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摘要: 以Flow-3D为基础, 对不同微织构表面上液滴的铺展过程进行了动力学仿真, 提出了三相接触线的移动机制, 并用接触线铺展标定律、铺展速度和最终铺展半径评价液滴在微织构表面上的铺展特性。试验结果表明: 液滴在微织构表面和光滑表面上分别满足相应的铺展标定律, 微织构增大了固-液接触面积, 液滴铺展过程获得了额外驱动力, 因而, 铺展速度和最终铺展半径都增大; 在正方形凹坑表面, 最终铺展半径由1.05mm增大到1.30mm, 而在正方形凸起表面, 最终铺展半径达到最大值1.62mm; 相比于微凹坑, 微凸起更有利于液滴的铺展, 由于微凸起的存在, 固-液间接触面积迅速增大, 液滴铺展获得了额外的驱动力, 加上微凸起之间形成的微通道, 三相接触线始终保持连续性特征; 反观微凹坑表面, 虽然固-液间的接触面积增大, 但是三相接触线钉扎在微凹坑内, 随着铺展速度逐渐降低, 液滴最终稳定在平衡位置; 液滴在长方形织构表面上的铺展过程具有各向异性, 平行于微织构方向的铺展速度大, 最终铺展半径为1.13mm, 铺展特性较好, 而垂直于微织构方向的铺展速度小, 由于三相接触线的不连续性, 最终铺展半径为0.94mm, 铺展特性较差。Abstract: The dynamics simulation of droplet spreading process on the different micro-textured surfaces was studied on the basis of Flow-3 D, and the moving mechanism of triple contact line was proposed. The spreading scaling laws of contact line, the spreading velocity and the final spreading radius were used to evaluate the spreading features of droplet on the micro-textured surfaces. Test result shows that droplet on the micro-textured and smooth surfaces meets two corresponding spreading scaling laws respectively. The contact area between solid and liquid increases because of the micro-textures. Because the excess driving force is obtained in the spreading process of droplet, both the spreading velocity and the final spreading radius increase. The final spreading radius on the micro-textured surface with square pits increases from 1.05 mm to 1.30 mm, and the maximum radius on the surface with square bulges is 1.62 mm. Micro-bulge is more beneficial to promote droplet spreading compared with micro-pit. Because of the existence of micro-bulges, the contact area between solid and liquid increases rapidly, the excess driving force is obtained in spreading process of droplet, the micro-channels between micro-bulges form, so the triple contact line keeps continuous feature all the time. While on the textured surface with micro-pits, the triple contact line is pinned in the micro-pits despite of the increase of contact area between solid and liquid, and the droplet eventually stays at the equilibrium position with the decrease of spreading velocity. Moreover, droplet spreading process has anisotropy on the surface with rectangle texture. The flow velocity parallelled to the micro-texture direction is higher, and the final spreading radius is 1.13 mm, which shows a good spreading feature. While the flow velocity vertical to the micro-texture direction is smaller, the spreading radius is 0.94 mm because of the discontinuity of triple contact line, so the spreading feature is poorer.
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图 11 对数坐标系下铺展半径与时间曲线
Figure 11. Curves of spreading radius and time in logarithmic coordinate
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