Predicting the Mechanical Properties of Triblock Copolymer Gels

The goal of this project is to create an algorithm that predicts the stress-extension behavior of styrenic triblock copolymer gels. These gels are used in a variety of different applications ranging from model surgery and ballistics gels to bike seat cushions. It is crucial that the gel used for a given application exhibits the desired mechanical behavior. The gels we study are composed of styrenic ABA triblock copolymers, such as poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS), and aliphatic mineral oil. The copolymers form a physically-crosslinked network which explains the gel’s mechanical robustness. To characterize the mechanical behavior of these gels, we perform quasi-static tensile tests. The results of which are nonlinear, elastic stress-extension curves. We fit this data using the slip-tube network model, which serves as the structure of our algorithm. The algorithm allows us to analyze trends in experimental moduli values as functions of our input parameters (copolymer concentration, block fractions, and molecular weight). We compare these experimental trends to the theoretical equations that characterize the moduli, and we can determine the residual between them. The results of this are moduli correction factors, as well as the recognition that the copolymer bridging fraction is not constant, but changes with copolymer concentration. These rectifications to the slip-tube network model allow us to bridge the gap between experimental data and theory and as a result make more accurate predictions of stress-extension behavior for any formulation of styrenic ABA triblock copolymer gel.