Fundamental Mechanisms for Mechanochemical Behaviors of Glass Surfaces - An Integrated Experimental and Computational Approach

NON-TECHNICAL DESCRIPTION: The strength and wear resistance of glass are important properties for many consumer products including mobile phones, displays, automotive/aerospace windows, and for the safety of glass, in general. Although several strengthening processes such as tempering and ion-exchange are currently used in industry, the scientific foundations are not all fully understood. This limits further improvements in glass strength and reliability. The strength of glass is controlled by surface damage created in manufacturing and handling, as well as by the composition of the glass. This project engages in research to better understand the combined effects of mechanical stress and surface chemistry (called mechanochemistry). The scientific findings of this research are directly beneficial to glass manufacturers as well as users of glass in product development. TECHNICAL DETAILS: Mechanical and mechanochemical properties of silicate glass surfaces in ambient air are sensitive to alkali ion leaching and its exchange with hydrous species (hydroxyl or water). This research hypothesizes that interfacial shear or mechanical deformation causes local distortion of the silicate network surrounding the hydrous species such that the distance between the bridging oxygen of the Si-O-Si network and the hydrous species becomes shorter than the critical length needed to induce hydrolysis of the Si-O-Si network. This hypothesis is relevant to several important questions that are outstanding in glass science such as stress-induced transport of sodium ions and the catalytic effects of metal ions on hydrolysis of glass network. While existing stress corrosion theory can explain crack growth under an applied tensile stress, it cannot fully explain the chemical reactivity of confined water in contact with glass under both compressive and shear stress. This project employs density functional theory (DFT) and molecular dynamics (MD) simulations with reactive force fields (ReaxFF) to study the key hypothesis and related questions, and theoretical calculation results are tested and validated experimentally using state-of-the-art surface analysis techniques. This project educates undergraduate and graduate students in the engineering and science of materials with a focus on glass and its strength. The research team recruits students from underrepresented groups to work on the project. All students benefit from participation activities associated with various interdisciplinary materials research activities at the Materials Research Institute (MRI) and Material Computation Center (MCC) at Penn State. The team offers computational data to the Nanohub and the Knowledgebase of Interatomic Models (OpenKim) websites, so that their user-base can access these materials for future force field development and validation projects. Selected examples of the ReaxFF and DFT simulations and surface analysis results are integrated in two existing graduate courses.