Chapter 2 - Dynamic Surface Tension and Surfactant Mass Transfer Kinetics: Measurement Techniques and Analysis

Abstract

This chapter deals with measurement techniques and the analysis of the dynamic surface tension and surfactant mass transfer kinetics. Surfactants are often added to reduce the surface tension at liquid-gas interfaces in processes where interface is created on rapid timescales. This is the case in the deposition of inks in printing, the creation of thin films in the manufacture of photographic films, and in the application of paints, herbicides, and insecticides. In the formation of foams, a liquid-gas interface is created; in the formation of emulsions, a liquid-liquid interface is produced. The stability of foams or emulsions depends strongly on the interfacial energy of the system, and the stability of the thin-film lamellae, both of which are modified by the addition of surfactants. The evolution of the surface tension is determined by two issues: (1) the thermodynamic relationships between the surface tension, the surface concentration, and the concentration of surfactant in the bulk, and (2) the mass transfer rates of the surfactant through solution to the interface. The thermodynamic relationships relate the surface tension to the instantaneous surface concentration in systems far from equilibrium. The most commonly adopted thermodynamic model for the surface tension is the Frumkin model. This chapter briefly describes other surface tension models, and concludes with a discussion of methods that are commonly used to measure surface tension or to determine surfactant transport dynamics.