In situ tribometry with real-time imaging for assessing durability and wear mechanisms of easy-to-clean coatings on glass for touchscreen substrates

Abstract

Touchscreens are now commonplace around the world, and easy-to-clean (ETC) coatings are integral in ensuring an enhanced usability and interactivity with these devices. In the present work, we evaluate the durability and study the wear mechanisms of a fluorine-containing easy-to-clean coating on glass using an in situ tribometer (TribTik). The TribTik is equipped with a microscope lens and camera system that allows one to image, in real time, the contact area between the glass substrate and the abrading counterpart. Through this unique combination, the instantaneous coefficient of friction and the contact area’s status can be monitored and correlated in situ. The in situ monitoring enables one to stop the abrasion cycles at critical stages of the wear process so that the morphology and composition of the wear tracks can be examined in an effort to understand the wear mechanisms of the ETC. We demonstrate that changes in the instantaneous coefficient of friction (COF) are correlated with changes in the in situ images. Critical stages of wear evolution are also identified via optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Raman analyses. The evolution of the ETC wear mechanism, from start to finish, was found to be described by the following sequence: (1) generation of unconsolidated debris, (2) formation of a layered tribofilm, (3) cracking of the tribofilm, and (4) general failure of the ETC and subsequent damage to the underlying glass substrate. Our study shows that, TribTik, a tribometry system with real-time imaging capability, is a powerful tool to characterize the tribological properties of coatings on touchscreens and/or display substrates.