Campus & Community

Practical Physics — David Weitz works with real materials on real problems

5 min read

When David Weitz says his experiment is ready to fly, he means that literally. Like into space.

Weitz has had four experiments aboard space flights, including three on the Mir space station and one on the shuttle flight that hoisted an aging John Glenn into orbit. He has a fifth experiment scheduled to fly aboard the International Space Station next year.

That space station experiment means Weitz, who was appointed Gordon McKay Professor of Applied Physics and professor of physics last July, is intently watching Russia’s sputtering efforts to put the station’s main living module into space.

Weitz, an expert in “soft condensed matter,” said he is trying to take advantage of the weightlessness of space to create new materials with new properties. Once created, he said, it would be too expensive to manufacture the materials in space, but researchers could work to duplicate them in laboratories on Earth.

The experiments study colloids, or small particles suspended in solution, to better understand their properties and structure.

In studying soft condensed matter Weitz is examining materials that are easily deformed, or molded, such as gels and pastes. That makes him one of the few physicists studying things on the macro level, rather than at the molecular, atomic, or subatomic level.

Weitz said studying soft condensed matter at the molecular level would miss the point of what he’s interested in, which is not so much the behavior of molecules and atoms as of the material itself.

Weitz uses the example of the foam on top of a glass of beer. Why, he asks, is the foam on a Guinness different from that on a Budweiser? Why is meringue, for that matter, different from whipped cream? The answer to those questions and myriad others like them, have to do with the properties of the bubbles themselves, rather than the molecules that make up the beer, meringue, or whipped cream.

“If you tried to describe that kind of behavior [at the atomic level], you’d be describing things at a level so deep and so complicated you’d never get to the really interesting properties of the substances,” Weitz said. “Almost everything [in soft condensed matter physics] is at a macro scale. That’s what makes it important and interesting, and that’s what distinguishes it from more traditional types of physics.”

Weitz is well known for several breakthroughs in his field, according to Physics Department Chairman David Nelson, Mallinckrodt Professor of Physics and professor of applied physics. Weitz was the first to describe the spidery structures formed by certain colloidal particles, such as soot and small grains of metal, that don’t take regular geometric forms, but rather form irregular fractal patterns.

Weitz also devised a way of seeing through normally opaque objects, such as a cloud or glass of milk, and to provide information about the droplets making up the object, Nelson said.

“People have very few ways to see what’s going on in these complex solutions,” Nelson said.

Howard Stone, Gordon McKay Professor of Chemical Engineering and Applied Mechanics, called Weitz “a breath of fresh air” and said he has given Harvard expertise in an area that was previously underrepresented.

“He is very interactive, very enthusiastic, very energetic,” Stone said. “He believes strongly in collaboration and interaction.”

Experimental Physicist

Weitz came to Harvard from the University of Pennsylvania, where he was a professor of physics since 1995. Before that Weitz spent 17 years as an experimental physicist in industrial laboratories.

Weitz worked as a physicist for Exxon Research and Engineering Co. from 1978 to 1995, serving as the group leader for the Interfaces and Inhomogeneous Materials Group from 1987 to 1989 and as science area leader for complex fluids from 1989 to 1993.

That industrial experience, Weitz said, has given him a definite bent toward working with real materials on practical problems.

“Because I worked in industry, I like the kind of science that impacts practical problems, but that still addresses the fundamental science questions,” Weitz said.

Weitz said he typically has as many as a half-dozen projects ongoing at any one time. He has worked on everything from gels used in women’s deodorant to fibrinogen, a critical substance in formation of blood clots, to the effect of dirt on the lubricating properties of diesel engine oil.

The motor oil study showed that even a small amount of dirt in the oil would change it from predominantly a fluid to a substance that, though it still flows like a liquid, has assumed properties of a solid and has a greatly reduced lubricating capacity.

That information, Weitz said, is important in creating additives to keep oil slippery enough to protect an engine.

Weitz, who grew up in Ottawa, Canada, received a bachelor’s degree in physics from the University of Waterloo in 1973. He became interested in condensed matter physics while working over the summers in laboratories at Canada’s National Research Council.

He first came to Harvard after graduating from the University of Waterloo, earning a master’s degree in physics from Harvard in 1975, and a doctorate in physics from Harvard in 1978.

Weitz is eager to work with graduate students here at Harvard and said it’s important that physics students want to learn and enjoy what they’re doing. Those two qualities are essential because of the hard work physics requires, he said.

For those students who do choose physics, Weitz believes the future is bright. The current technological revolution shows no signs of slowing down, he said, and is at least partly driven by advances in physics.

“Technology is changing really rapidly. What’s driving the technological change is science, and one of these sciences is physics,” Weitz said.