Physico-Chemical Properties of Polymers in Solutions and Suspensions, Surfactants in Solutions; Characterization of Fibres

In practice the used additives are polydisperse, and the result often difficult to interpret since it is never clear whether the effect is only the result of a subset of the used sample or if some subsets are more important with respect to their drag reducing efficiency. Although it is possible to produce a uniform sample of additives, it is not affordable. Since, as we will see later on, the drag reducing efficiency of the additives varies dramatically, it is evident that there is a need to characterize the additives by their physical and chemical properties as well as their geometry. However, it is not the intention of this presentation to completely characterize the additives but, rather, to discuss only properties which are relevant for describing the interaction of the additives with a turbulent flow. In other words, we will discuss the parameters which would also have to be considered in a dimensional analysis, such as the molecular weight and the aspect ratio of the additives, their extensibility and deformability. The main goal is to give information relevant for the additive-fluid interaction on a molecular level. Such information is essential to describe the competition between the bulk flow creating the distortion of the additives and the entropic restoring mechanism. Therefore a discussion of the self- and particle-particle interaction is omitted. The additives are thought to be present in a dilute concentration, a state which has to be defined for the various kinds of additives.