Viscoelasticity of pore-spanning polymermembranes derived from giant polymersomes

Abstract

We show how the viscoelastic properties of membranes formed from poly(butadiene)-block-poly(ethylene oxide) (PB₁₃₀-b-PEO₆₆) block copolymers can be locally accessed by atomic force microscopy. Polymer membranes are spread on microstructured porous silicon substrates from PB₁₃₀-b-PEO₆₆ 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 cross-linked 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.