In this project, supported by the Experimental Physical Chemistry Program, Professor Abraham Stroock of Cornell University and his research group will address two outstanding questions related to supercooled water and water at negative pressures: 1) What are the mechanisms of cavitation of water at negative pressures, and 2) What are the origins of observed thermodynamic and dynamic anomalies in supercooled water? Supercooled water exhibits a number of thermodynamic anomalies that have been extensively studied for the last decades: the temperature dependence of many parameters (e.g., compressibility, expansion coefficient, and transport coefficients) suggests a power-law divergence, at a temperature around -45°C at atmospheric pressure. A number of competing theories of this phenomenon have emerged, but the lack of experimental data has left the question unresolved. This project will entail the first measurements in the supercooled regime of viscosity away from ambient pressure (both positive and negative) and of diffusivity under tension. The tools utilized by the Stroock laboratory include Metastable Vapor Liquid Equilibrium (MVLE), Raman scattering, nuclear magnetic resonance (NMR), and microfluidic device technology. Professor Stroock's work will be complemented by Brillouin scattering, acoustically generated tension and optics-based density studies performed in the laboratory of Professor Frederic Caupin of the Laboratoire de Physique de l'Ecole Normale Superieure. The NSF proposal leading to this award was submitted in response to solicitation NSF 08-602: International Collaboration in Chemistry between US Investigators and their Counterparts Abroad (ICC).
Water is among the most important and most studied substances on earth, yet, the origins of its anomalous thermodynamic, dynamic, and structural properties have eluded complete understanding. Scientific studies and technical developments related to the metastable states of liquid water could have broad impact on research and technology in a number of fields, from plant physiology to molecular modeling to manufacturing. The research conducted in this project may provide not only a fundamental foundation for new applications, but also the experimental tools that can facilitate the broader scientific and technical impacts of that knowledge. The richness of technical components (microfabrication, spectroscopy, environmental controls) and fundamental components (thermodynamics, dynamics, molecular structure) inherent in this project will provide an unusually broad training for students and post-docs involved in this research. Furthermore, the exchange of junior members of the US and French teams will allow these students to engage in the full breadth of the research and gain valuable exposure to a foreign scientific and national culture. Both PIs have a strong track record of involving undergraduates in research projects in their labs, and will actively recruit students to participate in this program. Stroock and his junior team member will also engage in K-12 educational activities such as giving lectures (e.g., How trees drink: the Nature of metastable liquids) at local science museums, home-school events, and teaching programs run by the Cornell NSF-MRSEC.
Intellectual merit: Water is among the most important and heavily studied substances on earth, yet, the origins of its anomalous thermodynamic, dynamic, and structural properties have eluded complete understanding. These anomalies include divergent heat capacity, viscosity, and fluctuations of local structure upon cooling the liquid. Theoretical work over the past several decades suggests that new insights may be gained through the study of liquid water in its metastable states of superheat at negative pressure (in which the liquid wants to boil) and supercooling (in which the liquid wants to freeze). In this project, we have opened new routes into the study of water in these two regimes. Firstly, we have developed strategies of micro- and nano-fabrication that allow us to bring the liquid state deep into both of these regimes either independently or simultaneously (that is, when the liquid wants both to boil and freeze). We have further integrated microelectromechanical sensors into these systems such that we can measure properties along trajectories in pressure, temperature, and density that have not been previously accessible. With this instrument, a microtensiometer, we are poised to make an unprecedented map of the thermodynamics of the liquid state, in particular in the physical regions that have been implicated by theory to control many of water’s odd properties. This device is also compatible measurements of dynamic properties such as viscosity and diffusivity, none of which have been measured under these physical conditions. We are currently pursuing these measurements in our laboratory and with collaborators. In pursuing these developments, we made an unexpected discovery about the process of freezing onto surfaces from supercooled vapors (at temperatures far below the freezing temperature of water). In particular, we found that, on many surfaces, the first moment of condensation of vapor occurs at pressures and temperatures that corresponds to what is expected for the vapor-liquid transition rather than the vapor-solid transition. Importantly, this effect persists at temperatures below -40 Celsius for which it is well-established that any macroscopic volume of liquid freezes nearly instantaneously. This discovery has two important implications: firstly, it allows us to access thermodynamic information about the liquid state in a range of temperatures that has previously been inaccessible to experiments and for which theory predicts unusual phenomena that are closely related to water’s anomalies. Secondly, these measurements provide information on the kinetics of freezing in a scenario that is highly relevant to the formation of ice in the upper atmosphere. We are pursuing these experiments with collaborators in both physical chemistry and atmospheric science. Broader impact: During the funding period of this grant, we became aware that the tensiometer that we were developing for fundamental studies of water could be a valuable instrument for the sensing of water status in plants, soils, and synthetic materials. In particular, this microdevice provides a route to measuring the state of water directly within living plants. This information could provide an unprecedented basis for the management of irrigation of crops with the aim of optimizing water use with respect to yield, quality, and sustainability. We have patented the device and are actively pursuing its application to agriculture and environmental science. Based on our discovery regarding freezing from supercooled vapors, we have initiated a collaboration with climate scientists for whom modeling the process of ice cloud formation represents a major, outstanding challenge. In this collaboration, we are providing new data to inform their models and they are testing the effects of this new information on the long term, global predictions of their climate model. The research in this project has provided a rich, multi-disciplinary context for the training of students at the undergraduate and graduate levels. Two undergraduates working on the project have gone on to PhD programs in STEM fields and one post-doctoral fellow has taken a job with a technology firm. The project has also provided a pedagogically rich context in which to interact with the public and K-12 audiences on scientific contexts. In particular, team members have participated two years in welcoming high school girls from rural communities in Central New York to Cornell campus for a day of hands-on experiments and to learn about opportunities in STEM fields.
