RELATIONSHIP BETWEEN OIL-WATER INTERFACIAL-TENSION AND OILY SOIL REMOVAL IN MIXED SURFACTANT SYSTEMS

Detergency of oily soil is a complex kinetic process that includes con tributions from the wash system physical properties, time and temperat ure of wash, and the hydrodynamic forces exerted during the wash proce ss. Generally, surfactant mixtures that exhibit a low oil-water interf acial tension are considered to provide superior oily soil detergency. In our investigations, we measured the oil-water interfacial tension for C12EO3/NaLAS and C12EO7/NaLAS blends as a function of temperature (18-80 degrees C) and time (0-60 min). The oil-water interfacial tensi on was found to decrease as a function of time for all blends containi ng nonionic surfactants, and this decline was most rapid for blends co ntaining a higher fraction of ethoxylated alcohol with less than 3 mol of ethylene oxide. It is proposed that the diffusion of this hydropho bic fraction into the oil phase leads to the measured decline in the o il-water interfacial tension. Also, due to this limitation, no general correlation of oil-water interfacial tension with oily soil removal w as observed. In view of these observations, it appears that the measur ement of the oil-water interfacial tension (using a spinning drop tens iometer) for solutions containing hydrophobic surfactants may give mis leading-results. (C) 1998 Academic Press.