Kelvin Probe Method to Evaluate Polarization Properties of Liquids

The polarization behavior analysis within dielectric materials is crucial for electronics. Here, we reconsidered the Kelvin probe (KP) technique, a widely used method for determining the work function and surface potential of solid materials, for assessing the polarization properties of deformable materials. Unlike impedance spectroscopy (IS), the KP technique measures displacement current by modulating the electrode spacing, rather than electrode potential. By phase-separating KP signal into displacement current and its delayed component (actual current), the KP method is expected to selectively measure polarization properties within the bulk, as the potential drop in the bulk and interface remains constant. We achieved precise phase separation of the KP signal using an optical lever signal synchronized with the electrode vibration as the reference for the lock-in amplifier. The complex dielectric constants ε_{r, KP}^* and ε_{r, IS}^* of liquid samples were measured by KP and IS measurement, respectively. For nonpolar octane, ε_{r, KP}^* was almost equal to ε_{r, IS}^*. Alternatively, for polar 1-octanol and 2-octanol, ε_{r, KP}^* was smaller than ε_{r, IS}^*. We also estimated that the bulk potential drop in 1-octanol and 2-octanol is approximately one-tenth of the total potential drop. The proposed approach offers a novel method for evaluating energy diagrams and provides insights into the polarization mechanisms of deformable materials.