In this project supported by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor Vladislav Sadtchenko of the George Washington University and his graduate and undergraduate students are investigating the structure and dynamics of deeply supercooled water and aqueous solutions using calorimetric, optical and mass spectroscopic techniques. The novel experimental approach relies on rapid heating of pure and doped amorphous solid water films vapor-deposited on a substrate at cryogenic temperatures. The rapid heating employed in such experiments makes it possible to avoid significant crystallization of the aqueous films and thus to study water in so-called "No Man's Land" temperature range, i.e., where data on water's properties is lacking. The principle goals of the research are: 1) to facilitate development of a comprehensive fundamental description of thermodynamics and molecular kinetics of water by providing experimental data on it s properties in a previously inaccessible temperature range, 2) to gain insights into the molecular kinetics and structure of water in the presence of various hydrated chemical species, and 3) to reconcile often conflicting results of the past experimental studies of supercooled water.
Due to the ubiquitous presence of water in nature and its role in a multitude of environmental, biological, and industrial processes, the result of these studies will have an impact on a great variety of applied fields of science. The research activities are also important for advancement of the scientific method. Potential application of the fast scanning calorimetry technique in research on other (non-aqueous) systems are numerous and may include studies of the relaxation phenomena in polymers and other commercially significant materials. The proposed research activities will contribute to personnel development in the US by providing research training of a graduate (Ph.D.) and several undergraduate students. The broader impact of the work will also be achieved through a public outreach program in the greater Washington DC area.
Water plays central role in myriad of biological and environmental processes. Under a variety of conditions, the most important and interesting phenomena occur not in bulk of water samples, but at liquid-vapor and liquid-solid interfaces. Furthermore, in many important physical, chemical, biochemical, and environmental processes, water is present in the form of sub-nanometer clusters, nanoscale solid or liquid particles, and ultrathin films, i.e., under condition of extreme confinement. Examples of such processes include protein and nucleic acid hydration, environmentally important chemical reaction in quasi-liquid layers in surfaces of stratospheric polar clouds; and interstellar and interplanetary chemistry where water may be present in highly microporous amorphous form. Due to its role in broad range of natural phenomena, confined water has been the focus of intense experimental and theoretical scrutiny for decades. In addition to applied interest in understanding properties of water under confinement is important for developing a comprehensive fundamental picture of relationships between various condensed phases of H2O. Microscopic H2O aggregates are uniquely amendable to modern computational studies. In fact, ASW nanoparticles and smaller clusters are often considered as an idealized simplified systems for theoretical investigations which results can potentially be used to understand properties of bulk-like hydrogen bonded systems. Using fast scanning calorimetry technique, Dr. Sadtchenko and his students have conducted extensive investigations of pure and doped bulk-like solid water samples, ultrathin solid water films, and microscopic water droplets at the George Washington University. In these experiments, the solid non-crystalline water samples were prepared by condensation on water vapor on a cold substrate (thin metal filament), and subjected to extremely rapid heating. Despite conceptual simplicity of the interrogation method, the data on such properties of the aqueous samples as heat capacity, made it possible to gain numerous insights into possible water behavior under less exotic conditions relevant to biochemical and environmental sciences.
