English: By adding a small amount of polymer (such as food thickeners) into water, we prepared a liquid solution that is a bit more sticky and stretchy than water; something that is very similar to saliva or egg white. We then pumped the liquid throughout two opposing nozzles into two circular liquid jets and let them collide into each other. To the naked eye these two jets form a blurred liquid fan. Inspired by the images of flying bullets from Doc Edgerton (MIT pioneer of high- speed imaging), we visualized these phenomena using a high-speed air- gap flash that releases a 20,000 volts arch into the air in less than 300 nanoseconds and captured some mesmerizing patterns that resemble a Christmas tree. The momentum of the impacting jets flattens them into an expanding planar sheet that becomes unstable due to the capillary effect. For these viscoelastic liquids, the stretchiness of the polymers delays the breakup of droplets and leads to the formation of spherical beads and elongated filaments. Each droplet/filament acts as a spherical/cylindrical lens. Using the lens effect we can see a projected image of the background. The hourglass background for the viscoelastic case is positioned in such a way that “the sands of time are stretched in the filaments and then relax in the droplets”. An indirect hint to the fact that polymer chains stretch in the filaments and relax in the droplets.
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