Laboratory of Surface and Interfacial Physics (LPSI), University of Mons, 7000 Mons, Belgium.
Laboratory of Surface and Interfacial Physics (LPSI), University of Mons, 7000 Mons, Belgium.
J Colloid Interface Sci. 2019 Mar 22;540:322-329. doi: 10.1016/j.jcis.2019.01.041. Epub 2019 Jan 14.
The thermal fluctuations of the three-phase contact line formed between a liquid and a solid at equilibrium can be used to determine key parameters that control dynamic wetting.
We use large-scale molecular dynamics simulations and Lennard-Jones potentials to model a liquid bridge between two molecularly smooth solid surfaces and study the positional fluctuations of the contact lines so formed as a function of the solid-liquid interaction.
We show that the fluctuations have a Gaussian distribution and may be modelled as an overdamped one-dimensional Langevin oscillator. Our analysis allows us to extract the coefficients of friction per unit length of the contact lines ζ, which arise from the collective interaction of the contact-line's constituent liquid atoms with each other and the solid surface. We then compare these coefficients with those obtained by measuring the dynamic contact angle as a function of contact-line speed in independent simulations and applying the molecular-kinetic theory of dynamic wetting. We find excellent agreement between the two, with the same dependence on solid-liquid interaction and, therefore, the equilibrium contact angle θ. As well as providing further evidence for the underlying validity of the molecular-kinetic model, our results suggest that it should be possible to predict the dynamics of wetting and, in particular, the velocity-dependence of the local, microscopic dynamic contact angle, by experimentally measuring the fluctuations of the contact line of a capillary system at equilibrium. This would circumvent the need to measure the microscopic dynamic contact angle directly.
在平衡状态下，液体和固体之间形成的三相接触线的热涨落可以用于确定控制动态润湿的关键参数。
我们使用大规模分子动力学模拟和 Lennard-Jones 势来模拟两个分子平滑固体表面之间的液体桥，并研究所形成的接触线的位置涨落作为固液相互作用的函数。
我们表明，涨落具有高斯分布，可以建模为过阻尼的一维 Langevin 振荡器。我们的分析允许我们提取接触线单位长度的摩擦系数 ζ，该系数源于接触线组成的液体原子与彼此和固体表面的集体相互作用。然后，我们将这些系数与通过在独立模拟中测量动态接触角作为接触线速度的函数并应用动态润湿的分子动力学理论获得的那些进行比较。我们发现两者之间存在极好的一致性，与固液相互作用以及因此平衡接触角 θ 具有相同的依赖性。除了为分子动力学模型提供进一步的证据外，我们的结果表明，通过实验测量平衡状态下毛细系统接触线的波动，应该有可能预测润湿动力学，特别是局部微观动态接触角的速度依赖性。这将避免直接测量微观动态接触角的需要。
