Capillary Adhesion on Rough Surfaces: Is Splitting Droplets Beneficial?

A wetting droplet confined between two surfaces will pull them together due to capillary forces. This mechanism is believed to (at least partially) explain how many species of insects adhere to surfaces so well — they secrete a thin film of fluid beneath their feet to attach themselves. Close observations of the fluid in certain species have revealed it to be a water-in-oil emulsion. One suggestion for why this is preferred is that the emulsion droplets themselves form liquid bridges, and that splitting into a large number of small bridges strengthens adhesion. However, there has been debate as to whether this is actually the case in reality: does droplet splitting really increase the adhesive force for physiologically relevant wetting properties? We suggest that droplet splitting may be particularly beneficial in ensuring good adhesion to a rough surface, and discuss some fluid mechanical features of drops on rough surfaces that give rise to this improvement.