Bahadur Ranjit, Russell Lynn M, Alavi Saman
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0221, USA.
J Phys Chem B. 2007 Oct 18;111(41):11989-96. doi: 10.1021/jp075356c. Epub 2007 Sep 26.
Surface tensions for liquid-vapor (lv), solid-liquid (sl), and solid-vapor (sv) interfaces are calculated from molecular dynamics simulations of the NaCl-water-air system. Three distinct calculation techniques based on thermodynamic properties are used to describe the multicomponent mixtures. Simulations of each bulk phase (including a liquid saturated solution) and various interfaces are carried out at both NPT and NVT conditions. The thermodynamic relation for energy difference between interface and bulk phases provides an upper bound to the surface tension, while the energy-integral and test area methods provide direct estimates. At 1 atm and 300 K, the best predictions for surface tensions are sigmasv (NaCl-air) of 114 mN m(-1), sigmasl (NaCl- soln) of 63 mN m(-1), sigmalv (soln-air) of 82 mN m(-1), and sigmalv (water-air) of 66 mN m(-1). The calculated surface tensions from simulations have uncertainties between 5 and 10%, which are higher than measurements for the liquid interfaces and lower than the measurement uncertainty for the solid interfaces. The calculated upper bounds for surface tensions of liquid interfaces compare well with experimental results but provide no improvement over existing measurements. However, the bounding values for solid interfaces lower uncertainty by as much as a factor of 10 as compared to the indirect experimental measurements currently available. The energy-integral and test area methods appear to underestimate the surface tension of water by 10%, which is consistent with previous studies using similar model potentials. The calculated upper bounds of surface tension show a weakly positive correlation with pressure in the 0.1-100 atm range for liquid-solid, liquid-vapor, and solid-vapor interfaces.
通过对NaCl - 水 - 空气系统进行分子动力学模拟，计算了液 - 气（lv）、固 - 液（sl）和固 - 气（sv）界面的表面张力。使用了基于热力学性质的三种不同计算技术来描述多组分混合物。在NPT和NVT条件下对每个体相（包括液体饱和溶液）和各种界面进行了模拟。界面相与体相之间能量差的热力学关系为表面张力提供了一个上限，而能量积分法和测试面积法提供了直接估计值。在1个大气压和300 K时，表面张力的最佳预测值为：sv（NaCl - 空气）为114 mN m⁻¹，sl（NaCl - 溶液）为63 mN m⁻¹，lv（溶液 - 空气）为82 mN m⁻¹，lv（水 - 空气）为66 mN m⁻¹。模拟计算得到的表面张力不确定度在5%至10%之间，该不确定度高于液体界面的测量值，但低于固体界面的测量不确定度。计算得到的液体界面表面张力上限与实验结果比较吻合，但相较于现有测量值并无改进。然而，与目前可用的间接实验测量相比，固体界面的边界值将不确定度降低了多达10倍。能量积分法和测试面积法似乎将水的表面张力低估了10%，这与之前使用类似模型势的研究结果一致。对于液 - 固、液 - 气和固 - 气界面，计算得到的表面张力上限在0.1 - 100个大气压范围内与压力呈弱正相关。
