Some properties of an oil-soluble phosphated fatty alcohol ethoxylate

Abstract

Although phosphated hydrocarbon ethoxylates are claimed to have properties associated with the presence of both non-ionic and anionic groups in their molecules, a recent investigation of a phosphated nonylphenol ethoxylate demonstrated that the phosphate group had only a slight influence on the properties of this compound. The properties of an oil-soluble phosphated fatty alcohol ethoxylate of commercial origin has now been investigated. This material was substantially homogeneous, corresponding to a structure C9H19-(OCH2CH2)3-O-PO(OH)2—mol wt = 356 Although with considerable solubility in non-polar solvents, the compound has a slight solubility in water which is increased with increased pH, suggesting that the polar phosphate group has an influence on the properties of the compound. Measurement of the surface tension of aqueous solutions over a temperature range of 20–50° showed that there was an inflection point in the relation between cmc and temperature, behaviour typical of an anionic surfactant. As the pH is increased, the interfacial cross-sectional area of the molecule is progressively reduced at the air-water interface, but increased at the hexane-water interface. These results are discussed in terms of the orientation of the molecule at the interface, and the influence of a charged polar head group.