Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The relative electric permittivity of liquid methylbenzene has been determined with an uncertainty of 0.01 % from measurements of the resonance frequency of the lowest order inductive-capacitance mode of a re-entrant cavity (J. Chem. Thermodyn. 2005, 37, 684 691) at temperatures between (290 and 406) K and pressures below 20 MPa and at T ) 297 K with a MicroElectricalMechanical System (MEMS) interdigitated comb capacitor. For the re-entrant cavity, the working equations were a combination of the expressions reported by Hamelin et al. (ReV. Sci. Instrum. 1998, 69, 255-260) and a function to account for dilation of the resonator vessel walls with pressure that was determined by calibration with methane (J. Chem. Eng. Data 2007, 52, 1660 1671). The results were represented by an empirical equation reported by Owen and Brinkley (Liq. Phys. ReV. 1943, 64, 32 36) analogous to the Tait equation (Br. J. Appl. Phys. 1967, 18, 965 977) with a standard (k ) 1) uncertainty of 0.33 %. The values reported by Mospik (J. Chem. Phys. 1969, 50, 2559 2569) differed from the interpolating equation by less than( 0.2 % at temperatures that overlap ours; extrapolating the smoothing expression to T ) 223 K, a temperature of 40 K below the lowest used for the measurements, provided values within ( 0.6 % of the data reported by Mospik. A parallel plate capacitor is described that was formed from interdigitated combs that were fabricated by the techniques of MEMS. This device has capacitances arising from fringing fields that contributed about 50 % to the total capacitance of about 3 pF. The fringing field was accommodated with a calibration with octane using the data of Scaife and Lyons (Proc. R. Soc. London A 1980, 370, 193 211, SUP 10031). The values of the relative permittivity of methylbenzene obtained with the MEMS at T ) 297 K and p less than 40 MPa deviated systematically from the smoothing equation based on the re-entrant cavity data by between -0.9 % at p ) 7 MPa and 0.5 % at p ) 42 MPa within about 5 times the estimated expanded (k ) 2) uncertainty of the measurements obtained with the MEMS.