Ultrafast Vibrational Dynamics of Water and Water in Confinement

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

This award by the Solid State Chemistry program in the Division of Materials Research to University of Illinois Urbana-Champaign is to probe fast small-amplitude structural dynamics of water and water in confined spaces using femtosecond infrared and visible laser pulses. All biological systems and many materials contain confined water in tiny pockets of just a few aggregated water molecules. With this award, Professor Dlott will study water trapped inside molecular nanostructures such as reverse micelles and on the surfaces of biological molecules and nanoparticles. An OH stretch excited by a femtosecond pulse is sensitive during its lifetime to spontaneous changes, if the local hydrogen bondings work. When the excitation decays, it is possible to detect molecular groups that receive the energy, and to identify the structure and composition of the confining media. For large-amplitude motions, the PI has developed a unique method using a femtosecond laser-driven shock wave to disrupt the confined water structure. This disruption and spontaneous self-repair can be probed by femtosecond vibrational spectroscopy. A better understanding of confined water will broadly advance the state of knowledge of disciplines from agriculture to zoology, and is needed to understand factors that govern self-assembly of materials and biomolecular dynamics. At present, molecular motions that underlie water's unique properties are not fully understood, especially water in confined spaces. Using a unique femtosecond laser apparatus developed by the PI, fast small-amplitude changes in the hydrogen bonding structure of confined water trapped inside or on the surface of molecular nanostructures can be measured. Sometimes confined water is involved in fast large-scale molecular transformations that completely disrupt its structure. These transformations are difficult to study with conventional techniques. Hence, the PI is developing a method that uses a tiny explosion generated by a femtosecond laser pulse to disrupt the structure of a sheet of confined water of few molecular thick. This disruption and spontaneous self-repair can then be probed by laser spectroscopy. A better understanding of confined water will broadly advance the state of knowledge of different disciplines, and is needed to understand factors that govern self-assembly of materials and biomolecular dynamics. Students and postdoctoral candidates will be trained to be effective problem-solvers, preparing them for future success in a wide range of disciplines. Technologies being developed for high-speed laser spectroscopy will be shared with scientists and engineers at other universities, national laboratories and industries, and would lead to improved products for imaging science and lithography.