液滴在化学非均匀表面上铺展的格子Boltzmann方法模拟

Lattice Boltzmann simulations of droplet spreading on chemically heterogeneous surface

中文关键词: 格子Boltzmann方法  非均匀表面  铺展规律

英文关键词: Lattice Boltzmann method  heterogeneous surfaces  spreading law

中文摘要:

      采用格子Boltzmann方法模拟二维液滴在非均匀表面上的铺展。非均匀表面由两块面积相等但润湿性不同的均匀表面拼接而成，左半部分为亲水表面（θeq=35?），右半部分为疏水表面（θeq=115?）。液滴初始为圆形，位于亲疏水表面交界处。由于表面两侧平衡接触角θeq相差较大，铺展的Young驱动力FY=γlg(cos θeq–cos θD)有显著差异，因而液滴左右呈现出不同的铺展规律。模拟结果显示，铺展可分为三个阶段：第一阶段，液滴向两侧铺展直至疏水侧铺展速度为0，但亲水侧铺展速度始终快于疏水侧；第二阶段，整个液滴向亲水侧运动，直到液滴右侧到达亲疏水表面交界处；第三阶段，液滴在亲水表面铺展直至平衡。当液滴初始位于亲水侧或疏水侧，且其质心与亲疏水表面交界处的横向距离小于50格子时，液滴呈现出三种不同铺展形式，然而由于亲水侧更大的Young驱动力，最终的平衡液滴均位于亲水侧。

英文摘要:

      The lattice Boltzmann method is adopted to simulate the two-dimension droplet spreading on a heterogeneous surface. The heterogeneous surface is made of two surfaces with equal area but different wettability. The left part is the hydrophilic surface (θeq=35?) and the right part is the hydrophobic surface (θeq=115?). Initially, a circular droplet is located on the boundary of the hydrophilic and hydrophobic surfaces. The wettability of the two surfaces is quite different, leading to significant difference of the Young’s driven force on the two sides of the droplet according to the equation FY=γlg(cos θeq–cos θD). As a result, the droplet exhibits distinct spreading law on its two sides. The results show that the spreading process can be divided into three stages. In the first stage，both sides of the droplet move forward until the droplet spreading velocity on the hydrophobic surface reaches zero. The spreading velocity on the hydrophilic surface is always larger than that on the hydrophobic surface. In the second stage, the whole droplet moves towards to the hydrophilic surface, and finally the contact line on the hydrophobic surface reaches the boundary of the hydrophilic and hydrophobic surfaces. In the third stage, the whole droplet spreads on the hydrophilic surface. The results also show that the three different spreading laws are always observed if the horizontal distance between the centroid of the initial droplet and the boundary of the hydrophilic and hydrophobic surfaces is less than 50 lattices; however, the equilibrium droplet always stays on the hydrophilic surface due to stronger Young’s driven force.