Structure, Energy And Hydrogen Bond Relaxation Time Of The Ordered Water Monolayer On Pattern Surface

Nanoscale is referred to the size which is ranged between1-100nanometers, which may arise a diverse set of technical and scientific contextsand applications since the1990s. The nanoscale materials usually behave someunique properties, such as surface effect, small size effect and quantum tunnelingeffect, which are different from those of the bulk water or atomic ones. Based on theseunusual properties, many scientists performed researches on the relative basal theoryof nanoscale objects and manufactured some novel products. Interfacial properties ofnanoscale materials are important parts of nanoscience. Nanoscale water on substratesis a very important issue. The study of interfacial water may help us to understand theprocess of surface corrosion and the property of preventing surface adsorption, andmay be applied in manufacturing micro flow devices and self-cleaning materials.Water plays an important role in the evolution of life, that is named as the "the matrixof life", and where there is no water there is no life. These study also help uscomprehend the biological process, such as protein folding and formation ofmembrane.The importance of water relates to its special property, which is based on thespecial structure. The most important feature of water is that the water molecule canform hydrogen bonds among the water molecules or with other molecules. Manyresearches have shown that the water molecules on the surface presented differentproperties than those of the bulk water, and so did those of the individual watermolecule. Water always completely wet water itself due to the hydrogen bonds amongwater molecules. Fang et. al. predicted that the water monolayer may exhibit anordered feature on certain surfaces, which results in the novel phenomenon “orderedwater monolayer does not completely wet water”. Since the year of2010, severaltheoretical and experimental works have found the similar phenomena of “orderedwater monolayer that does not completely wet water” on several real surfaces, such ason talc surface, Pt(100) surface, hydroxylated Al2O3surface, hydroxylated SiO2surface, sapphire c-plane surface, self-assemble monolayer (SAM) surface with the terminal of–COOH. All of these results may show the generality of the roomtemperature “ordered water monolayer that does not completely wet water” in nature.In this thesis, we continue to study the novel phenomenon by molecular dynamicssimulations. we study the influence of the ordered water monolayer on the solidsurface with different charge and unit cell size on the ordered monolayer and thebehavior of hydrogen bonds, including the structure of monolayer, energy andhydrogen bond relaxation time, which help us understand the property of orderedmonolayer. First of all, the appropriate charge pattern contributes to the specialordered monolayer, where the water molecules are mainly two states, that state1withoxygen atoms attracted by the positive charged sites and state2with-OH bondspointing towards the negative charged sites. With the change of charge and bondlength, the water molecules in monolayer present different structure and the property.We calculate two parameters related to two water states in the monolayer, and findthat, with the increase of charge, the water molecules become more ordered. With thebond length increasing, the water monolayer become ordered at first and then theordered structure gradually is destroyed. We calculate the electrostatic interactionbetween the charge on the surface and the water molecules in monolayer. Through thecoupling of the binding charge, the water molecules in the monolayer become orderedand form an ordered two-dimensional hexagonal configuration. These electrostaticinteraction energies highlight the effect of the neighbor charges contributing to theformation of the ordered water monolayer. The density and potential of mean forcereveal the adsorption interaction of the solid surfaces at these valleys. There isadsorption from the charged surface and form the ordered monolayer, which isdifferent from the bulk water. At last, we calculated the number and the relaxationtime of the hydrogen bonds in the monolayer. The water molecules in monolayer canform two hydrogen bonds with water molecules in the same layer. For this specialordered monolayer, the stable water molecules make a2D hexagonal hydrogen bondnetwork. The ordered water structures that reduce the possibilities of hydrogen bondformed between the monolayer and the contacting water molecules above themonolayer. The relaxation time of hydrogen bond in the monolayer is longer than that in bulk water. Studying these properties of ordered monolayer can help us tounderstand the mechanism of the formation of an ordered monolayer, and it can beused to make novel materials in future.