Non-ionic surface-active agents. Part VII. Solubility of benzoic acid in aqueous solutions of some monododecyl polyoxyalkanols

Abstract

Further study has been made of the solubility of benzoic acid in aqueous solutions of polyoxyalkanols of general formula (C₁₂H₂₅·[OCH₂·CH₂]_mOH)(I) where m= 2–12. The surfactants were prepared by methods giving materials of specific hydrophilic chain length and this was confirmed by gas chromatography. Lower members of the series (m= 2–6) had poor solubilising powers since addition of benzoic acid caused the aqueous solution to separate into two liquid phases, probably because the lower consolute temperature of the systems was depressed below 20°. Higher members (m= 7–12) were more effective and solid benzoic acid separated at the solubility limit. The results are compared with two models which have been used to describe the solvent properties of micellar solutions of non-ionic surfactants. It is concluded that the partition model is more satisfactory than the one in which benzoic acid is adsorbed at the interface of the ‘core-and-capsule’ within the micelles.