Chain-Like Structure of Water in the Nanoscopic Scale
Understanding the structure of water at the nanoscopic scale is extremely important for the comprehension of the interfacial phenomena of water, such as the condensation and crystallization of water vapor on surfaces. The behavior of water is well known at the macroscopic level, but information is lacking about the behavior of water molecules at the nanoscopic scale. To learn more about the behavior of water molecules at this small scale, we conducted an experiment that examined the structure of water molecules between two silica surfaces. Using a cantilever-based optical interfacial force microscope (COIFM), we measured force as a function of distance as the molecules became confined between the microscope tip and oxidized sample surface. The force-distance curve surprisingly showed that the force changed in an oscillatory pattern with a periodicity of 3-4 water diameters as the tip and sample surfaces approached each other. Each periodic portion in the curve was composed of an upward arc and a downward sigmoidal shape. The arcs suggest that the water molecules behaved not like a bundle of springs, but like a bundle of chains in which molecules rotated freely. When the upward arcs were correlated with the freely jointed chain (FJC) model, their correlation coefficients (R) were found to be higher than 97%, confirming that the water molecules did form chain-like structures. When we analyzed the data from sigmoidal shapes, we found the shapes were correlated to the transition between bundles of water chains with different chain lengths. The discovery of the chain-like behavior of water enhances our understanding of the interfacial phenomena of water at the nanoscopic scale.
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