RUI: Complex Dynamics in Glass-forming Oxide Melts

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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.