Mechanical Properties of Ultra-thin Polycarbonate Films

Polycarbonate (PC) is a transparent, ductile polymer used in applications varying from water bottles to optical media to aircraft canopies. The mechanical properties of PC have been extensively studied; however, understanding how these properties change as sample dimensions approach the size scale of an individual polymer chain is severely limited. Recently, we have developed TUTTUT (The Uniaxial Tensile Tester for Ultra-Thin films), enabling the direct measurement of the complete stress-strain relationship for the extension of ultra-thin polymer films. We report measurements on the effect of thickness and annealing history on the tensile properties of PC ultra-thin films. All PC thin films, regardless of thickness, showed clear shear banding deformations near a well-defined yield point; however, the Young’s modulus and maximum tensile strength decreased dramatically as the thickness decreased below the average configurational size scale 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 an initial hypothesis to explain these observed changes in the mechanical properties for ultra-thin PC thin films.