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

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.