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 harles Rosenblatt points to something that looks like a do-it-yourselfer’s workbench at the side of the Liquid Crystal Physics and Complex Fluids lab in the Rockefeller Building. Then the CWRU professor of physics and macromolecular science crouches near the workbench with his head tipped to the side. He indicates an opening in the workbench surface that is illuminated by a bright light shining from the end of a cable. “The experiment is inside there.”Just below the opening, two large, snub-nosed metal pieces face each other from the east and west, leaving about a two-inch space between them. These pieces, Prof. Rosenblatt explains, are part of his electromagnet. Within this space, two small metal rods face each other from the north and south, leaving another space not much longer than a cigarette filter between them. I peer at this odd convergence of metal parts, but don’t find what I think I’m looking for. “All I can see is that little glass tube between the rods,” I tell Prof. Rosenblatt, noticing even as I say this that the so-called glass tube is behaving very oddly. It pulses ever so slightly, as if it were a transparent worm pulled taut between the two rods, breathing in quick and nervous gulps. “There is no glass tube,” Prof. Rosenblatt says, amused. “That’s the floating liquid. Neha’s levitating it, using—what, twenty-four and a half amps?” Neha Bhatt—a graduate student in physics who has gotten today’s experiment up and running—nods and steps aside to show me a black and white screen displaying video images of the floating liquid. This isn’t ordinary tap water—it’s been paramagnetized with the addition of a chemical called manganese chloride and is now so attracted to magnetic fields that the electromagnet’s pull can compel it to defy the force of gravity. As Ms. Bhatt bumps up the power of the magnetic field, the floating cylinder of water arches upward. She decreases the amperage, and it sags at the center, as if a foot has stepped on it. She allows the electromagnetic field to oscillate, at first slowly, then faster and faster, until the “liquid bridge” wiggles so furiously that it breaks its connection to the metal rods and flies apart. “Where on Earth would you see this nearly perfect cylinder of water float?” Prof. Rosenblatt asks. “I wouldn’t call it a parlor trick, but we do have fun with it. When you see this water just sitting in the air, it’s a lot different from having numbers come out of your computer or traces show up on your oscilloscope. The traces on your oscilloscope are important, too, but this kind of thing makes you feel like a kid again.” On Weightlessness and Chaucer The work being conducted by Prof. Rosenblatt and his colleagues—Philip Taylor, the Perkins Professor of Physics, and Iwan Alexander, an associate professor of mechanical and aerospace engineering—may or may not have rejuvenating effects on the people who see it, but it is certainly causing excitement in the broad arena of microgravity research. Physical Review Letters has already published one article by the threesome, “Collapse Dynamics of Liquid Bridges Investigated by Time-Varying Magnetic Levitation.” In a recent issue, Discover magazine also covered the team’s experiments. On the other hand, Prof. Rosenblatt and his colleagues believe that what they learn about fluid behavior in a microgravity environment may provide clues for solving a number of concrete problems. For instance, the group began a new series of experiments in April, funded by a $400,000 grant from NASA. In these experiments, they are studying the behavior of liquid bridges and applying their discoveries to life-threatening abnormalities in the flow of fluids that line the lungs. The team’s experiments also shed light on a number of other matters, from the management of fluids in different gravitational environments—whether on the moon, the space shuttle, or Mars—to the manufacture of highly purified semiconductor crystals in weightless environments. Chuck Rosenblatt’s interest in using magnets to levitate fluids dates back more than fifteen years. He had finished his PhD at Harvard University, where he was part of a research team studying liquid crystals. After two years of postdoctoral work at the University of California at Berkeley, he joined the Massachusetts Institute of Technology’s Francis Bitter National Magnet Laboratory in 1980. At that time, the nation’s oil companies were eager to discover new ways of handling crude oil as they found it in the ground, mixed as it is with dirt and other sediments. Prof. Rosenblatt became intrigued with this problem, as the oil-sediment mixture has some similarities to liquid crystals. He mixed together tiny polystyrene balls and water, creating a model system that had properties in common with the oil-sediment mixture, then added manganese chloride and exposed the mixture to a magnetic field. He was surprised to discover that the paramagnetized water was levitating. But at that point, Prof. Rosenblatt was far less interested in airborne water than in liquid crystals, the cigar-shaped molecules with optical properties that can be manipulated by electric and magnetic fields to create the numbers on a digital watch or the images on a laptop screen. He did buy a powerful magnet when he joined CWRU’s faculty in 1987, but only to continue his studies of liquid crystals. The Perfect Sphere Six years ago, Prof. Taylor walked into Prof. Rosenblatt’s office with a suggestion that they use electromagnetism to study the behavior of liquid crystal drops in a low-gravity environment. A British physicist had predicted about twenty years earlier that a drop of liquid crystal would assume a spherical shape if it were in a gravity-free environment. This prediction was based upon a basic law of physics: that all physical systems try to arrange themselves in the least energy-costly position.
