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Influence of Nanostructure on Hydrophobic Properties at TiO2 Surface Studied by Molecular

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Tutor: ChenMingJun
School: Harbin Institute of Technology
Course: Mechanical Manufacturing and Automation
Keywords: hydrophobicity,nanostructure,rutile,molecular dynamics,contact angle
CLC: O614.411
Type: Master's thesis
Year:  2011
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Abstract:
Wettability is one of the important properties of solid surface, usually characterized by contact angle of liquid on solid surface when three-phase equilibrium. Inspired by the natural hydrophobic material, artificial hydrophobic material are of a wide range of applications and great research value in the area of self-cleaning, anti-current conductivity, corrosion resistance, low resistance transport, driven flows, pollution prevention and so on, while the hydrophobic surface modification of titanium dioxide is of great significance for medical implant materials, so this paper applies molecular dynamics on the hydrophobic property simulation of surface modified rutile (110) crystal surface, as the theoretical basis for experimental studies using ultra-precision machining in the later time.Hydrophobic properties of solid surface are mainly determined by surface chemical composition and microstructure on it. By constructing different surface nanostructure morphology, such as grating array structure and square pillar array structure, this paper focus on geometry dimensions, crystal orientation, surface exposed atoms to analyse the influence of these factors on the hydrophobic properties of established rutile surface hydrophobic properties and to compare the current water molecules aggregation state with the corresponding macro-wetting state.In the simulation process, based on actual rational analysis, using the physical properties which can characterize surface hydrophobicity such as contact angle measured by droplet profile projecting to (001) or (1¡ª10) crystal face, the number of hydrogen bonds droplet formed near the surface of titanium dioxide, the average number of hydrogen bonds per water molecule droplet formed near the surface of titanium dioxide, the coverage diamater of droplet profile projecting to (001) or (1¡ª10) crystal face near the base surface, to analyze the change rules between these factors and surface hydrophobicity.Through the analysis of the simulation results, it is founded that crystal orientation has an important influence on the surface hydrophobic properties with nanostructure on it. When there are tanks along the [001] direction, it will enhance surface hydrophobic properties compared with perfect surface. When there are tanks along the [1¡ª10] direction, it will weaken surface hydrophobic properties compared with perfect surface. Surface hydrophobic properties change with groove width, protrusion width, groove depth monotonously or oscillatingly depending on crystal orientation. Unsaturated coordinated surface atom density is higher, the worse the surface hydrophobicity. For the square pillar array structure, there will be potential changes in wetting state and the superposition of the weakening effect of groove along [1¡ª10] direction and the enhancement effect of groove along [001] direction, its surface hydrophobicity has more dramatic oscillating change.
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