Surface activity and thermodynamic of micellization and adsorption for isooctylphenol ethoxylates, phosphate esters and their mixtures with N-diethoxylated perfluorooctanamide

Three nonionic surfactants; p-isooctylphenol ethoxylates p-[i-OPE10], p-[i-OPE15], and p-[i-OPE20], were phosphorylated to produce three anionic phosphate ester surfactants. In addition, N-diethoxylated perfluorooctanamide (N-DEFOA) was also prepared. The surface and thermodynamic properties of the three types of surfactants and mixtures of the fluorocarbon surfactant (FC) with the hydrocarbon surfactants (HC) have been investigated. Surface tension as a function of concentration of the surfactant in aqueous solution was measured at 30, 40, 50 and 60 degrees C, using the spinning drop technique. From these measurements the critical micelle concentration (CMC), the surface tension at the CMC (gamma(CMC)), the maximum surface excess concentration (Gamma(max)), the minimum area per molecule at the aqueous solution/air interface (A(min)), and the effectiveness of surface tension reduction (pi(CMC)), were calculated. The thermodynamic parameters of micellization (Delta G(mic) Delta H-mic, Delta S-mic) and of adsorption (Delta G(ad), Delta H-ad, Delta S-ad) for these surfactants and their mixtures were also calculated. Structural effects on micellization, adsorption and effectiveness of surface tension reduction are discussed in terms of these parameters. The results show that the FC surfactant and its mixtures with HC surfactants enhance the efficiency in surface tension reduction and adsorption in the mixed monolayer at the aqueous solution/air interface, and also, reduce gamma(CMC) and the tendency towards micellization. (C) 2000 Elsevier Science B.V. All rights reserved.