RUI: Understanding Polyethylene Glycol as a Chemical Solvent in Bulk and Under Confinement

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor Markus Hoffmann of State University of New York – Brockport (SUNY Brockport) is combining experimental and computational studies to advance polyethylene glycol (PEG) as a green chemical solvent. The specific goal of the project is to explore how the interplay of inter- and intramolecular interactions impact the properties of polyethylene glycol (PEG) solutions in bulk and within confined surroundings exemplary of heterogeneous catalysis. PEG has been successfully used in chemical synthesis as a safe and environmentally benign solvent as it is nontoxic and biodegradable. Despite these synthesis successes, very little is known regarding how PEG behaves as a chemical solvent. The intermolecular interactions in PEG by itself are quite complex with multiple possibilities for intra- and intermolecular hydrogen bonding. The complexity increases further when PEG is confined in mesoporous materials typically used for heterogeneous catalysis. Professor Hoffmann will unravel the complexity of studying these interactions by examining molecules that are structurally related to PEG but simpler. The derived insights have the potential to not only impact the development of applications where PEG is used as a chemical solvent but many other areas as well including polymer formulation and additives for health/personal care products. The research is conducted with undergraduate and Master students who are gaining valuable experience in sophisticated experimental and computational research not only at SUNY Brockport but also from collaborating research groups at TU-Darmstadt, Germany. The project utilizes a synergistic experimental and computational approach to meet its objectives. Results from bulk measurements of density, viscosity, and self-diffusion measurements are used to validate the force fields used in molecular dynamics (MD) simulations. Surface tension and dynamic light scattering measurements are conducted to detect and characterize the formation of aggregates of solutes that may form in PEG, especially if the solutes have limited solubility in PEG. The MD simulations provide molecular level insights into the dynamics of the system that are necessary to explain structure property relationships and aggregation propensities. Simulations of systems confined in mesoporous materials are conducted to reveal how the additional interactions with the host surface modify the dynamics and intermolecular interactions of the system compared to bulk behavior. The insights from these simulations will then guide the interpretation of solid-state NMR experiments. The project leverages a longstanding collaboration of Prof. Hoffmann with the research groups of Prof. Buntkowsky and Vogel at TU-Darmstadt, Germany where solid-state NMR dynamic nuclear polarization (DNP) experiments are caried out. 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.