For all applications in which interfaces play a significant role, surface-active agents (surfactants) can play an essential role. The selection of the most suitable surfactant is essential but it is not a simple task. Depending on the type of applications, a certain surface coverage by surfactant molecules or a reduction in surface tension down to a defined value is required. Moreover, the formation of micelles above a certain concentration in a solution can be essential for the optimized application of a surfactant. Hence, the classification of surfactants according to their surface activity is necessary and has to take into account a variety of characteristic parameters. This can be the critical micelle concentration (CMC), the corresponding surface tension (훾CMC), the maximum number of adsorbed surfactant molecules per interfacial area (훤 ∞) or the concentration required to reduce the surface tension by a certain amount. Different interfacial parameters are discussed with respect to their application and possible interrelations between these parameters are analyzed.
