Interfacial Water Dielectric Constant in the Parallel Direction to Its Surface: A Measuring Technique

The dielectric constant of interfacial water was recently measured in the normal direction to the water surface; this study showed a significant reduction to a value as low as ε ∼3. Here, a technique that measures parallel to the water surface dielectric constant is described. An asymmetric arrangement of electrodes results in a configuration in which surface and bulk charging effects are separated. The water surface is responsible for the initial fast charge rearrangement. Parallel to the water surface, values as low as ε ≈ 35-40 were measured in agreement with models that show that this ∼50% reduction is associated with the interfacial water confined structure.