New Nonlinear Optical Approaches for Probing the Microscopic Nature of Liquids and Solutions

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When we think of a chemical reaction, we often envision a beaker filled with a solution and sitting on a lab bench. Most chemistry takes place in solution, where the liquid surrounding the reactants and products can affect a chemical reaction in unexpected ways. While chemists have appreciated the complicated nature of solutions for some time, they do not typically consider the container's size to be a factor. This is true of the container is large. However, when the container holding the solution is reduced to just a few hundred nanometers across, or about 1/10,000 the diameter of a human hair, interaction of molecules with the walls of the container alter the solution properties, making the problem even more difficult. With support for the Chemical Structure Dynamics, and Mechanisms A (CSDM-A) Program in the Division of Chemistry, Professor John Fourkas at the University of Maryland-College Park is developing new experimental and simulation methods for characterizing solutions, both in large containers, and under nanoconfinement. Insights gained from the project could advance our fundamental understanding of solutions, as well as enable more accurate measurements, both of which could have broad implications for range of technologies such as chemical separations, lubrication, oil recovery, and catalysis. The project also provides interdisciplinary training of the next generation of scientists, and outreach activities are fostering public appreciation of scientific exploration and discovery. New nonlinear optical spectroscopic approaches are being pursued to address important outstanding problems in liquids and solutions. Working with his students, Professor Fourkas is combining Optical Kerr effect (OKE) spectroscopy with molecular simulations to develop a general approach for measuring the intrinsic density of liquids in nanoconfined environments, which is a crucial property in determining the behavior of a liquid, as well as to study hydrogen bonding interactions between solvents and silica surfaces. The project is also pursuing substantially improved measurements of the high-intensity optical absorption properties of solutions of strongly absorbing molecules and nanomaterials. A new class of methods, 2-beam action (2-BA) spectroscopies, is being developed to make improved measurements of multiphoton absorption cross sections. 2-BA spectroscopies allow for the detailed and accurate characterization of the photophysics of multiphoton fluorophores, and set the stage for the application of analogous techniques to a broad range of other processes that involve nonlinear absorption.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.