Experimental and computational study of triple line shape and evolution on heterogeneous surfaces

Abstract

Wetting of smooth, chemically heterogeneous surfaces was studied experimentally and computationally during the advancing and receding processes. The motion of the triple line is known to play an important role in determining the macroscopic contact angle due to its ability to be pinned at various defect locations on real surfaces. This effect is known to cause contact angle hysteresis. The shape of the triple line during these pinning/de-pinning events on various chemically heterogeneous surfaces was captured using an experimental and a computational technique. The experimental study employed a Modified Wilhelmy Plate Technique. The novelty in the current experimental setup lies in its ability to capture the microscopic triple line shape and its evolution in addition to measuring the local contact angles, which were both studied. The triple line shape was observed to be very sensitive to minor imperfections of the substrate. In addition, Surface Evolver was used to study the triple line shape computationally. Evolver was used to solve the complete three-dimensional problem by minimization of the total energy taking into consideration, both gravity and contact angle hysteresis. The studies showed that the temporal evolution of the triple line was significantly different during the advancing and receding processes based on the nature of the chemical heterogeneity. The results from the current work could be used in the design and fabrication of chemically heterogeneous surfaces for desired wetting applications.