DILATIONAL AND SHEAR RHEOLOGY OF ADSORPTION LAYERS AT LIQUID INTERFACES

Dynamic properties of interfaces are of increasing interest in science and in practice as they give insight into interactions and processes at interfaces rather than equilibrium properties. The general ideas on mechanical interfacial properties as an important part of dynamic pro perties were established long ago by Gibbs and Boussinesq. Now on the basis of new techniques, better experiments can be performed which all ow a more and more quantitative understanding. The mechanical behaviou r of interfaces, modified by soluble adsorption layers or insoluble mo nolayers of surfactants or polymers, is the subject of many actual stu dies. Computer-driven instruments using new sensors and very sophistic ated methodologies enable us to perform very complex and sensitive mea surements which were impossible until recently. Numerous studies of in terfacial shear and dilational rheology have been reported and use a l arge variety of techniques. Shear experiments are most useful for poly mer and mixed polymer-surfactant adsorption layers and insoluble monol ayers and give access to interaction forces in two-dimensional layers. Dilational interfacial properties however are most frequently studied for soluble adsorption layers of surfactants and mixtures of polymers and surfactants. This overview gives an introduction to the interfaci al rheology and discusses some specific theoretical aspects necessary to interpret experiments. Experimental techniques to perform shear and dilational experiments at liquid interfaces are summarised and only t he most recent developments are described in more detail. Examples are given to demonstrate how the experiments work and what output can be expected.