The Static Dielectric Constant of Liquid Water Between 274 and 418 K Near the Saturated Vapor Pressure

Abstract

The complex dielectric constant (relative electric permittivity) $\varepsilon _{\text{r}} = \varepsilon ' - i\varepsilon ''$ of liquid water was redetermined in the temperature range 0°C<;t<145°C at pressures less than 440 kPa. In this work, ε_r was deduced from measurements of the resonant frequencies f _α of a novel, re-entrant, two-mode, radio-frequency resonator. The frequencies ranged from 23 to 84 MHz and were well within the low-frequency limit for ε′ because (2πf _ατ_max)²<5×10⁻⁵ where τ_max=1.8×10⁻¹¹ s is the maximum relaxation time of water under the conditions studied. The data for ε′ for two water samples differing in conductivity by a factor of 3.6 and for the two resonant modes differing in frequency by a factor of 2.6 were simultaneously fit by the polynomial function ε′(t)=87.9144−0.404399t+9.58726×10⁻⁴ t ²−1.32802×10⁻⁶ t ³ with a remarkably small residual standard deviation of 0.0055. The present data are consistent with previously published data; however, they are more precise and internally consistent. The present apparatus was also tested with cyclohexane and yielded the values ε′(t)=2.0551−0.00156t for 20°C<t<30°C, in excellent agreement with previously published values.