RUI: Complex Dynamics in Glass-forming Oxide Melts

非技术描述：氧化物玻璃在重要的商业应用中占有突出地位，从高速光纤通信到无数智能设备中的防震触摸屏。这些材料的发展得益于其独特的“球和棒”原子结构，其中原子（球）通过共价键（棒）相互连接以产生连续的网络，其中键密度在很大程度上决定了材料对施加剪切力的响应（刚性或柔性）。然而，最近的一些观察结果与这个简单的模型不一致，似乎可以通过在省略某些冗余连接时获得的“最弱连接”的替代网络来更好地解释。该项目旨在通过产生急需的玻璃动力学的新观察结果来更深入地了解原子级玻璃结构最终如何决定材料性能，这些观察结果可以明确地测试模型预测。工作主要由本科生完成，他们获得了宝贵的研究技能，作为他们迈向高级学习的一部分。该项目还通过创建和交付一门新的实践材料科学课程，将周围K-12社区的服务学习活动结合起来，为非理工科学生提供了一窥科学和工程研究的兴奋之处。技术细节：氧化玻璃的性质从软到硬不等，这取决于共价键网络在结构中渗透的机械约束程度。性质还包括熔体粘弹性弛豫的复杂动力学（非阿伦尼乌斯速率和非指数衰减），这在网状形成氧化物中很少研究。最近，两种相互竞争的模型提出了不同的方法，其中热力学可能与静态键约束相结合，以预测玻璃化转变温度和脆性等粘弹性特性。一种假设具有热强度层次的原子约束，而另一种则强调在某些刚性物质上通过粗粒化获得的平均场结构。在这里，动态光散射（以及高分辨率拉曼光谱）在选定的氧化物系统上进行，以提供两个模型的关键测试，同时也提供了这些难熔熔体中弛豫的急需表征。这些研究主要由本科生进行，提供多种形式光谱学的实践经验，并有助于培养下一代科学实践者。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: Oxide glasses feature prominently in important commercial applications ranging from high-speed optical fiber communications to shock-resistant touchscreens found in a myriad of smart devices. Development of these materials is informed by their unique "ball and stick" atomic structure, wherein atoms (balls) are interconnected by covalent bonds (sticks) to produce a continuous network where bond density largely determines the response (rigid or flexible) of the material to applied shear forces. However, several recent observations are inconsistent with this simple model and appear to be better explained by appealing to an alternative network of "weakest linkages" obtained when certain redundant connections are omitted. The project seeks to attain deeper understanding of how atomic-level glass structure ultimately determines material properties by generating much needed new observations of the glassy dynamics that can definitively test model predictions. Work is performed primarily by undergraduate students who gain valuable research skills as part of their trajectory toward advanced studies. The project also offers non-science students a peek at the excitement of science and engineering research through the creation and delivery of a new hands-on materials science course that incorporates service-learning activities in the surrounding K-12 community.TECHNICAL DETAILS: The properties of oxide glasses vary from floppy to rigid depending on the degree to which mechanical constraints imposed by a network of covalent bonds percolate within the structure. Properties also include the complex dynamics (both non-Arrhenius rates and non-exponential decay) of the viscoelastic relaxation of melt which has rarely been studied in network-forming oxides. Recently, two competing models propose differing ways in which thermodynamics might be integrated with static bond constraints to predict viscoelastic properties like the glass transition temperature and fragility. One assumes atomic constraints with an hierarchy of thermal strengths while the other emphasizes a mean field structure obtained by coarse-graining over certain pockets of rigid matter. Here, dynamic light scattering (together with high-resolution Raman spectroscopy) is performed on a selection of oxide systems to provide a critical test of the two models while also providing much needed characterization of the relaxation in these refractory melts. These studies, conducted primarily by undergraduate students, provide hands-on experience with multiple forms of spectroscopy and serve to train the next generation of science practitioners.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.