Electrical impedance of the hydrophobic oil-water interface: contactless measurement

We have performed systematic contactless measurements aiming at the determination of the electrical impedance of an oil-water interface. The oil-water interface was formed within an insulin syringe tube due to the oil hydrophobicity. The measurement AC signal (0.1-300 kHz at 0.1 V) was capacitively coupled to the oil-water system through the syringe wall. The interface resistivity was estimated at ~2109m(assuming the interface as a slip layer with width ~ 10 nm) and was associated with hydroxide (OH–) ions, agreeing with existing reports. The resistivity was found to be independent on the signal frequency, which may indicate the nonpolarized nature of the hydrophobic interface. The present impedance spectroscopy is important for hydrophobic systems and may give an insight into the future nondestructive (contactless) investigation of the electrical properties of the lipid layer in the living cell membrane.