A Simple Model for the Dynamic Surface Tension of Polymer Solutions

Abstract

Surfactant and polymer solutions are usually used under conditions involving transient dynamic surfaces, and therefore the dynamic surface tension (DST) is important in many industrial and biological fields. In a previous paper, we proposed a new mechanical model for surfactant solutions based on the concept that surfactant molecules rotate during the process of approaching the equilibrium surface state, which is different from the conventional adsorption theory, and a simple expression of DST was obtained as a function of the surface age. In the present paper, we discussed another model for polymer solutions, which is based on the similar concept that polymers rotate during the process of approaching the equilibrium surface state. As a result, a simple expression of DST for polymer solutions was derived as a function of the surface age. The expression was compared with our experimental data, as well as with results reported by other authors, and it was found that they are in good agreement. Furthermore, the characteristic time, which is the only unknown parameter in the model, was shown to be correlated with the weight concentration of the solution regardless of the type of solution examined.