Tribological properties of commercial optical disks estimated from nanoindentation and scratch techniques

The structure of optical disks is a complex superposition of several layers with different objectives. The most external layer is usually designed with a protective purpose. When the scratch of the substrate occurs, the optical properties of the device decrease inducing a deficiency in the storage or access of data. Nowadays, the latest commercial optical disks exhibit protective coatings made of polymeric materials (copolymers, and polymeric matrix composite materials). The efficiency of these layers depends on a combination of several mechanical properties like hardness and Youngʹs modulus. In this work, a compositional and mechanical study was carried out on four commercial optical disks. Infrared (IR) analyses were performed to determine the composition of the external polymeric layers. Nanoindentation tests were done at different maximum loads to determine mechanical properties like hardness, H, and Youngʹs modulus, E, and their load dependence. The scratch resistance and the friction coefficients were determined from nanoscratch tests. Atomic force microscopy was used to estimate the scratch track. The H/E ratio seems to be one of the key factors to explain the wear resistance of the tested materials.