非平整基底上活性剂驱动的液滴铺展稳定性研究

当含有表面活性剂的液滴放置在液膜上时,受表面张力梯度的驱动,液滴会自发向外铺展。在铺展过程中,初始微小扰动会在非线性作用的影响下产生以指进现象为特征的不稳定现象,并与基底几何特征密切相关。基于润滑理论推导的液膜厚度和活性剂浓度演化方程,采用FreeFEM++语言编写数值模拟程序,应用微软MS-MPI运行库进行并行化处理,模拟了非平整基底对含活性剂液滴铺展过程中指进现象的影响,使用功率谱方法分析了不同波数对应的扰动能量增长规律,探究了Marangoni效应、毛细效应与扰动能量间的变化关系,揭露了非平整基底对不稳定性的影响机理。结果表明,非平整基底对手指形貌影响不大,但对手指下游影响明显;不同波数对应的扰动能量存在不同的演化特征,优势波数为20和7;最大扰动能量出现在初始条件设置扰动处,与平整基底相对比,凹槽基底可抑制扰动发展,总扰动能量约为平整基底的80%;波纹基底可促进扰动发展,总扰动能量约为平整基底的105%,且波纹基底在初期对特定波数的扰动有明显的促进作用。总体地,非平整基底通过改变活性剂浓度分布影响扰动能量,进而影响指进现象。

Liquid spreading behavior and surface wettability of copper ore under controlled sulfuric acid solution and surfactants

To reveal the potential effect of surfactant on improving surface wettability of copper ore,the droplet spreading behavior of sulfuric acid solution contained surfactant was visualized using high-speed camera and an image processing method,and the solid-liquid interaction was discussed in this study.The results show that liquid surface tension and ore surface roughness are the main factors affecting surface wettability.The effect of sulfuric acid solution concentration and surfactants on the surface wettability of ore is revealed via quantitative spreading area,spreading coefficient,and contact angle.The results of droplet spreading experiment show that the higher concentration of surfactant and sulfuric acid solution result in improving the wettability of ore,spreading coefficient,and decreasing contact angle.The“leaching reaction coefficient”and“surface activity coefficient”are introduced to modify the mathematical expression of the equilibrium contact angle.