Wetting or Spreading in the Presence of Surfactants

In this chapter we consider the kinetics of spreading of surfactant solutions over hydrophobic and porons substrates. In spite of the wide use of these processes, currently we are not in the position to answer even basic questions in this area, such as how surfactant molecules are transferred in a vicinity of the three-phase contact line. 

In the case of aqueous surfactant solution, our knowledge of the behavior of the transition zone from the meniscus to thin films in front is very limited. Disjoining pressure isotherms in the presence of surfactants are investigated in the case of free liquid films [30], and much less is known in the case of liquid films on solid support. At the moment we cannot present a clear physical picture of the equilibrium of liquids or menisci ion the presence of surfactants. 

The most important problem of surfactant transfer in a vicinity of the three-phase contact line is to be investigated here. 

The situation is even less investigated in the case of simultaneous spreading and imbibition into porous substrate (Section 5.1). We present some theoretical and experimental investigations of the process (Section 5.1), which should be considered as a first step in this direction. 

In Section 5.6 we consider the much more theoretically understood process of flow caused by surface tension gradient (Maramgoni flow). We show that the flow caused by the point source of surfactant on the surface of thin aqueous film is caused by the surface tension gradient only. All other forces can be disregarded. This process recently became a powerful tool for investigation of the newly recognized phenomenon called superspreading. 

---

Dynamics of Wetting or Spreading in the Presence of Surfactants Results and Discussion... 

---