Figure 2

Source-hole characterization. (a) Stabilization of finger emerging from a single central source-holes is shown here for increasing V and b ₀. Data is plotted between two non-dimensional quantities μ V/σ and b ₀/R ₀ and experiments were performed for two fluids with large difference in their rheological parameter (see Supplementary Fig. 1(a)). Radius R = 20 mm is kept constant for all cases. Inset image shows an intermediate lifting stage where a circular finger (air) penetrating from a single central source-hole displaces the fluid. The image also shows retreating of fluid from the outer interface. (b) Pictorial representation of how the finger destabilization process evolves before it reaches a stable point for different V and b ₀ values. The pattern left on the cell plates, after the lifting process is complete, shows number of finger formations decrease as b ₀ increases (left to right) until no finger destabilization happens thus shaping the fluid into a smooth circular ring (last image of all rows). Lifting velocity V was varied from 2.5 μm/sec to 12.5 μm/sec (step increase of 2.5 μm/sec) and minimum b ₀ value was taken to be equal to \({50}^{\pm 2}\mu m\) (step increase of 25 μm). All images are from the experiments carried out for fluid-1 and the images for fluid-2 are shown in Supplementary Fig. 2.