Stone, Vicky Joseph Professor of Engineering and Applied Mathematics and associate dean for applied physical sciences and engineering, was in the audience when Bee projected an image of a micrometer-size bubble with a distinctive polygonal geometry. The bubble surface appeared to be faceted with regular pentagonal, hexagonal, and heptagonal domains that intersected to form a soccer ball-like structure. None of the faces spanned more than 50 nanometers.
“Small bubbles on that scale never last because of surface tension – they instantly disappear. What Rodney showed on that screen was extraordinary,” said Stone. “It was impossible; we all thought it was impossible.”
Smaller bubbles have a greater surface tension and a higher gas pressure than larger ones. As a result, larger bubbles usually grow at the expense of smaller ones, which have very short lifetimes.
“I asked him how he created his foams, and he said he used an ordinary kitchen mixer. The next day I went out and bought a kitchen mixer for the lab,” explained Stone.
The experimental study, conducted by SEAS graduate student Emilie Dressaire in collaboration with Unilever colleagues, revealed that when the bubbles were covered with the chosen surfactant mixture, the surfactant molecules crystallized to form nearly impermeable shells over the bubble surfaces.
The resulting shells possessed an elasticity that allowed them to buckle over time into a remarkably regular and stable pattern. Measurements of the microbubbles’ stability extended over more than a year, and the structural integrity of the bubbles held for the entire period.
The authors note that future applications of these microbubbles could significantly extend the lifetimes of common gas-liquid products that experience rapid disintegration, such as aerated personal-care products and contrast agents for ultrasound imaging. ###
Stone’s co-authors are Dressaire and David C. Bell from SEAS and Bee and Alex Lips from Unilever Research and Development. The research was funded by Unilever.
Contact: Michael Patrick Rutter mrutter@seas.harvard.edu 617-496-3815 Harvard University
Tags: Nano or Nanotechnology and Nanotech
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