Pile-up response of polymer thin films to static and dynamic loading

Polymer thin films are gaining significant attention these days because of its wide range of applications. Optoelectronics, microelectronics, touch screen panels, wrinkled surfaces, stimuli-responsive films, polymer micro and nanopillars for energy storage and contact lenses are some of the applications of these polymer thin films. In most of these applications, the measurement of mechanical properties of thin films is extremely critical. Pile-up is one of the parameters that significantly affect the measurement of mechanical properties during nanoindentation, nanoscratching, and nano-dynamic mechanical analysis (nano-DMA). These pile-up behavior for thin films are different from their bulk counterparts owing to their confinement in the growth direction. In this research work, static and dynamic loads were applied to study the pile-up response of polymer thin films and most importantly the related mechanisms. Influence of substrate, interface properties, film thickness, indenter shape and the magnitude of the load on the pile-up behaviour is investigated. Nanoindentation (at different loads starting from 40 μN to 500 μN), nanoscratch (at various depths ranging from 80 nm to 300 nm) and nano-DMA (at different frequency range starting from 10 Hz to 200 Hz) experiments were performed to pursue the objective. The effect of pile-up on the measured mechanical properties, such as, elastic modulus, hardness are estimated.