羟基化及硅烷化二氧化硅表面润湿行为的分子模拟

Molecular simulation of wetting behavior on hydroxylation and silanization SiO_2 surface

采用分子动力学模拟方法研究水团簇在羟基化及不同链长硅烷化二氧化硅表面的微观润湿行为,通过相互作用能、径向分布函数及扩散系数等参量对微观润湿机制进行分析。结果表明:羟基化二氧化硅表面具有极强亲水性,而硅烷化表面疏水性较强,且疏水性随烷基链增加呈增强趋势;羟基化二氧化硅表面与水分子存在强相互作用,使团簇底部水分子优先向表面移动,并带动其余水分子向表面迁移,促进水团簇在表面铺展,表现出强亲水性;硅烷化二氧化硅表面与水之间主要为范德华作用,不足以克服团簇内部相互作用而破坏水滴结构,表现出强疏水性,随着烷基链增长,表面与水分子的相互作用强度逐渐减弱,疏水性增强。

The microscopic wetting behavior of water on silica surface was investigated by molecular dynamics simulation,in which the hydroxylation surface and silanization surfaces with different alkyl chain length were considered. And the wetting mechanism was analyzed using interaction energy,radial distribution function and diffusion coefficient. It is observed that the hydroxylation surface has strong hydrophilicity. However,the silanization surface exhibits hydrophobicity,and the hydrophobicity is enhanced with lengthened alkyl chain. Also the results indicate that the water cluster has strong interaction with hydroxylation silica surface,which makes the water molecules in the bottom of cluster move towards surface preferentially. In this way the pre-absorbed water molecules would promote the adsorption of the rest water molecules. Then,the water cluster spreads completely on hydroxylation silica surface,and exhibits strong hydrophobicity. On the contrary,the interaction between water cluster and silanization SiO2 surface is mainly originated from van der Waals potential,which cannot overcome the hydrogen-bond interaction between water cluster,and presents strong hydrophobicity. With the increase of alkyl chain length,the van der Waals potential between water cluster and silanization surface becomes weak,and the hydrophobicity is improved.