二维微柱阵列壁面对活性剂液滴铺展的影响

EFFECT OF TWO-DIMENSIONAL MICROPILLAR ARRAYED TOPOGRAPHY ON SPREADING OF INSOLUBLE SURFACTANT-LADEN DROPLET

针对二维微柱阵列壁面上含不溶性活性剂液滴的铺展过程,采用润滑理论建立了液膜厚度和浓度演化模型,采用数值计算方法得到了液滴的铺展特征及相关参数的影响.研究表明:活性剂液滴在微柱阵列壁面上铺展时,在壁面凸起处衍生出隆起结构,壁面凹槽处衍生出凹陷结构,随时间持续,隆起和凹陷均向两侧移动,且数量不断增加.活性剂液膜流经凸起时,隆起高度呈驼峰形变化.增大预置液膜厚度或活性剂初始浓度,铺展区域隆起和凹陷数量增多,液滴铺展速度加快.增加凹槽深度或减小斜度会使毛细力作用增强,液膜破断可能性加大;增大凹槽宽度可加速活性剂液滴的铺展,加剧液膜表面波动幅度.

For the spreading of liquid droplet containing insoluble surfactant over two-dimensional micropillar-arrayed surface, the lubrication theory was adopted to derive the evolution equations of liquid film thickness and interfacial surfactant concentration, and then the droplet spreading characteristics and the effects of related parameters were numerically simulated. Results show that when the surfactant-laden droplet was spreading over micropillar-arrayed surface, the depression appears at the groove while the ridge is shaped at the bump, and the ridge and the depression move towards both sides gradually, and the numbers of ridge and depression increase. Furthermore, when the surfactant film is flowing over the bump, the height of the ridge presents a hump shape. The numbers of ridges and depressions in the spreading region increase and the droplet spreading velocity accelerates with the improved preset film thickness and initial surfactant concentration. Increasing the groove depth or decreasing the steepness can enhance the capillary force effects, resulting in suffering the rupture possibility of the film. Improving the groove width enlarges the film deformation and promotes the film flow.