|Ph.D Student||Schlesinger Itai|
|Subject||Water Structure Near Surfaces Studied by High Resolution|
Atomic Force Microscopy
|Department||Department of Physics||Supervisor||Professor Uri Sivan|
|Full Thesis text|
The structure of liquid water near various surfaces is relevant to diverse natural phenomena as well as technological processes including the formation of lipid bilayers, protein folding, cell wall secretion, inner and outer cell organization, ionic channels, enzymatic activity, colloids, paints, separation technologies, anti-freeze coatings, and more. Probing the interfacial water structure is an experimentally demanding task. The tools for this task are required to have high spatial resolution both parallel to the surface and perpendicular to it, since the water structure usually spans a few water molecules away from the surface until reaching the bulk values. The most common techniques used today are x-ray reflectivity, neutron diffraction, ellipsometry, and nonlinear, surface-sensitive spectroscopic techniques. Although having good perpendicular spatial resolution, they all share the common trait of observing the scattered beam in the far field, leading to diffraction limited observations parallel to the surface. In this thesis I describe the design of a new atomic force microscope capable of working in liquid and to resolve features down to the atomic scale in all three axes. This instrument provided us with new information on the interfacial water structure near surfaces with unprecedented resolution. Using this new instrument, we set-out to study two phenomena. First, we found that a large set of electrically neutral solutes called osmolytes tend to regulate the surface charge of silica. The mechanism behind this charge regulation is relevant to biological questions such as protein folding. Second, we proved that the hydrophobic interaction involves a capillary-drying type of phase transition between two approaching hydrophobic surfaces in water. By probing an isolated hydrophobic surface, we show that this phase transition originates from a thin (~5 nm) gas layer which tends to adsorb onto the hydrophobic surface from initially dissolved gases in the water.