DIELECTRIC RADIOSPECTRA OF AQUEOUS-SOLUTIONS OF OXYETHYLATED NONIONIC SURFACTANTS

The dielectric permeability epsilon' and dielectric losses epsilon'' of aqueous solutions of oxyethylated isononylphenols (NOP) and a sample of OP-10 in the UHF range at temperatures from 275 to 313 K were investigated. The static dielectric permeability epsilon(s) of the surfactant solutions is described by the Maxwell and Wiener equations, developed for dispersed systems. The hydration numbers Z were estimated according to the data on the dispersion of the dielectric permeability epsilon of solutions of NOP-10, NOP-18, and OP-10 at 298 K. When the surfactant concentration was increased from 1 to 30% by weight, the value of Z changed from 5-6 to 2-3 water molecules per mole of ethylene oxide, which agrees with the data obtained by other methods. The activation energy of dielectric relaxation E(A) of aqueous solutions of NOP-10 and NOP-18 varied from 19.6 kJ/mole at 1% by weight surfactant to 25 kJ/mole at 20-30% by weight surfactant. The values obtained for E(A) are characteristic of the energy of formation of a hydrogen bond between the hydrogen atoms of water molecules and the ether atoms of the oxyethylene chains of the surfactants.