of an electrostatic double-layer repulsion, calculated from solutions to the non-linear Poisson–Boltzmann equation, and an attractive van der Waals force, computed from Lifshitz theory. At smaller surface separations there are oscillatory solvation forces similar to those found in non-polar liquids. The occurrence of hydrogen bonding in methanol is not seen to have any marked effect on the forces. To a first approximation the solvation force and double-layer force are additive in both acetone and methanol. It is concluded that the DLVO (Derjaguin–Landau–Verwey–Overbeek) theory provides an accurate description of the forces at long range in polar, non-aqueous liquids but that, as for non-polar liquids, the continuum van der Waals force is replaced by a solvation force at small surface separations.