Critical Micelle Concentration of Poly(Oxy‐1,2‐Ethanediyl), α‐Nonyl Phenol‐ω‐Hydroxy Ethers (C9H19C6H4Ei=6,10.5,12,17.5) by Surface Equations of State

Abstract

AbstractThe analysis of surface tension variation versus surfactant concentration is the most usual method to estimate the critical micelle concentration (CMC). This parameter represents a fundamental thermodynamic boundary state where several surface properties, i.e. surface tension, surface pressure, surface concentration and surface coverage, simultaneously reach their limit values marking the conditions of the surface tension decrease. Thus the choice of the method used for CMC evaluation becomes of great importance, as the values depend on the principles from which the chosen method is derived. This paper presents CMC data from three surface equations of state: Gibbs, Langmuir and Volmer, modified to include the CMC among their constitutive parameters. Surface tension data of four nonyl phenol ethoxylates (6, 10.5, 12 and 17.5 ethylene oxide) along with ionic and non‐ionic surfactants from the literature were evaluated by the three surface equations of state; the following CMC × 107 values were obtained: for nonyl phenol 6 ethylene oxide 7.2, 7.2 and 6.8, for the 10.5 ethylene oxide 10, 12.4 and 9, for the 12 ethylene oxide 138.1, 147 and 137.4, and for the 17.5 ethylene oxide 4.9, 4.1 and 4.3 from Gibbs, Langmuir and Volmer equations respectively. These results compared with data from the literature, show the particular features of each equation, namely their predictive capabilities, and the thermodynamic parameters obtained besides the critical micelar concentration. It was found that for the critical micelle concentration determination in most cases Gibbs and Volmer models are equally satisfactory.