Dielectric properties of silicone liquid films

The dielectric properties of silicone liquid films having the thickness of 5 to 10 μm have been measured in the viscosity range from 2 to 1000 CS, temperature range from -60°C to 150°C and frequency range from 30 to 10⁶ Hz. The results have shown that [1] the frequency dependence of relative dielectric loss factor ε_r" can be expressed by the relation ε_r" ∝ ω^-n, where the exponent n is smaller than unity and increases towards unity with increasing temperature, and [2] the value of ε_r" is independent of the liquid viscosity and field strength, and [3] the value of ε_r" of a thin liquid film exceeds that of a bulk form liquid by 1 or 2 orders of magnitude. These results suggest that the electronic hopping conduction contributes to the dielectric loss behavior of the liquid film. Hopping model of loss is applied to interpret our results. The consideration shows in good agreement with the obtained results that the frequency dependence of ε_r" can be qualitatively characterised by the hopping model of loss and the temperature dependence of the exponent n can be quantitatively determined by the ratio of the thickness of the liquid film and the thickness of ionic atmosphere (Debye-length of the screening charges) surrounding a hopping charge.