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

Abstract

n-Alkyl polyoxyethylene glycol ethers (CiEO_j’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 C_i/EO_j’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 C_iEO_j’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.