Adsorption of n-alkyl polyoxyethylene glycol ethers at liquid-vapour and liquid-liquid interfaces

n-Alkyl polyoxyethylene glycol ethers (CiEOj's) show peculiar adsorption properties at liquid interfaces. In fact, the partial hydrophobic character of the ethylene groups in the hydrophilic chain allows different orientations of adsorbed molecules. As a consequence, the usual adsorption models hardly predict the experimental observations, which calls for a more complex description. To this aim, a study on the adsorption properties of some CiEOj's is presented. The equilibrium data are interpreted according to a model assuming the partitioning, depending on the surface coverage, of the adsorbed molecules between two orientation states. Correspondingly, dynamic experiments are interpreted by a model considering both the transport of surfactant in the bulk phase by diffusion and the process of reorientation at the interface. These models provide a more accurate description of the experimental results for CiEOj's at the water-air interface. For adsorption dynamics at the liquid-liquid interface, the transfer of surfactant between the two phases must be explicitly considered.