Despite the British physicist’s premise, some researchers thought it possible that certain liquid crystal droplets might not have a smoothly rounded surface—instead, the molecules might align themselves in layers that created a ridged surface. If Prof. Rosenblatt’s lab showed that the droplets did create these ridged shapes, Prof. Taylor and graduate assistant Mesfin Tsige (GRS ’01, physics) would then go on to develop mathematical models to explain how the shape of the droplet was related to the structure and interactions among the liquid crystal’s molecules. Ultimately, the experiments would give scientists new information about materials such as soaps and polymers that would have implications for their commercial processing. In 1996, Profs. Rosenblatt and Taylor received a $280,000 grant from NASA to pursue this research. A few months into the experiment, one of Prof. Rosenblatt’s graduate students, Milind Mahajan (GRS ’00, physics), succeeded in levitating a liquid crystal droplet using a superconducting magnet. The droplet hung in the air: a perfect but somewhat disappointing sphere, proving the British physicist’s prediction and therefore offering few fresh insights into the world of liquid crystals. Fortunately, NASA is what Prof. Rosenblatt calls an “enlightened funding agency,” willing to support the scientists in a new but related microgravity pursuit. “They let scientists follow their noses under the assumption that something interesting will turn up,” he says.
In the archives, Prof. Rosenblatt noticed some interesting studies of liquid bridges under microgravity. Liquid bridges themselves are a natural phenomenon that have intrigued people since antiquity. They are the liquid connection between two or more solids, such as the water between sand particles on a wave-soaked beach, the fluid between fibers in a damp cloth, even the momentary connection that forms when you touch your finger to a drop of rain on the window: The drop spreads across your fingertip—a phenomenon called “wetting,” which occurs when the surface tension between two points is low—until your finger moves and gravity makes the drop slide down the glass. These studies reminded Prof. Rosenblatt of his early experiments levitating paramagnetized water, and he realized that electromagnetism offered a valuable new way to study liquid bridges. Other scientists were studying liquid bridges in three basic ways: either in genuinely weightless environments such as spacecraft, or by using drop tubes that create a moment of weightlessness as the material shoots toward the ground, or by using a tank with two immiscible fluids like oil and water, which effectively creates a zero-gravity environment for the water. But these other approaches have limitations: The first is expensive, the second requires that an experiment last no longer than about five seconds, and the third cancels gravity but places other constraints on the bridge. With NASA’s blessing, Prof. Rosenblatt has spent several years levitating liquid bridges with his magnets and, with Profs. Taylor and Alexander, studying the bridges’ resonance and surface tension.
Believe It or Not In the new NASA study, they are particularly interested in dynamic surface tension—how surface tension is affected by changes in the shape of the bridge over time—as the bridge responds to oscillations in the magnetic field. Most research into surface tension has involved static surfaces, but Prof. Rosenblatt’s unique contribution to this field is his ability to analyze surface tension as a liquid expands and contracts. Kristin Ohlson, whose last story for CWRU Magazine was “The Investigator,” in the fall 2000 issue, is a Cleveland writer whose work has been published in the New York Times, Ms. Magazine, Salon.com, and Food & Wine, among many others. Photography by Scott Pease. Images of the liquid bridge courtesy of Prof. Rosenblatt. |
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