Differences between Dynamic and Equilibrium Surface Tension of Poly(oxyethylene)–poly(oxypropylene)–poly(oxyethylene) Block Copolymer Surfactants (Poloxamers P407, P237, and P338) in Aqueous Solution

Poloxamer surfactants are macromolecules with complex interfacial behavior. Although a number of studies of equilibrium surface tension have been published recently, there is little information on the diffusion of these large molecules to the air–liquid interface. Because most surfactants are used in dynamic systems, the diffusion to the surface can be critical in controlling performance. In this study a maximum bubble pressure method was used to study dynamic surface tension (DST) of Poloxamer P407, P237, and P338, at a range of bubble rates (surface age) and concentrations, at either 25 or 35°C. The DST did not change at the critical micelle concentration and also did not vary in the same manner as the equilibrium surface tension (EST) with respect to temperature. It was concluded that DST behavior of the surfactants was most closely related to the poly(oxyethylene) content and/or total molecular weight of the surfactants, whereas the micellization and hence the EST were more closely related to the poly(oxypropylene) content.