Mechanochemistry of Silicate Glass Surface: Mixed Modifier Effect on Resistance to Frictional Subsurface Damage

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NON-TECHNICAL DESCRIPTION: Silicate glasses are vital in high-tech optical industries and as commodity materials such as windows, containers, and fibers. This research is to advance mechanistic knowledge of how silicate glass surfaces are damaged by frictional contacts in ambient conditions. The impact of physical scratches or cracks on practical strengths of glass objects has been studied extensively and is relatively well understood; but in the case of chemical or optically-invisible mechanical defects made by frictional contacts under low load conditions, their impacts are far less understood for glass surfaces. Scientific breakthroughs in elucidating the impact of interfacial friction on mechanical and mechanochemical properties of silicate glasses can enable transformative growth in glass technologies. Today, researchers with surface science expertise are in high demand in glass manufacturing industries. The project team includes diverse students (at the undergraduate and graduate levels) and a postdoctoral scholar, and collaborates with on-campus organizations. TECHNICAL DETAILS: The damage to the glass by contact of foreign objects is typically studied by measuring hardness, fracture toughness, or cracking load/probability under high contact pressures applied with relatively sharp indenters. Although such studies can provide physical insights into mechanical responses of glass under extreme contact pressure conditions, they cannot explain the damage modes resulting from interfacial friction by a smooth and blunt object under a mechanical load far below the indentation damage threshold. Understanding the interplay between intrinsic factors (such as composition and thermal history of glass) and extrinsic parameters (such as water molecules adsorbed from surroundings) in friction-induced surface damage modes is important. The specific hypotheses being studied are: (a) friction-induced subsurface damage can occur at a contact stress far below indentation damage threshold and (b) the mechanochemical wear of soda lime silicate glass is governed not only by Na ions but by the interplay of mixed modifier ions (sodium and calcium) in the presence of adsorbed water molecules. The latter is a new type of mixed modifier effect that has not been examined extensively in glass science. These hypotheses are studied through carefully designed control experiments and reactive molecular dynamics simulations. The relaxation of subsurface damages and the interplay with other divalent ions (such as magnesium) hold interest to this project. Overall, a better understanding of parameters governing contact-induced surface damage processes can lead to better glass design for improved usable mechanical strength of silicate glass materials and well as high-quality optics with low sub-surface damage and good surface quality. The research motivation and outcome are integrated into a graduate course where the graduate student and postdoctoral researchers serve as guest lecturers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.