Surface/interface order in liquids with electrostatic correlations: X-ray scattering studies

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****Technical Abstract****Water, and aqueous solutions containing dissolved ions, are ubiquitous in nature, and electrostatic interactions between aqueous solutions and surfaces drive numerous crucial phenomena in biology, chemistry, geology and environmental science, food technology, etc. Dissolved ions are thought to behave in a number of remarkable ways near interfaces. For example, it is predicted that a charged surface in contact with a solution may attract so many dissolved multivalent ions that they will pack into a ordered interfacial layer, thus not just neutralizing the surface charge but adding an excess of the opposite charge ("charge inversion"). Again, hydrophobic surfaces are counterintuitively predicted to attract dissolved negative ions when in contact with ionic solutions. These and other novel phenomena will be studied using synchrotron X-ray scattering to see directly how the ions are arranged and under what conditions. The knowledge gained from the proposed studies will ultimately help design systems with specific surface/interface behaviors for practical applications. This project will train graduate students in an interdisciplinary environment and give them experience in the use of synchrotron facilities. Liquids-related topics will be incorporated into undergraduate and graduate courses and web-disseminated teaching materials.****Non-Technical Abstract****Water often contains dissolved ions, and the interaction of ionic solutions with other materials is responsible for many crucial phenomena in biology, chemistry, geology and environmental science, food technology, etc. Dissolved ions are thought to behave in remarkable and unexpected ways near solid surfaces. For example, it is predicted that when a charged solid surface becomes wet, the dissolved ions it attracts may form an ordered layer somewhat like a crystal, thus packing in so many ions that the interface actually ends up with a net opposite charge. Again, surfaces that repel water are theoretically predicted to attract negative ions when they touch ionic solutions, which is completely counterintuitive. These and other novel phenomena will be studied by using synchrotron X-rays to look directly at how dissolved ions are arranged and under what conditions. What is learned from the proposed studies may ultimately help design systems with specific properties for practical applications. This project will train graduate students in an interdisciplinary environment and give them experience in the use of synchrotron facilities. Liquids-related topics will be incorporated into undergraduate and graduate courses and web-disseminated teaching materials.