Foams absorb liquids, making them useful for cleaning, oil recovery, and mineral extraction. Scientists used to think their absorption was controlled by osmotic pressure, but real-world tests show they drain faster than expected.
Scientists at Tokyo Metropolitan University discovered that the required drainage height predicted by traditional physics models is far too high. The real limit comes from the pressure needed to shift bubbles, not just osmotic pressure pushing liquid through gaps.
This insight could improve how we use foams in cleaning, oil recovery, and mineral extraction.
Professor Rei Kurita’s team at Tokyo Metropolitan University has uncovered a surprising rule about foam drainage. By creating a diverse range of foams and observing their behavior between transparent plates, they found that drainage height is inversely related to the foam’s liquid fraction—a universal trend independent of bubble size or surfactant type.
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Their study also revealed an “effective osmotic pressure” that determines the absorption limit, significantly lower than traditional models predict based on bubble size and surface tension. This discovery challenges existing assumptions about foam behavior and could lead to better filtration, cleaning, and material science applications.
Researchers used video cameras to examine foam drainage, revealing a surprising discovery: liquid doesn’t just flow through gaps—it rearranges the bubbles themselves. The key factor behind drainage isn’t surface tension, as previously thought, but yield stress—the pressure required to shift the bubbles.
This breakthrough replaces the traditional static view of foam drainage with a dynamic one, where structural changes play a vital role. The findings could lead to better designs for foam-based products and deepen our understanding of soft materials.
Journal Reference:
- Aoi Kaneda, Rei Kurita. Absorptive limits of foams are governed by kinematic coupling between the solution and bubbles. Journal of Colloid and Interface Science. DOI: 10.1016/j.jcis.2025.137746
