Interfacial aqueous solutions dielectric constant measurements using atomic force microscopy

The exchange of the volume of a region of the electric double layer of a mica surface immersed in aqueous solutions, with a dielectric constant ϵDL, by a nanosized radius tip, with a dielectric constant ϵTip, is responsible for the repulsion at large distances from the surface (starting at ∼100 nm, diffuse layer) and followed by an attraction when the tip is immersed in the inner layer (∼10 nm). The calculated dielectric constant as a function of the distance to the charged interface obtained by fitting the force versus distance curves, allows the mapping of the inner layer dielectric constant profiles with a nanometer resolution.