Influence of nonionic surfactant additive on the properties of ionic surfactant solutions

Abstract

AbstractThe interaction of sodium dodecyl sulfate with a nonionic surfactant (a block copolymer of ethylene oxide and propylene oxide) has been investigated by the measurement of conductivity, surface tension and viscosity. The break point on the equivalent conductivity‐square root of concentration diagram which gives the critical micelle concentration (cmc) of sodium dodecyl sulfate became less definite by the addition of the nonionic surfactant, because of the decrease in conductivity below the cmc and increase above the cmc. The steep decrease in reduced viscosity took place in dilute concentration of sodium dodecyl sulfate solutions. In the surface tension vs. concentration diagram, the concentration at which the two linear portions of the curve intersect represents the cmc. The addition of nonionic surfactant decreases this crossed point of sodium dodecyl sulfate and finally obscures the crossed point. These reults are interpreted in terms of an interaction between sodium dodecyl sulfate and nonionic surfactant.