Experimental determination of the static permittivity of extremely thin liquid layers of water dependent on their thickness

Abstract

A new method for determining the static permittivity (dielectric constant) of extremely thin liquid interlayers is illustrated. A special condenser, which can be filled with a test liquid, is constructed. Both condenser plates — one planar, the other spherically curved — are made of vitreous carbon and are supplied with a high-grade politure. In order to adjust plate separation distances from 10 nm up to about some µm the planar plate can be easily shifted by a piezoelectric translation stage; the plate separation is monitored by an optical system supported by displacement transducers.

The measuring frequency was kept constant at 1 MHz. Water was chosen as the test liquid. At 19.8 °C thin water layers having thickness smaller than 0.3µm exhibit a decrease of the dielectric constant. The experimental data are consistent with a decay length α⁻¹ of the order of 1 nm which in view of the underlying crude model must be regarded as approximative.