Dielectric properties of binary liquid systems at very dilute concentrations determined by using a stepwise dilution method

A stepwise dilution method to determine the dielectric constant at a frequency of 1 MHz has been developed and the dielectric properties of benzene, ethanol, 1-butanol, chlorobenzene, dioctyl succinate, and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in cyclohexane were determined at 298.15 K. From the precise measurements carried out for very dilute concentrations, it was found that there is a critical concentration for the threshold of solute-solute interactions at a mole fraction lower than 10−3. Apparent dipole moments for polar liquids were calculated as a function of mole fraction. The limiting dipole moments μ∞ for polar molecules were determined from the dielectric constants at mole fractions lower than the critical concentration of the solute-solute interactions by using the Debye and Frohlich equations. The value of μ∞ for chlorobenzene calculated by the Frohlich equation agreed very well with literature values determined for the vapor phase.