The Properties of Binary Mixtures of Ethoxylated Octyl Phenols with Ethoxylated Fluorinated Alkanols at the Water/Air Interface

Abstract

Surface tension measurements were carried out for systems containing binary mixtures of ethoxylated tert-octylphenols (with an average of 10 or 16 ethylene oxide groups—HC8PEO10 and HC8PEO16, respectively) with perfluorinated n-alcohol ethoxylates (fluoropentanol with an average of 10 ethylene oxide groups FC5EO10, and fluorohexanol with an average of 14 ethylene oxide groups FC6EO14). The obtained results and calculations indicate that fluorinated surfactants have the better efficiency and effectiveness in the reduction of surface tension of water that the hydrocarbonated alkyl phenol ethoxylates and that their mole fraction in the mixed monolayer at water–air interface for mixtures containing a 0.2 molar fraction of fluorinated surfactants in bulk phase is considerable higher than in the bulk phase. At concentrations of mixtures corresponding to saturated monolayer at water-air interface there is a synergetic effect in the reduction of $\gamma_{\rm LV}$ for a mixture of HC8PEO16 + FC5EO10 at a 0.2 molar fraction of HC8PEO16; however, taking into account the lowest value of the molecular interaction parameter for mixed micelles calculated on the basis of Rosen approach, the result is that the best synergism takes place for mixture of HC8PEO16 + FC6EO14 at a 0.2 molar fraction of HC8PEO16. Moreover, the ability of the mixed monolayer formation relative to the mixed micelle formation varies with the concentration and composition of the studied mixtures.

Graphical Abstract

The comparison between values of the free energy at water-air interface ($\Updelta G_{\min }^{\rm S}$) and the standard Gibbs energy of micellization, $\Updelta G_{\rm mic}^{0}$, for aqueous solutions of hydrocarbon (HC8PEO10, HC8PEO16) and fluorinated (FC6EO14, FC5EO10) surfactants and their two binary mixtures.