盐水液滴在砂岩表面润湿性的分子动力学模拟

Molecular dynamics simulation of brine droplet wetting on sandstone surface

关键词:  盐水  砂岩表面  润湿性  分子动力学模拟  吸附能

Key words:  brine  sandstonesurface  wettability  molecular dynamics simulation  adsorption energy

摘要:

采用分子动力学模拟方法研究NaCl对水滴在砂岩表面的微观润湿行为的影响。结果表明:NaCl能降低水对砂岩表面的润湿程度,强亲水的砂岩表面随NaCl质量分数的增大向弱亲水转化;水的润湿角随NaCl质量分数的增加而增大,在NaCl质量分数大于19.6％时则几乎不发生变化;粒子间的结合能垒远大于解离能垒,引起水分子聚集在Na⁺、Cl-周围而增强了盐水液滴的聚集能力,导致润湿角的增大;砂岩表面对水的相互作用能随着NaCl质量分数的增加而减少,但在质量分数大于19.6％时吸附能的变化不大,与润湿角的变化趋势一致。

Abstract:

Molecular dynamics (MD) simulation was performed to investigate the microscopic wetting behavior of water droplets on the sandstone in the presence of NaCl. The simulation results show that NaCl can transform the hydrophilic SiO_2surface into weak hydrophilicity. The wettability of water droplet on SiO_2surface is weakened with brine concentration increasing. The contact angle increases with the increase of the NaCl concentration until the density rises to 19.6％. The potential of mean force (PMF) between water molecules and Na⁺ or Cl- indicates that the binding energy barrier is higher than dissociation energy barrier, which causes water molecules gathering around Na⁺ or Cl-, and therefore leading to the increase of contact angle. The adsorption energy between the sandstone surface and the water molecules decreases with the increase of the NaCl concentration. However, when the concentration is beyond 19.6％, the adsorption energy changes little, which is consistent with the trend of the change in contact angle.