Anomalous dielectric response of very small quantities of virgin, aged and failed silicone oil

A technique is described for making dielectric spectroscopy measurements of very small quantities (<1 μl) of oil. The technique utilises surface tension to hold the oil between the plates of a capacitor, the inter-electrode distance being controlled by a micrometer. Breakdown strength can also be estimated using this technique. Three samples of silicone oil, used in cable sealing ends, were tested: virgin, used and failed. A major component in the frequency dependent impedance had the form Z(ω) = B(1-b(iω)^1-p). This component was interpreted in terms of a fractal percolation model, and the anomalous thickness dependence predicted by the model verified by varying the inter-electrode distance. The difference observed for the three different samples indicate that conducting contaminants are responsible for the percolation system.