Molecular reorientation in the adsorption of some CiEj at the water-air interface

As demonstrated by some recent works the adsorption properties of some n-alkyl poly-oxyethylene glycol ethers can be explained by a model assuming the co-existence of different orientation states for the adsorbed molecules. In the present paper, with the aim of giving complete evidence of the above, the adsorption isotherms and the adsorption kinetics of some n-decyl and dodecyl poly-oxytheylene glycol ethers (C10E8, C10E5, C10E4, C12E5, C12E8) at water/air interface have been studied by using the pendant drop technique. The data have been interpreted with a model considering the possibility of two orientation states for adsorbed molecules. The results of this study show that the model accurately describes both the equilibrium and dynamic adsorption behaviour of these molecules and that adsorption at water/air is controlled by diffusion. Moreover, the analysis of the best fit isotherm parameters of homologue molecules gives interesting information about the configuration of the adsorption layer. (C) 1999 Elsevier Science B.V. All rights reserved.