Equilibrium Adsorption Properties of Single and Mixed Surfactant Solutions

SINTECH Surface and Interface Technology, Volmerstrasse 5-7, D-12489 Berlin, Germany 3.1 Introduction 

In this chapter, we present systematised experimental results for equilibrium surface (in some cases interfacial) tensions for several homologous series of non-ionic and ionic surfactants. In contrast to what is generally believed to be trivial, we paid large attention to the selection of reliable experimental equilibrium data. Two main principles were employed here  

The related questions were extensively discussed in the monograph [17]. We believe that all data obtained in our laboratories are in full compliance with these requirements. Also, the conditions of equilibrium establishment were controlled in studies performed in the groups ofJoos, Lucassen-Reynders, Lin and other authors. For surfactants with high adsorption activity, e.g., oxyethylated alcohols or ethers, the concentration in the solution is low, and the time necessary to attain the equilibrium is usually tens of hours. Therefore the data published for such systems are not necessarily equilibrium ones. To illustrate this, we present below some results published in the literature, which do not satisfy the requirement (ii). Hence, it is no surprise that these data do not agree with the general trends observed. 

The structure of this chapter is as follows. First, the results obtained for individual surfactant solutions are presented, which are preceded, for the sake of convenience, by a summary of the main equations corresponding to the various theoretical models discussed in Chapter 2. The software used for fitting the models to experimental data will be described in Chapter 7. Then, surfactant mixtures are considered with a number of experimental and theoretical examples. A summary of the main theoretical equations for mixtures of ionic and non-ionic surfactants (the corresponding fitting software again is described in Chapter 7). Also some approximate theoretical models for the mixture of two or more surfactants is presented and compared with experimental results. 

---

Equilibrium Adsorption Properties of Single and Mixed Surfactant Solutions... 

---