Viscoelasticity of pore-spanning polymer membranes derived from giant polymersomes

We show how the viscoelastic properties of membranes formed from poly(butadiene)-block-poly(ethylene oxide) (PB(130)-b-PEO(66)) block copolymers can be locally accessed by atomic force microscopy. Polymer membranes are spread on microstructured porous silicon substrates from PB(130)-b-PEO(66) vesicles by decreasing the osmotic pressure of the solution. Local viscoelastic properties of the pore-spanning polymer membranes were obtained from site-specific indentation experiments. Elastic moduli of these membranes were in the order of few MPa, while the elastic moduli of crosslinked membranes considerably increased to few GPa. Furthermore, the energy dissipation and velocity dependence of the hysteresis between indentation and relaxation were quantified and compared with a modified Kelvin-Voigt model. Relaxation times were in the order of hundreds of milliseconds explaining why the stiffness of the membrane increases with increasing indentation velocity.