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

非技术描述：硅酸盐玻璃在高科技光学工业和商品材料，如窗户，容器和纤维是至关重要的。这项研究是为了推进硅酸盐玻璃表面在环境条件下如何被摩擦接触损坏的机理知识。物理划痕或裂纹对玻璃物体实际强度的影响已经得到了广泛的研究，并且相对较好地理解；但是，在低负载条件下，由于摩擦接触而产生的化学或光学不可见的机械缺陷，对玻璃表面的影响知之甚少。阐明界面摩擦对硅酸盐玻璃力学和力学化学性能影响的科学突破可以促进玻璃技术的变革发展。今天，具有表面科学专业知识的研究人员在玻璃制造业中需求量很大。项目团队包括不同的学生（本科生和研究生）和博士后学者，并与校园组织合作。技术细节：通常通过测量硬度、断裂韧性或在相对锋利的压头施加的高接触压力下的开裂载荷/概率来研究由异物接触对玻璃的损害。虽然这些研究可以为极端接触压力条件下玻璃的力学响应提供物理见解，但它们不能解释在远低于压痕损伤阈值的机械载荷下，光滑和钝物体的界面摩擦导致的损伤模式。了解摩擦引起的表面损伤模式的内在因素（如玻璃的成分和热历史）和外在参数（如从周围环境中吸附的水分子）之间的相互作用是很重要的。正在研究的具体假设是：(a)摩擦引起的亚表面损伤可以在远低于压痕损伤阈值的接触应力下发生；(b)钠钙硅酸盐玻璃的机械化学磨损不仅受Na离子的影响，而且受混合改性离子（钠和钙）在吸附水分子存在下的相互作用的影响。后者是玻璃科学中尚未广泛研究的一种新型混合改性剂效应。这些假设是通过精心设计的控制实验和反应分子动力学模拟来研究的。亚表面损伤的松弛以及与其他二价离子（如镁）的相互作用引起了本项目的兴趣。总的来说，更好地理解控制接触引起的表面损伤过程的参数可以导致更好的玻璃设计，以提高硅酸盐玻璃材料的可用机械强度，以及具有低亚表面损伤和良好表面质量的高质量光学器件。研究动机和结果被整合到研究生课程中，由研究生和博士后研究员担任客座讲师。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.