Key Laboratory of Low-Grade Energy Utilization Technologies and Systems of Ministry of Education, Chongqing University , Chongqing 400030, China.
Langmuir. 2014 Mar 11;30(9):2394-400. doi: 10.1021/la4044705. Epub 2014 Feb 27.
Molecular dynamics simulations are applied to study the spreading behavior of a nanosized water droplet that contains freely moving Na(+)/Cl(-) ions subject to an imposed electric field parallel to a solid surface. Results show that the positive and negative ions move relatively freely in response to an applied electric field, whereas polar water molecules realign themselves. These localized behaviors of the ions and the polar molecules are affected by both the applied electric field strength and the ion concentration, which in turn determine the deformation and spreading of the droplet on a solid substrate. The presence of the freely moving ions causes the ion-containing droplet to spread differently from a droplet of pure water. In a weak electric field of 0.05 V/Å, a droplet of a lower ion concentration spreads asymmetrically and the spreading asymmetry is considerably smaller than that associated with a pure water droplet of the same size. In a stronger field of 0.1 V/Å, a droplet of a higher ion concentration spreads symmetrically and completely wets the solid surface whereas a less ionically conducting droplet undergoes an asymmetric-to-symmetric transition in spreading until it reaches equilibrium.
运用分子动力学模拟研究了含有自由移动的 Na(+) / Cl(-) 离子的纳米水滴在平行于固体表面的外加电场作用下的铺展行为。结果表明，正、负离子在外加电场作用下相对自由地移动，而极性水分子重新排列。离子和极性分子的这些局域行为受到外加电场强度和离子浓度的影响，进而决定了液滴在固体基底上的变形和铺展。自由移动离子的存在导致含离子液滴的铺展与纯水液滴不同。在 0.05 V/Å 的弱电场中，较低离子浓度的液滴呈不对称铺展，且铺展不对称性明显小于相同尺寸的纯水液滴。在 0.1 V/Å 的较强电场中，较高离子浓度的液滴呈对称铺展并完全润湿固体表面，而离子电导率较低的液滴在铺展过程中经历从不对称到对称的转变，直到达到平衡。
