PHASE-BEHAVIOR OF MONODISPERSE AND POLYDISPERSE ETHOXYLATED ALCOHOLS

Model polydisperse ethoxylated alcohols were prepared by the reaction of pure dodecanol with ethylene oxide. The patterns of phase behavior of the model polydisperse surfactants were directly compared with those of monodisperse ethoxylated alcohols in water and oil/water mixtures. The polydisperse surfactants are effectively less hydrophilic than monodisperse surfactants in pseudobinary mixtures with water since cloud points occur at lower temperatures. In pseudoternary mixtures with oil and water ( 50 50), the microemulsion phases occur at higher temperatures and thus polydisperse surfactants are effectively more hydrophilic than monodisperse surfactants. The differences are traced to the significant amounts of unreacted alcohol and ethoxylated alcohols with low levels of ethylene oxide within the polydisperse distribution. Quantitative analysis of the oil-rich and microemulsion phases within the three-phase region indicates that the partitioning of the polydisperse ethoxylated alcohols (which contain up to 20 components) is complex and cannot be simply described by assuming the mixture behaves as one or two pseudocomponents. © 1991.