Abstract
Abstract Ultrafiltration has been used to study binary anionic-nonionic surfactant mixtures. Micellar composition and CMC are reported for mixtures of decyl benzene sulfonate with nonyl phenol ethoxylates having average ethylene oxide chain lengths of 10, 20, and 50 and for mixtures of decyl, undecyl, and dodecyl benzene sulfonate with a nonyl phenol ethoxylate with an ethylene oxide chain length of 50. The regular solution theory (RST) approximation which has been used to characterize these mixtures is determined to be inadequate. A new theory is proposed which accounts for the excess entropy due to two effects: (1) nonrandom arrangements in the mixed-micelle and (2) conformational entropy changes in the polyethylene oxide chains. Good agreement with the data are obtained when the excess entropy is taken into account.
Published Version
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