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作为日用品材料，如窗户、容器和纤维中是至关重要的。这项研究是为了提高硅酸盐玻璃表面在环境条件下如何因摩擦接触而损坏的机理知识。物理划痕或裂纹对玻璃物体实用强度的影响已被广泛研究，并被相对较好地理解；但在低载荷条件下摩擦接触造成的化学或光学不可见的机械缺陷的情况下，其对玻璃表面的影响了解得远远不够。在阐明界面摩擦对硅酸盐玻璃的机械和机械力化学性能的影响方面取得的科学突破可以使玻璃技术实现变革性的增长。今天，玻璃制造行业对具有表面科学专业知识的研究人员的需求很高。该项目团队包括不同的学生(本科生和研究生)和一名博士后学者，并与校园组织合作。技术细节：通常通过测量硬度、断裂韧性或高接触压力下的破裂载荷/概率来研究异物接触对玻璃造成的损害。虽然这些研究可以提供对玻璃在极端接触压力条件下的力学响应的物理洞察，但它们不能解释在远低于压痕损伤阈值的机械载荷下，光滑和钝化物体的界面摩擦导致的损伤模式。在摩擦引起的表面损伤模式中，了解内部因素(如玻璃的成分和热历史)和外部参数(如从环境中吸附的水分子)之间的相互作用是重要的。正在研究的具体假设是：(A)在远低于压痕损伤阈值的接触应力下，摩擦引起的亚表面损伤可以发生；(B)钠钙硅酸盐玻璃的机械力化学磨损不仅由Na离子控制，而且在吸附水分子存在的情况下，受混合改性剂离子(钠和钙)的相互作用影响。后者是一种新型的混合变质剂效应，在玻璃科学中还没有得到广泛的研究。这些假说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。亚表面损伤的松弛和与其他二价离子(如镁)的相互作用引起了这个项目的兴趣。总体而言，更好地了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，从而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。研究动机和成果被整合到研究生课程中，研究生和博士后研究人员担任客座讲师。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.