CDS&E: Molecular Dynamics Studies of the Structure, Dynamics, and Formation of Stable Glasses

Colorado State University, Fort Collins CO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports computational and theoretical research to advance understanding of how the properties of glasses and glassy materials depend on how they are made. Amorphous, glassy solid materials have become a part of everyday life. They are used as protective coatings for cell phones and in the drug formulation process. Through a process known as vapor deposition, glass forming materials can be made onto a properly prepared substrate. This process emerged as a method to create glasses with desirable properties, such as increased density, increased mechanical stability, and higher resistance to chemical reactions, as compared to glasses that are prepared by cooling from a liquid. Experiments suggest that the increased ability of molecules to move around on the surface enables them to find more favorable positions for the vapor deposited glass than for ordinary glasses, and that incoming molecules help trap the surface molecules into these favorable positions. Furthermore, the structures obtained by the vapor deposition process exhibit different vibrational properties than the glasses created by other means. The PIs and their team will use the ability of molecular dynamics simulations to track the positions of individual atoms to study the vapor deposition process and to examine the microscopic structures that give rise to the different vibrational properties of the vapor deposited glasses compared to glasses created by cooling at a constant rate. At the completion of the project, it is expected that the insights obtained from the computer simulations will help guide researchers trying to make vapor deposited glasses with desirable characteristics and will elucidate what aspects of a glass's microscopic structure lead to these desirable characteristics. TECHNICAL SUMMARY This award supports computational and theoretical research to study the formation and properties of vapor deposited glasses. Vapor deposition of glass forming materials onto a substrate held at a temperature of around 85 percent of the glass transition temperature produces glasses that have higher densities, lower heat capacities, and higher kinetic, and mechanical stability than glasses formed by the conventional method of cooling from a liquid. Experiments suggest that increased mobility of the molecules at the surface allows the molecules to find lower energy configurations, and that incoming material traps the molecules into these lower energy configurations. The PIs and their team will use molecular dynamics simulations to study the vapor deposition process and the structural properties of glasses formed through vapor deposition, and compare glasses formed this way to those formed by cooling at a constant rate. Since molecular dynamics simulation are able to track individual atoms, the group will examine the dependence of the dynamics of the vapor deposited glasses on the substrate temperature and on the distance from the substrate and the free surface. Furthermore, the research will examine differences in the microscopic structure and the vibrational density of states of glasses with different kinetic and mechanical stability that are created by vapor deposition at different deposition rates, and by cooling at different cooling rates. This study will help researchers understand what influences the kinetic and mechanical stability of glasses, and aid researchers in making vapor deposited glasses with desired characteristics.