In this project supported by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor Mikhail Anisimov of the University of Maryland College Park and his research group will employ static and dynamic light scattering, microrheology, slow scanning adiabatic calorimetry, optical and electron microscopy, and X-ray and neutron scattering to characterize the structure of aqueous solutions of alcohols and small amphiphilic ions. The general goal of the research would be to provide useful experimental data and insight into the question of equilibrium or long-lived mesoscale structures.
The results of the proposed research may have a broad impact on the understanding of the role which water and aqueous solutions play in nature, industry, and in biological systems. In particular, the research may be relevant to various possible applications, such as nano-encapsulated oxygen delivery or protein unfolding and protein dehydration in aqueous solutions, and new smart materials resulting from self-assembly in solution.
The project addressed a fundamental, yet highly controversial, issue in the physical chemistry of aqueous solutions, namely, the existence of long-lived, with the size of hundreds of nanometers, inhomogeneities in aqueous solutions of small amphiphilic molecules. The existence of such inhomogeneities was reported, discussed, and disputed in the literature for the last forty years; however, a commonly accepted understanding was not achieved. In this project the results, obtained from light-scattering, small-angle neutron scattering, and confocal microscopy experiments and molecular dynamics simulations on binary solutions of tertiary butyl alcohol, isopropyl alcohol, 3 methyl pyridine, and 2-butoxyethanol and on tertiary solutions of tertiary butyl alcohol–water–hydrophobic compounds (cyclohexane and propylene oxide), led to the development of the concept of mesoscale solubilization, a phenomenon intermediate between molecular solubility and macroscopic phase separation. It was concluded that molecular clustering (inherent to the amphiphilic solute-water binary solutions) could stabilize the mesoscale inhomogeneities in ternary systems (water-amphiphilic solute-oil), leading to mesoscale solubilization. Thermodynamics of supercooled water (ordinary and heavy water) and of two popular water-like models were also studied. Based on recent experiments and computer simulations, it was suggested that liquid water at low temperatures is a "mixture" of two alternative molecular configurations with different density and entropy. An explicit equation of state based on this idea was formulated and the best description of the thermodynamic anomalies of supercooled water was achieved. The project stands at the intersection of physical chemistry, molecular physics, materials science, chemical and biomolecular engineering. It contributes to the further development of mesoscopic equilibrium and nonequilibrium thermodynamics, a growing field that can be defined as a semi-phenomenological approach to phenomena where a meso length-scale - intermediate between the atomistic scale and the macroscopic scale - emerges and where such a length explicitly affects the properties and phase behavior. This fundamental research project is in an area of untapped commercial potential. Most industries, from agrochemicals to pharmaceuticals, detergents, all develop products that are colloidal dispersions. Product stability is a major problem in such multi-component mixtures, and industries spend a lot of time and resources to create stable products with long shelf life. Results from the project could help such industries by providing an alternative to traditional stabilization techniques. For example, the introduction of small amphiphilic molecules instead of surfactants could highly benefit the pharmaceuticals industry by aiding the development of products with lower toxicity and easier biodegradability. There is a strong demand from biotechnology and geosciences for reliable prediction of the properties of supercooled water and aqueous solutions. This is particularly important for the development of meteorological and climate models and novel cryoprotectans to preserve bio cells or tissues. At atmospheric pressure, water can exist as a metastable liquid down to 235 K, and supercooled water has been observed in clouds down to this temperature. Furthermore, the thermodynamic properties of cold and supercooled water at high pressure are needed for the design of food processing. The project provides an important database for these applications.
