RUI: Complex Dynamics in Glass-forming Oxide Melts

非技术描述：氧化物玻璃在从高速光纤通信到无数智能设备中的防震触摸屏等重要商业应用中具有突出的功能。这些材料的发展是由其独特的“球和棒”原子结构所告知的，其中原子（球）通过共价键（棒）互连以产生连续网络，其中键密度在很大程度上决定了材料对施加的剪切力的响应（刚性或柔性）。然而，最近的几个观察结果与这个简单的模型不一致，似乎可以更好地解释，呼吁一个替代网络的“最弱的联系”时，某些冗余连接被省略。该项目旨在通过产生急需的新的玻璃动力学观测结果来更深入地了解原子级玻璃结构最终是如何决定材料特性的，这些观测结果可以明确地测试模型预测。工作主要由本科生进行，他们获得了宝贵的研究技能，这是他们走向高级研究的一部分。该项目还通过创建和提供新的实践材料科学课程，结合K-12社区的服务学习活动，为非科学专业的学生提供了一个窥视科学和工程研究的兴奋点。氧化物玻璃的性质从松软到刚性变化，这取决于共价键网络施加的机械约束在氧化物玻璃中渗透的程度。结构 性质还包括复杂的动力学（非阿耳修斯速率和非指数衰减）的熔体的粘弹性松弛很少被研究在网络形成的氧化物。最近，两个相互竞争的模型提出了不同的方式，其中热力学可能与静态键约束相结合，以预测粘弹性的玻璃化转变温度和脆性。一个假设原子的约束与层次的热强度，而另一个强调通过粗粒化在某些口袋的刚性物质的平均场结构。在这里，动态光散射（连同高分辨率拉曼光谱）进行氧化物系统的选择，以提供两个模型的关键测试，同时也提供了急需的特性，在这些耐火材料熔体的松弛。这些研究主要由本科生进行，提供了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NSF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.