Johns Hopkins Whiting School of Engineering 1996 Annual Report [text version]

Whiting School of Engineering 1996 Annual Report

Chemical Engineering
New Chair Launches Polymer Research in Space with Down-to-Earth Experiments
A Magnetic Attraction
Department Facts

New Chair Launches Polymer Research in Space with Down-to-Earth Experiments
Chemical engineering has the distinction of being one of the oldest engineering disciplines at Johns Hopkins. In January 1996, Professor Michael Paulaitis arrived to lead the department as its new chair. In his role, Paulaitis faces the challenges of guiding a dynamic and highly productive young faculty while teaching and managing a thriving research program.

Paulaitis’ research interests include high-pressure phase equilibria; supercritical fluids; computational molecular thermodynamics; and solution properties of polymeric materials and proteins. One of his current projects examines how the phase separation of polymer solutions can be manipulated in a low gravity or microgravity environment. Polymers, the molecular building blocks of plastics, synthetic fibers, adhesives, and paints, are long chains formed by connecting or polymerizing smaller molecules called monomers. In the polymerization process, the newly-formed polymers can precipitate from the solution once the polymer chains become long enough. That is, the polymers and monomers will separate into two phases as a result of polymerization. In many cases, it is desirable to avoid this and continue the polymerization process in order to produce a polymer with particular material properties. One way to control phase separation of polymers and monomers is to form stable suspensions of the two phases. However, creating these suspensions can be difficult. One method to accomplish this is to remove the effect of gravity, since gravity promotes phase separation by causing the polymer phase, which has high density, to quickly settle from the phase containing monomers, which has a lower density. Therefore, stable suspensions will be much easier to form in the microgravity environment of space.

Funded by NASA, Paulaitis and colleague Professor Eric Kaler at the University of Delaware have found a way to mimic low-gravity conditions of space in earth-bound experiments. Combining water, supercritical carbon dioxide, and a surfactant under pressure, the researchers create a solution that forms two phases with the same density. The two phases do not readily separate and actually form a unique environment for polymerization processes. Over the next four years, Paulaitis and Kaler will study the characteristics of these suspensions and try to create novel polymers in them. “One appealing feature of the research for NASA is that this complex behavior can be studied on earth before attempting more time-consuming and expensive experiments in space,” Paulaitis explains.

Paulaitis comes to Hopkins from the Center for Molecular and Engineering Thermodynamics, part of the Department of Chemical Engineering at the University of Delaware. He received a Ph.D. in chemical engineering from the University of Illinois in 1976. Paulaitis has received a number of awards, including an Alexander von Humboldt Fellowship in 1983 and a Presidential Young Investigator Award in 1984. In 1994, he became a member of the Academy of Sciences of Technological Cybernetics of the Ukraine.

A Magnetic Attraction

Most of us associate polymers with plastic, but that’s not the case with Assistant Professor Denis Wirtz. “Biological macromolecules such as DNA, RNA, and proteins are all polymers in the sense that they are huge molecules containing sequences of the same subunit,” Wirtz says. In studying the properties of a particular type of DNA, Wirtz has developed a technique that allows him to micromanipulate the building blocks of life.

“The DNA molecules I use measure 17 microns from end to end and can be viewed with a simple benchtop microscope,” Wirtz explains. He combines a dilute concentration of fluorescently labeled DNA with a similar batch of unlabeled DNA. To this mixture he adds tiny magnetic beads that are .01 microns in size. These beads, loaded with iron oxide, wear a fluorescent protein and a protein called biotin. The biotin attaches to one of the two ends of the fluorescent DNA. With the help of an electric current and a joystick—the same type that’s used in computer games—Wirtz has a three-dimensional micromanipulator.

Wirtz’s technique has a tweezers effect because the magnetic beads can be pulled, with the DNA attached. “In this way, the micromanipulator also becomes a quantitative tool,” Wirtz says. “Once you know the strength of the force you apply to a bead, you know the force. With the particle tracking software we wrote, we can measure the velocity of the bead. It turns out that—by definition—force over velocity is the friction coefficient of the object you’re moving.” In that sense, Wirtz’s research has yielded the first direct measurement of the friction coefficient of a single macromolecule. The technique is an improvement over “optical tweezers,” a method that attaches to the DNA a glass bead of high polarizability, which can then be attracted to a region of large (optical) electric field. Wirtz’s next project is to give his microscope a different set of eyes and record DNA movement through a camera and transfer it into the computer, creating a digitized “movie.” “With this procedure we can study DNA’s coil-stretch transition property, first predicted 20 years ago,” he comments.

Wirtz’s research has potential applications in more effective drug design and delivery. “You can use these magnetic tweezers to transport a vesicle containing a substance to a tiny targeted area in the body. The tweezers can even open the vesicle, releasing its cargo of antibodies, proteins, or disease-fighting drugs,” he comments. Non-medical uses extend to automobiles, where the application of a magnetic field could create “smart fluids” in brakes and shock absorbers. Wirtz recently received a grant from the Whitaker Foundation to continue his groundbreaking research in this area.

Established 1936
Chemical engineering is a descendant of the Department of Gas Engineering, established in 1924.

Phone 410-516-7170

Email che@jhu.edu

WWW http://www.jhu.edu/~cheme/

Students
1995-96 Academic Year
Graduate: 40
Undergraduate: 102

Faculty and Researchers
Michael E. Paulaitis, Chair
Timothy A. Barbari
Michael J. Betenbaugh
Marc D. Donohue
Michael Karweit
Joseph L. Katz
Mark A. McHugh
Kathleen Stebe
John H. van Zanten
Denis Wirtz

Research Areas
Biochemical Engineering
Biomedical Engineering
Complex Fluids
Computational and Molecular Thermodynamics
Interfacial Phenomena
Membrane-Based Separations
Nucleation Processes
Polymer Science
Recombinant DNA Technology
Supercritical Fluids
Surfactant Phase Equilibria and Dynamics
Surfaces and Interfaces

Chemical Engineering New Chair Launches Polymer Research in Space with Down-to-Earth Experiments A Magnetic Attraction Department Facts

Chemical Engineering
New Chair Launches Polymer Research in Space with Down-to-Earth Experiments
A Magnetic Attraction
Department Facts