Microwave dielectric losses of n-alkanes

Abstract

Dielectric losses (tan δ=ε″/ε′) and permittivities (ε′) of the n-alkanes from C₅ to C₁₄ have been measured using waveguide bridges at 8.855 and 34.82 GHz and using helical cavities at 10.0 and 35.0 GHz. The waveguide bridge measurements spanned a temperature range from +25 to –40 °C whilst the cavity measurements were restricted to ambient laboratory temperature. The limits of accuracy achieved were ±0.1% in ε′ and ±1% in tan δ. Comparisons with previous work enable an analysis to be made of the losses in terms of a relaxation process with a Fröhlich distribution of relaxation times. The principal relaxation time at 20 °C rises from 1.6 ps for C₅ to 10.6 ps for C₁₄ whilst the effective dipole moment rises from 0.071 to 0.082 D.