Scientist at Work: James Glazier
Anyone who's ever stared at foams atop glasses of beer or soda knows not all bubbles are equal.
Some bubbles are big. Some bubbles are small. Some bubbles grow. Others shrink. Some bubbles pop, while other bubbles persevere, buoyed by forces unseen.
"We run into foams every day," said Indiana University Bloomington Physics Professor James Glazier, who -- among his diverse portfolio of scientific projects -- has studied the physics of frothy materials. "As foams sit around, bubbles seem to get bigger. People assume that's because bubbles are popping. Bubbles do pop, but that's not why other bubbles get bigger. Gas is actually moving continuously from smaller bubbles to bigger bubbles."
Glazier is also the director and founder of the IU Biocomplexity Institute, and an adjunct professor in IU Bloomington's Department of Biology and School of Informatics.
Lest you think the science of foams is trivial, hundreds of papers are published on the subject every year. Why? Control of foaming processes is crucial to production of everything from airplane parts and bed mattresses to bread and ice cream. Foams play a prominent role in the oil and mining industries and in bomb disposal and putting out fires. Knowledge about how bubbles form, why they form, and how foams change over time can be manipulated to improve both the safety and aesthetic qualities of objects we encounter every day.
"People have been studying foams for hundreds of years," Glazier said. "The coarsening of bubbles over time was of interest to the 17th century Irish chemist Robert Boyle. Lord Kelvin studied them at the end of th 19th century. Kelvin's unpublished notebooks at Cambridge show that he was so obsessed with them that he even worked on them while attending the opera and at dinners with Queen Victoria."
Glazier is an expert in biological physics and materials science, scientific fields that integrate physics, chemistry, mathematics, and biology to understand how different types of physical matter behave. Glazier is also an expert modeler -- he adapts theory into working computer programs that help him and his colleagues understand how their scientific ideas match up with the real world. If a computer model reflects reality well, the model can be used to improve, say, an airplane wing so that it is as light and flexible as possible without sacrificing necessary strength.
"Modern foam science began in two dimensions at the University of Chicago," said Glazier, who got his Ph.D. at Chicago after completing and defending his work on -- you guessed it -- foams. "In the 1950s, Cyril Smith at Chicago and the famous mathematician and computer scientist John von Neumann at MIT collaborated to look at foams pressed between plates of glass, and began modeling their coarsening. They showed something really interesting -- that the rate of growth or shrinking of flattened bubbles depended only on the number of sides they had -- the number of bubbles they touched."
The relationship between flattened bubbles' size changes and their number of sides was found to be almost perfectly linear, Glazier said. If a bubble had six neighbors, it usually stayed the same size. Fewer than six neighbors, the bubble got smaller. Seven or more neighbors -- the bubble would grow, and the more neighbors it had, the faster it would increase in size.
"This rule, sometimes called 'von Neumann's law,' is almost true in three dimensions," Glazier said. "But note quite."
Glazier has been studying and modeling bubbles in three dimensions for 20 years, and has found that a bubble's fate depends both on its number of neighbors and its shape.
"Curvature determines the pressure being exerted on the bubble, both from within and without," Glazier said. "Bubbles whose insides have relatively low pressure will grow whereas bubbles with relatively high pressure will shrink. This is not exactly intuitive."
Glazier said he often demonstrates this concept in class, the result of which often gets gasps of surprise.
"What we do is blow up two balloons, one smaller than the other, but not to the point where the rubber is over-strained," Glazier said. "We put a straw between the balloons while holding the balloons' ends shut and ask the class, 'What will happen?' Most of them expect the smaller balloon will get bigger and the bigger balloon will get smaller."
The reverse happens.
"The reason is that the smaller bubble actually contains more pressure than the bigger bubble, and air will always seek to balance the pressure, whenever possible."
Seeing what's going on with foams in three dimensions presents special problems that materials scientists are only now beginning to overcome.
"The problem is basically that there's not much there," Glazier explained. "So technologies we use to see into solid matter are too powerful. Other technologies, like light microscopy, see what's happening near the surface but don't do a good job of seeing deep inside the foam."
Glazier is a member of an international team of scientists based in France, led by Peter Cloetens and Renaud Delannay, which is using x-ray synchrotrons in creative ways to solve the visualization problem.
"It's really an exciting idea, because we're taking advantage of the physics of x-rays to adjust how we interpret the radiation as it comes out the other side," Glazier said. "We are now able to see inside foams that are a few centimeters thick -- a huge improvement."
Glazier has been helping design and run the experiments, which are carried out at the European Synchrotron Radiation Facility in Grenoble, France.
"At one point in my career, I actually stopped studying foams," said Glazier, who is involved in projects in cell biology, biochemistry, and even vertebrate limb development, among others. "I don't expect I'll return to studying foams full-time, but I must say it's been very satisfying to return to the field, which is special to me."