Self-similarity has been the paradigmatic picture for the pinch-off of a
drop. Here we will show through high-speed imaging and boundary integral
simulations that the inverse problem, the pinch-off of an air bubble in water,
is not self-similar in a strict sense: A disk is quickly pulled through a water
surface, leading to a giant, cylindrical void which after collapse creates an
upward and a downward jet. Only in the limiting case of large Froude number the
neck radius h scales as h(−logh)1/4∝τ1/2, the purely
inertial scaling. For any finite Froude number the collapse is slower, and a
second length-scale, the curvature of the void, comes into play. Both
length-scales are found to exhibit power-law scaling in time, but with
different exponents depending on the Froude number, signaling the
non-universality of the bubble pinch-off.Comment: 5 pages, 2 figures. Figure quality was reduced considerably and
converted to greyscale to decrease file siz