An international research team led by Princeton University has constructed a set of rules to describe the way tiny droplets of liquid spread along flexible fibres. This knowledge will help understand why liquid soaks into some materials, beads atop others and leaves others matted and clumped.

The researchers were surprised to find that the size of a droplet was important in determining whether it would spread into a thin column between two glass fibres, or remain in a bead shape. They concluded that spreading occurs when the distance between the fibres is such that it takes less energy for the liquid to form a column than remain as a drop. They were also able to calculate the optimum drop size for achieving maximum spread of liquid along the fibres.