方解石表面结构影响水分子吸附的微观机理

Microscopic mechanism of the influence of calcite surface structure on water molecules adsorption

为研究方解石表面结构对水分子吸附的影响规律和机理,首先利用分子动力学模拟研究水分子在不同类型、不同尺寸的表面结构处的吸附特征,分析其对水分子吸附的影响规律.而后利用分子动力学模拟研究水分子在发育表面缺陷的纳米狭缝中的吸附规律,解释纳米狭缝中的水锁现象.最终,结合悬键特征和表面能理论定量解释水分子在不同表面结构处差异性吸附的机理.研究结果表明:表面结构对于水分子吸附具有重要影响,水分子优先在表面结构处聚集吸附,吸附强度与密度远高于理想表面处;表面结构的尺寸对水分子吸附有较大影响,尺寸越大对水分子吸附越强;纳米狭缝中水分子在表面凸起和空位处快速聚集,形成的吸附凸起结合为水膜阻断流动空间,水锁作用明显;空位表面、凸起表面和理想表面对应的悬键密度和表面能依次为7.275 nm^-2和0.734 J/m 2、6.716 m^-2和0.721 J/m 2、5.098 nm^-2和0.581 J/m 2.空位表面和凸起表面具有更多的反应活性位点、更强的反应活性,因此,水分子优先吸附于空位表面和凸起表面.

To study the influence mechanism of calcite surface structure on water adsorption,molecular dynamic simulation was firstly employed to investigate the adsorption characteristics of water on various calcite surface structure with different types and scales.Then,the water adsorption characteristics in nano-slit with surface defects were investigated,which was used to decipher the formation mechanism of water blocking.Finally,the dangling bond characteristics and surface energy results were combined to explain the differential adsorption mechanisms.Results showed that calcite surface structure had great influence on water adsorption.Water was preferentially adsorbed and aggregated around the surface structure,and the adsorption strength and density were much higher than those on the ideal calcite surface.Size of surface structure also presented a great influence on water adsorption.The larger the structure,the stronger the water adsorption.Water in the nano-slits rapidly aggregated around the surface structure and formed obvious adsorption protrusions.Then the adsorption protrusions combined into a water film and blocked the flow space.The water blocking effect appeared.The dangling bond density and surface energy of the vacant surface,protrude surface,and ideal surface were 7.275 nm^-2 and 0.734 J/m 2,6.716 m^-2 and 0.721 J/m 2,5.098 nm^-2 and 0.581 J/m 2,respectively.There were more active sites with stronger reactivity on the vacant and protrude surface.Therefore,water was preferentially adsorbed on them.