Scientists Finally Solve the Mystery Behind Foam Drainage
Scientists have finally solved a long-standing puzzle about how liquid drains from foams. A team from Tokyo Metropolitan University discovered that drainage depends on bubble movement, not traditional surface-tension models. As a result, their findings reshape how we understand soft materials.Foams appear simple, yet their behavior is surprisingly complex. For example, liquid often drips from foam sprayed on a surface, even when the layer is not very tall. Earlier theories could not explain why this happens so easily.
Why Old Models Fell Short
Classic models suggest that foams must reach nearly one meter in height before drainage starts. These estimates rely on osmotic pressure, which depends on bubble size and surface tension. However, real foams drain at heights of only a few tens of centimeters, creating a clear mismatch.Foams play a role in everyday items, from cleaning products to medical formulations. Therefore, understanding their behavior is crucial for designing materials that hold or release liquid in predictable ways.
Watching Bubbles in Motion
Professor Rei Kurita and the research team created a wide range of foams using different surfactants. They placed the foams between transparent plates to observe how they changed during drainage. This setup helped them see what truly happens inside.Their results revealed a universal pattern. The height at which drainage starts is inversely linked to the foam’s liquid content. This held true regardless of bubble size or surfactant type. More importantly, the team found that bubbles begin to shift and realign when drainage starts.
A New Model for Soft Materials
The key limiting factor turned out to be yield stress. This is the amount of pressure needed to make bubbles rearrange. Once this threshold is reached, liquid escapes. This fresh model aligns with real-world behavior and replaces decades of assumptions. The team hopes their work inspires better foam-based products and deeper insights into soft-matter physics.
