a drop of water pinching off from a column of fluid
Three images, taken approximately 1/10,000 of a second apart, show a drop pinching off from a column of fluid. This process occurs in water from a kitchen sink, but it is too fast to see. Images courtesy of Peter Taborek

To Peter Taborek, a drippy faucet is a physics experiment.

Taborek uses high-speed video to capture the motion of drops and bubbles coming apart. Knowing the details of this “pinch-off” process is important when designing inkjet printers, because ink must form a single droplet without trailing liquid. It also is useful in biotechnology when fluid is used on microchips, and it has applications in cosmetics, food and structural materials industries.

“When water drips from your kitchen faucet, it spontaneously forms a long filament of fluid that connects to the falling drop,” says Taborek, UC Irvine physics professor. “The connection point shrinks to zero in a characteristic way that we have studied in detail, down to atomic dimensions.”

In a recent study, published in the journal Physical Review Letters, Taborek and colleague Justin Burton analyze the pinch-off process of xenon bubbles in water. Xenon gas is used in lamps and lasers and has been used as a general anesthetic.

The scientists discovered the main difference between drops and bubbles is the density of the liquid inside. The pinch-off process is bubble-like until a certain density is reached, then the pinching becomes drop-like.

“In addition to providing amusement for physicists and mathematicians, the pinch-off process in drops and bubbles is a model system to study how one thing turns into two things,” Taborek says. “This is common in nature, ranging from the Big Bang to cell division.”

The National Science Foundation funded this study.