화학공학소재연구정보센터
Macromolecules, Vol.53, No.19, 8650-8662, 2020
Extreme Ductility in Freestanding Polystyrene Thin Films
Freestanding polystyrene thin films were found to reach elongations 2 orders of magnitude larger than what is found in bulk tests. We performed planar tensile testing at multiple strain rates using a push-to-pull based technique to obtain a quantitative stress-strain response of microtomed thin films with thicknesses ranging from 200 to 500 nm. In situ optical microscopy combined with postmortem transmission electron microscopy experiments were able to reveal the progression and microstructure of the deformation. It was found that the films undergo shear yielding and that crazing only occurs if the films are thermally annealed prior to testing. Regardless of thermal pretreatment, the microtomed thin films exhibited extreme ductility, which is at odds with previous reports on the mechanical properties of polystyrene thin films. The strain-softening amplitude was also found to directly depend upon the film thickness for unannealed thin films. Strain softening was not measured in thin films thermally annealed before quantitative testing. Comparisons to other relevant phenomena and current theoretical models are discussed in light of the extreme ductility that was found in what is a nominally brittle glassy polymer.