Tensile Properties of Ultrathin Bisphenol‑A Polycarbonate Films

The mechanical properties of bisphenol-A polycarbonate (BPA PC) have been extensively studied; however, measurement of these properties as sample dimensions approach the size scale of an individual polymer chain has been severely limited. Recently, we developed The Uniaxial Tensile Tester for Ultra-Thin films, enabling the direct measurement of the complete stress–strain relationship for the extension of ultrathin polymer films. We report measurements on the effect of thickness on the tensile properties of ultrathin BPA PC films. All PC thin films, regardless of thickness, showed clear shear banding deformations near a well-defined yield point, while the Young’s modulus and maximum stress decreased dramatically as the thickness decreased below the radius end-to-end distance for the polymer chains. In addition, we observed that the annealing history could be used to control the crystallization of PC thin films, leading to significant changes to the measured tensile properties. We propose a mechanism to explain these observed changes in the mechanical properties for ultrathin BPA PC films.