The Surface Activity of Surfactants at Liquid Interfaces: The Role of CMC , Decrease in Surface Tension, HLB , Thermodynamic Adsorption Models

ABSTRACT 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 (), the maximum number of adsorbed surfactant molecules per interfacial area () 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.