Solubilization of phenol in polyethoxylated nonionic micelles

Abstract

The solubilization of phenol in nonionic micelles of polyethoxylated nonylphenols having 20 and 30 ethylene oxide units was investigated by means of various techniques including solubilization, ultrafiltration, diffusion, ultraviolet spectroscopy, and viscosity experiments. From these measurements, the degree of partitioning of phenol into the micelles was investigated as a function of phenol concentration at three different surfactant concentrations for each system. The data obtained from ultrafiltration were treated as binding phenomena. The degree of partitioning of phenol into the micelles was found to be constant over the entire range of phenol concentrations in its solubilization region when the surfactant concentration was held constant. As the surfactant concentration was increased, the fraction of phenol partitioning into the micelles also increased. Diffusion and viscosity measurements revealed that the sizes of micelles at a fixed surfactant concentration do not change significantly with phenol addition. Moreover, from data analysis of binding phenomena of ultrafiltration, calculations showed that the maximum number of binding sites of phenol molecules per ethylene oxide unit was 0.19 at 25°C. These results suggest that phenol molecules are solubilized within the palisade layer of ethylene oxide units of nonionic micelles. The ultraviolet absorbance measurements, using hexaethylene oxide mono- n-dodecyl ether as surfactant, also support this result.