Nakamura Yoshinori, Carlson Andreas, Amberg Gustav, Shiomi Junichiro
Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Sep;88(3):033010. doi: 10.1103/PhysRevE.88.033010. Epub 2013 Sep 18.
Although the capillary spreading of a drop on a dry substrate is well studied, understanding and describing the physical mechanisms that govern the dynamics remain challenging. Here we study the dynamics of spreading of partially wetting nanodroplets by combining molecular dynamics simulations and continuum phase field simulations. The phase field simulations account for all the relevant hydrodynamics, i.e., capillarity, inertia, and viscous stresses. By coordinated continuum and molecular dynamics simulations, the macroscopic model parameters are extracted. For a Lennard-Jones fluid spreading on a planar surface, the liquid slip at the solid substrate is found to be significant, in fact crucial for the motion of the contact line. Evaluation of the different contributions to the energy transfer shows that the liquid slip generates dissipation of the same order as the bulk viscous dissipation or the energy transfer to kinetic energy. We also study the dynamics of spreading on a substrate with a periodic nanostructure. Here it is found that a nanostructure with a length scale commensurate with molecular size completely inhibits the liquid slip. The dynamic spreading is thus about 30% slower on a nanostructured surface compared to one that is atomically smooth.
尽管液滴在干燥基底上的毛细铺展已得到充分研究，但理解和描述控制其动力学的物理机制仍然具有挑战性。在此，我们通过结合分子动力学模拟和连续相场模拟来研究部分润湿纳米液滴的铺展动力学。相场模拟考虑了所有相关的流体动力学，即毛细作用、惯性和粘性应力。通过协调连续介质和分子动力学模拟，提取了宏观模型参数。对于在平面上铺展的 Lennard-Jones 流体，发现固体基底处的液体滑移很显著，实际上对于接触线的运动至关重要。对能量传递的不同贡献的评估表明，液体滑移产生的耗散与体粘性耗散或向动能的能量传递处于同一量级。我们还研究了在具有周期性纳米结构的基底上的铺展动力学。在此发现，长度尺度与分子尺寸相当的纳米结构完全抑制了液体滑移。因此，与原子级光滑的表面相比，在纳米结构表面上的动态铺展速度慢约 30%。
