RUI: Dynamic Light Scattering Test of Bond Model Predictions for the Dynamics of Network-forming Liquids near the Glass Transition

技术摘要无定形固相原则上是所有液体所特有的，尽管一些液体在冷却时有结晶的倾向。然而，在不同的材料中，液体在凝固前变稠的方式是非常不同的。过去的研究已经证明，过冷的玻璃形成液体的动力学与其化学结构和热力学性质之间存在明显的联系，这种联系被称为“脆性”。在这个项目中，动态光散射、拉曼光谱和差示扫描量热法被应用于探索网络形成系统中产生的简单结构变化如何直接影响液体动力学。这一结果将对现有的热力学模型(邦德模型)进行精确的检验。这项工作将由提供实践研究经验的研究生和本科生进行，以加强他们的科学教育。非技术摘要技术靠开发材料的新特性而蓬勃发展。其中，玻璃材料具有独特的机械、光学和电学特性，对许多最先进的设备具有重要意义。然而，为了实现它们的潜力，玻璃材料必须从液态凝固而不发生结晶。这就需要了解液体到玻璃的转变，特别是了解液体的化学结构如何影响增稠过程本身。在这个项目中，玻璃形成液体散射的可见光被用来在微观水平上监测这种增厚过程。将研究一系列玻璃形成液体，其中化学结构可以通过增加或减少液体中存在的平均化学键数量来系统地改变。随着结构的每一次修改，液体的动力学性质的相应变化将被评估，以检验基于存在的平均键数的简单模型的预测。研究生和本科生将进行这项研究，作为培养下一代专业科学家的手段。

Technical AbstractThe amorphous solid phase is, in principle, endemic to all liquids despite a propensity for some liquids to crystallize when cooled. However, the manner in which a liquid thickens in advance of solidification is vastly different among different materials. Past research has demonstrated a clear link between the dynamics of a supercooled, glass-forming liquid and its chemical structure and thermodynamic properties referred to as "fragility". In this project, dynamic light scattering, Raman spectroscopy and differential scanning calorimetry are being applied to probe how liquid dynamics are directly affected by simple structural changes created in network-forming systems. The results will form a precise test of a proposed thermodynamic model (Bond Model) presently available. Work will be carried out both by graduate (MS) and undergraduate students providing hands-on research experience to augment their science education. Non-technical AbstractTechnology thrives on exploiting the novel properties of materials. Among these, glassy materials possess unique mechanical, optical and electrical properties of importance for many state-of-the-art devices. However, for their potential to be realized, glassy materials must be solidified from the liquid state without crystallization occurring. This then requires an understanding of the liquid-to-glass transition and in particular an understanding of how chemical structure of the liquid affects the thickening process itself. In this project, visible light scattered by a glass-forming liquid is used to monitor this thickening process on a microscopic level. A series of glass-forming liquids are to be investigated in which the chemical structure can be systematically altered by either increasing or decreasing the average number of chemical bonds present in the liquid. With each modification of the structure, the corresponding changes in dynamical properties of the liquid will be assessed to test predictions of a simple model based upon the average number of bonds present. Graduate (MS) and undergraduate students will conduct this research as means of training the next generation of professional scientists.