Role of Gas Pressure and Molecular Weight in Bubble Pinch-Off from an Underwater Nozzle

We report on experiments that explore the role of gas pressure and molecular weight near the pinch-off of an air bubble from an nozzle submerged in water. We use high-speed video to image the dynamics close to the singularity occurring at pinch-off.\footnote{N.~C.\ Keim et al., \emph{PRL} 97, 144503 (2006).} As the neck collapses to a radius of several microns, the effects of the Bernoulli pressure associated with gas flow inside the neck begin to alter the bubble's shape and evolution, as was recently proposed.\footnote{J.~M.\ Gordillo, M.~A.Fontelos, \emph{PRL} 98, 144503 (2007).} We address the role that the gas plays in creating satellite bubbles during the pinch-off process, and its influence on the evolution of perturbations to axisymmetric collapse.\footnote{L.~E.\ Schmidt et al., in preparation.}