CAREER: Standing Out in a Crowd, Neutron Based Methods to Study Molecular

University Of Cincinnati Main Campus, Cincinnati OH

Investigators

Abstract

Neutron scattering is a powerful and elegant experimental technique. Vital in studying hydrogen-rich biological and polymeric materials, magnetism, imaging, and exploring exotic states of matter; neutrons have clear role in the national scientific repertoire. This project will develop novel neutron scattering experiments – leveraging the unique advantages of neutrons to address fundamental questions in molecular transport emerging from crowded aqueous environments. This project will combine these research activities with the creation of a teaching module within the mass transport course for chemical engineers using neutron scattering to demonstrate the molecular origins of diffusion in simple liquids; along with the development of a new undergraduate course focused on "Large Scale Science". The overwhelming majority of neutron science in the US is conducted at large facilities, cementing the notion that some science simply requires shared national facilities. Neutron sources are significant national investments, the "Large Scale Science" class will focus on how neutron scattering facilities and other large scale scientific facilities come to be, what they accomplish, how they operate, and finally, how they fit into the national and international scientific landscape. Students will visit national facilities and representative leaders to learn more about the process and priorities of large-scale science. Molecularly crowded environments are structurally complex and dynamic. Molecular transport via diffusion is often observed to become anomalous within these environments. This means that the mean square displacement (MSD) exhibits a weaker time dependence than the typical Brownian diffusion mechanism. Solutes may become trapped for arbitrarily long residence times, demonstrate highly correlated relaxation times, and/or coupled dynamics to the local solvent. Neutrons offer unique strategies to probe such questions when combined with contrast matching and scattering cross-section manipulation strategies. Selective deuteration is the enabling methodology for neutron scattering experiments in this project. Deuteration will be deployed in several ways to highlight the solute molecule motions in crowded environment as if it were a single particle in dilute solution. This will isolate the single molecule contribution to anomalous diffusion. This can be compared then to the local relaxations of the solvent or other medium, such as a hydrogel, to isolate localized hydrodynamic effects versus collective effects. Structural characterizations of the same systems will inform our theoretical understanding of the ergodicity of the system, the violations of which, can explain some of the anomalous phenomena through better understanding of the flaws in the assumed structural and dynamical distributions at the heart of existing models. 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.