Dynamic properties of adsorption layers of amphiphilic substances at fluid interfaces

Abstract

New experimental techniques as well as the foundation of the theoretical basis of the dynamic interfacial behaviour lead to much information on the dynamics of adsorption layers of surfactants at fluid/fluid interfaces. Surfactants at interfaces are characterized by a spectrum of relaxation processes.Where one of these relaxations is due to a simple mass transfer between interface and adjacent bulk phase in a laminar state without any barrier, the interpretation of many experimental data in the literature shows a confusing picture. One of the aims of the present review is to show how to perform measurements of the time dependence of interfacial tensions and to describe these data by a realistic mathematical model. Another topic is related to some dynamic properties of liquid interfaces, e.g. the flow of thin liquid films, the movement of bubbles and surface wave propagations. These processes are associated with the so-called “surface rheology”, which is strongly coupled with all lateral and vertical transport processes at the adsorption layer. Additional information about intermolecular forces and the structure of adsorption layers can also be obtained from rheological studies, especially from shear rheology in the case of mixtures of surfactants and macromolecules. The experimental and theoretical work is presented in an academic format but is also related to practical application of surfactants and the better understanding of complex processes in chemical technology, engineering and biotechnology.