Surface activity of alcohols ethoxylates at the n-heptane/water interface

The interfacial activity of alcohols ethoxylates CiEOj (where C = methylene or methyl, EO = oxyethylene, i = 6–10 and j = 3–6) at the aqueous phase/heptane interface was studied. The data analysis shows that their adsorption behavior depend on the structure of the surfactant. The equilibrium adsorption isotherms were simulated taking into account the possibility that molecules could reorientate at the interface and therefore adsorb in two different states. Perfect agreement was observed between experimental and theoretical points. The effectiveness and efficiency of adsorption are also a function of the alkyl chain length i and the number of ethylene oxide groups j. A linear relationship between the standard free energy of adsorption and j was found. From the slope the contribution of each EO group to the free energy change was calculated.