Foams collapse in two different ways—this new insight can purportedly help formulators to better control the prevention or acceleration of foam rupture in formulations.
Recent research in Scientific Reports identified these mechanisms in order to pin down the cause of collective bubble collapse (CBC).
Methods
Tokyo Metropolitan University researchers created a quasi two-dimensional foam out of water, glycerol and a common surfactant; this solution was then squashed between two pieces of glass.
One bubble on the edge of the foam raft was then controllably broken, leading to CBC—these proceedings were captured via in situ observation and a high-speed camera.
Results
Researchers identified two distinct mechanisms by which one broken bubble at the edge led to a cascade of breakage:
- Propagating mode, in which the film of the broken bubble is absorbed into the surrounding liquid film; and
- Penetrating mode, when droplets released from the rupture event break other bubbles as they fly away.
Further testing found that bubbles reacted differently at a microscopic level when the amounts of water in the film varied; for example, a film with a higher amount of liquid released slower droplets. However, the changes in fluid viscosity ultimately did not greatly affect the number of bubbles broken.
Since many current methods to stabilize foam include changing the viscosity, these findings may lead to future strategies that focus instead on combining surfactants to create a more-resistant film.
For the full study and additional figures, visit Scientific Reports.
