Interfacial Tension Errors from the Cohen and Carriere Analysis of Imbedded Fiber Retraction

Immiscible polymers are often blended together to create new materials with desired properties. Knowledge of the interfacial tension between the immiscible polymers is important when designing such blending processes. Traditional methods of measuring the interfacial tension between low molecular weight fluids, e.g., the pendant or sessile drop method, the Wilhelmy balance, and the spinning drop method, do not work well for molten polymers because their high viscosity requires unacceptably long times for equilibration. Therefore, “dynamic” methods, which use the kinetics of interfacial tension-driven motion to obtain the interfacial tension, have been devised for polymers.1-6 One such method, the imbedded fiber retraction method, is the subject of this paper. The purpose is to demonstrate that the Cohen and Carriere (CC) model1,2 that is commonly used to analyze fiber retraction experiments can cause large errors in interfacial tension, whereas an alternate analysis by Tjahjadi, Ottino, and Stone (TOS)7 gives reliable interfacial tension values. A notable feature of our experimental approach is that the fiber retraction experiments are benchmarked rigorously: we are able to measure the equilibrium interfacial tension in the same experiment as the fiber retraction.