CONCENTRATION AND TEMPERATURE EFFECTS ON AGGREGATION, CLOUDING AND ADSORPTION OF A POLYDISPERSE NONIONIC SURFACTANT IN AQUEOUS-SOLUTION

Aqueous solutions of 1-octanol polyoxyethylene glycol monoether with an average of 4.5 ethylene oxide units per molecule were subject to surface-tension and cloud-point measurements at temperatures ranging from 26 to 67-degrees-C. The former data were used to estimate values for the critical micelle concentration, space requirement for surfactants at the air/water interface as well as enthalpy and free energy of micellization for the polydisperse surfactant. Derived data were found to compare well with similar data for chemically closely related pure homologues, and this was taken to indicate close to ideal solute-solute interactions. The same solutions were also made the subjects of ultrafiltration using hydrophilic membranes. Temperature-dependent permeation ratios and flux rates suggested the occurrence of adsorption-induced excess permeation of surfactant at elevated temperatures below the lower critical temperature (LCT). Above the LCT, increasing phase separation resulted in very low permeation ratios, indicative of low aqueous surfactant concentration under phase-separation conditions. Results of permeation data for individual homologues were discussed in terms of models for temperature-induced adsorption and were also compared with results using other techniques reported recently in the literature.