Critical micelle concentration, surface, volumetric, and hydrodynamic properties of polyoxyethylenemonohexadecyl ethers

Abstract

Surface, volumetric, and hydrodynamic properties of polyoxyethylenemonohexadecyl ethers at and below the critical micelle concentration were examined. The critical micelle concentration ( C 0) of the polyoxyethylene surfactants decreased as the hydrophilic chain length increased. The areas per surfactant molecules at the air/water interface increased while the free energy of adsorption decreased as the polyoxyethylene chain length increased. The packing densities of the polyoxyethylene surfactants were constant indicating the random coiling of the hydrophilic groups. The hydration of the surfactants decreased as the ethylene oxide chain length increased varying from 1.34 to 3 water molecules per ethylene oxide unit. The relationship between intrinsic viscosity and molecular configuration below C 0 was examined in terms of the Debye-Bueche, Kirkwood-Riseman, Flory-Fox, and Peterlin hydrodynamic theories. The results show that polyoxyethylene surfactants are randomly coiled in aqueous solution.