Scocchi Giulio, Sergi Danilo, D'Angelo Claudio, Ortona Alberto
University of Applied Sciences, SUPSI, iCIMSI Research Institute, Galleria 2, CH-6928 Manno, Switzerland.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Dec;84(6 Pt 1):061602. doi: 10.1103/PhysRevE.84.061602. Epub 2011 Dec 1.
In molecular dynamics (MD) simulations, interactions between water molecules and graphitic surfaces are often modeled as a simple Lennard-Jones potential between oxygen and carbon atoms. A possible method for tuning this parameter consists of simulating a water nanodroplet on a flat graphitic surface, measuring the equilibrium contact angle, extrapolating it to the limit of a macroscopic droplet, and finally matching this quantity to experimental results. Considering recent evidence demonstrating that the contact angle of water on a graphitic plane is much higher than what was previously reported, we estimate the oxygen-carbon interaction for the recent SPC/Fw water model. Results indicate a value of about 0.2 kJ/mol, much lower than previous estimations. We then perform simulations of cylindrical water filaments on graphitic surfaces, in order to compare and correlate contact angles resulting from these two different systems. Results suggest that a modified Young's equation does not describe the relation between contact angle and drop size in the case of extremely small systems and that contributions different from the one deriving from contact line tension should be taken into account.
在分子动力学（MD）模拟中，水分子与石墨表面之间的相互作用通常被建模为氧原子与碳原子之间简单的 Lennard-Jones 势。调整此参数的一种可能方法是在平坦的石墨表面上模拟一个水纳米液滴，测量平衡接触角，将其外推到宏观液滴的极限，最后将该量与实验结果进行匹配。考虑到最近的证据表明水在石墨平面上的接触角远高于先前报道的值，我们对最近的 SPC/Fw 水模型估计了氧 - 碳相互作用。结果表明其值约为 0.2 kJ/mol，远低于先前的估计值。然后我们在石墨表面上对圆柱形水丝进行模拟，以便比较和关联这两种不同系统产生的接触角。结果表明，在极小系统的情况下，修正的杨氏方程无法描述接触角与液滴尺寸之间的关系，并且应考虑不同于接触线张力产生的贡献。
