This paper presents measurements of the dielectric constant of HFC 134
a and HCFC 142b, as a function of pressure and temperature, in the tem
perature range from 200 to 300 K and pressures up to 20 MPa, using a d
irect capacitance method. The samples used had a stated purity of 99.8
and 99.9%, respectively. The values of the dielectric constant have a
precision of 0.01% and an accuracy of 0.1%. The data obtained were co
rrelated as a function of density and pressure. The theory developed b
y Vedam et al., based on the Eulerian strain, and the Kirkwood equatio
n for the variation of modified molar polarization with temperature an
d density were applied to analyze the data and to obtain the dipole mo
ment of both refrigerants in the liquid state.