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April 20th 2019

Researchers from this FOM Industrial Partnership Programme study the growth of bubbles in oversaturated liquids. Carbonated beverages, such as soft drinks, beer or champagne are examples of an oversaturated liquid. At the moment you open a bottle of champagne, for example, the pressure in the bottle drops and the liquid changes from saturated to oversaturated. The dissolved carbon dioxide gas escapes and forms bubbles that move to the surface. If you open the bottle carelessly then so many bubbles form that the champagne bursts out of the bottle.

Bubbles in oil
Oversaturated liquids occur in nature if a saturated liquid moves to a location with a lower pressure, for example magma that escapes during a volcanic eruption or crude oil during the exploitation of an oilfield. Crude oil is often located in porous rock. Whether or not it is feasible to extract the crude oil from the ground partly depends on how bubble growth takes place in rock.

Researchers use a sort of high-tech soda machine to study bubble growth under such conditions. In this machine they produce a saturated carbon dioxide solution at a pressure of ten bars. They subsequently apply the solution to a silicon chip in which miniscule holes have been etched. These holes have been made water-repellent. Consequently as soon as the pressure decreases bubbles will develop from inside these holes. With this setup the physicists can study how bubbles in the vicinity of walls grow and how growing bubbles influence each other.

Growth rate
The researchers compare, for example, the growth rate of a bubble in three situations. Above the chip, the bubble grows quickest due to convection (a spontaneous flow around the bubble). Under the chip, convection is partly hindered so the bubble grows less quickly. By letting the bubble grow between two different chips, the convection can be completely suppressed. In that case the bubble grows the slowest. 

The behaviour of three bubbles in a row strongly depends on the distance between them. If this is small enough then two bubbles will merge, creating enough space for the third bubble to carry on growing. Conversely, bubbles at a larger distance from each other have the tendency to grow at the same speed.