Short time dynamic interfacial tension as studied by the growing drop capillary pressure technique

For the characterisation of interfaces between two immiscible liquids, capillary pressure tensiometry is the most versatile method. To measure short time interfacial tensions it has to be applied under very dynamic conditions for which the following protocols have been developed: 1-continuously growing drop (CGD); 2-pre-aged growing drop (PGD); 3-stopped growing drop (SGD). The CGD is a procedure analogous to the well-known maximum bubble pressure tensiometry for liquid-gas interfaces, however, the processes of drop detachment and formation of the subsequent drop require a rather complex data analysis. For the PGD protocol based on a growing drop with an initially pre-established equilibrium adsorption layer, the complexities are less, but for higher surfactant concentrations it is not optimum. The SGD protocol provides a drop with a fresh surface and the dynamic interfacial tension can be monitored in the absence of hydrodynamic effects. All three protocols complement each other and provide a good set of data for dynamic interfacial tensions at short adsorption times.