Using Excitations to Understand and Predict Dynamic Properties of Amorphous Condensed Matter

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professors Cicerone and McDaniel of The Georgia Institute of Technology will develop a novel framework for rationalizing liquid dynamics by connecting fundamental molecular relaxation events to macroscopic properties. Their approach will combine experimental measurements of relaxation dynamics with simulations to elucidate how molecular excitations facilitate motion across the complex potential energy landscape in glasses and liquids, with intrinsic barriers correlated to thermodynamic quantities of the system. The team will use a combination of neutron scattering, Raman spectroscopy, and molecular dynamics with ab initio and machine-learning potentials to validate their framework and explore the universality of liquid behavior across several different molecular structures, classes of inter- and intramolecular forces, and pressures. Their studies could enable the prediction of macroscopic relaxation and transport processes of liquids based on fundamental thermodynamic parameters, which could lead to new design principles for tailoring bulk properties for various technical applications. The Cicerone and McDaniel groups consistently provide research experience and opportunities for undergraduate students and participate in several educational outreach activities each year, introducing scientific concepts to local K-12 students. Transport and relaxation in liquids and glasses occur through microscopic cooperative rearrangements on picosecond timescales and Angstrom length scales. The Cicerone and McDaniel labs have recently quantified the population of particles involved in these elemental relaxations and have shown that the activation free energy for these collective relaxation processes is proportional to that of crystallization for simple liquids. In this project, they will determine how to find these activation barriers for complex systems without a well-defined melting point. They will also connect molecular structure with the topology of sequential microscopic reorganization events that lead to structural relaxation. Finally, they will focus on systematically adapting ab initio force fields to reproduce THz collective motion observed in experiments. These studies will seek to quantitatively reproduce the temperature and pressure dependence of transport and dynamics measured using quasi-elastic neutron scattering, THz Raman scattering, and simulation. Success in these steps will help realize improved efficiency in designing materials and liquids with targeted properties. 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.