Effects of Pressure on Dielectric Relaxation in a Chlorinated Diphenyl

Data are presented on the dielectric properties of a commercial chlorinated diphenyl, Aroclor 1260, over a wide range of frequencies and temperatures, and also over a range of pressures up to 200 kg/cm2 at four fixed temperatures from 17 to 51°C. The data are compared with acoustical-relaxation data previously obtained, and with viscosity-temperature data for the same material. Similar data, from the literature, are evaluated for glycerol. The ratio η/τD is calculated over a range of temperatures for Aroclor 1260 and over a range of pressures for glycerol. The Aroclor 1260 data provide strong evidence against the applicability to this material of Debye's simple hydrodynamic model of a spherical dipole in a viscous medium. A distribution of relaxation times is observed, and it is pointed out that, while this may be due, in part, to the variety of molecules in the Aroclor, it may also be ascribed to the variety of configurations in the vicinity of each molecule, including various degrees of association. Several additional lines of research are suggested. The term ``piezopermittivity'' is proposed for the property of certain materials, such as the Aroclors, which results in large changes in permittivity with pressure. Possible applications of piezopermittivity are discussed.