Molecular Weight Dependence of Polymersome Membrane Structure, Elasticity, and Stability

Vesicles prepared in water from a series of diblock copolymers“polymersomes”are physically characterized. With increasing molecular weight M̄n, the hydrophobic core thickness for self-assembled bilayers of poly(ethylene oxide)−polybutadiene increases up to ∼20 nm, which is considerably greater than any previously studied lipid or polymersome system. Micromanipulation of vesicles demonstrates an interface-dominated elasticity that is independent of M̄n. Furthermore, membrane stability as defined by the maximal areal strain increases with M̄n, approaching a universal limit predicted by mean-field ideas and set by the interfacial tension. Nonlinear responses and memory effects also emerge with increasing M̄n, indicating the onset of chain entanglements at higher M̄n. The results highlight the interfacial limits and transitions to bulk responses of self-assemblies.