Lego building blocks and a chance conversation at a scientific conference have led to a discovery about water droplets on the International Space Station (ISS) with down-to-earth applications that could range from the production of better inkjet printers to more precise techniques for manufacturing polymer fibers and microelectronic devices, and improvements in mass spectrometry.
The fortuitous conversation was between Boris Khusid, professor in the NJIT Department of Chemical, Biological and Pharmaceutical Engineering, and NASA astronaut Donald R. Pettit. Khusid is an expert in electrohydrodynamics, the study of the motions of ionized particles or molecules and their interaction with electric fields and a surrounding fluid. A Ph.D. chemical engineer, Pettit is a veteran of two long-duration ISS stays and a space-shuttle mission, as well as a six-week expedition to Antarctica in search of meteorites. He is also an energetic advocate of science education at all levels.
As for the Legos, Pettit used them in 2012 during off-duty time on the ISS as components for a Van de Graaff generator, along with a rubber band and an electric drill. Long a staple of basic-science demonstrations, the electrical charge created by the generator’s spinning belt — in this case the rubber band — is strong enough to create a significant air-gap-jumping spark. Pettit documented this combination of mechanical ingenuity and scientific principles in a 2012 online video episode of Physics Central’s “Science of the Sphere.”
Having created the Van de Graaff generator, Pettit tried electrifying minute amounts of water to see how charged droplets would behave in the microgravity environment of the ISS. It was an experiment that put the astronaut, Khusid and several NJIT colleagues on the path to co-authoring a paper published in 2015 in Physical Review Letters: “Detection of a Dynamic Cone-Shaped Meniscus on the Surface of Fluids in Electric Fields.”
A Tale of Taylor Cones
The conical surface shape that forms when water and other liquids are electrified, accompanied by spontaneous sparks and fluid ejection, has fascinated scientists for centuries. This ubiquitous phenomenon, named a Taylor cone after the 20th-century researcher Sir Geoffrey Taylor, is observed in rain drops and lightning. It is also basic to wide-ranging applications, from electrostatic spray guns to medical diagnostics and nanotechnology. However, evolution of the liquid surface from a rounded shape to a cone was a long-standing puzzle in this well-studied phenomenon, as it overlaps spontaneous liquid ejection.
Experimenting with water in microgravity, Pettit made a critical observation — the Taylor cones that formed were some hundred times bigger than those that can be created on Earth. After hearing Pettit lecture about this result, Khusid says that he proposed collaboratively integrating data that he had obtained during his NASA-supported investigation related to the development of “lab-on-a-chip” (LOC) devices.
LOC’s operate using extremely small fluid volumes — down to less than picoliters — and can perform comprehensive diagnostic tests of liquids such as blood, urine and saliva much more quickly than conventional testing. The greater understanding of Taylor cones stemming from the collaboration between Pettit and Khusid involved the ability to evaluate the behavior of electrified droplets with cone heights ranging from 0.5 mm on Earth to 5 cm in microgravity.
The knowledge gained about how a round liquid droplet forms a cone has led to the development of an important new technique for controlling cone formation before it becomes a spray. “It will now be possible to control the full transition from a Taylor cone to a spray,” Khusid says. This is the key that the NJIT researchers have found for improving current applications where Taylor cones are the critical element, and for opening developmental doors to even more practical uses.
Removing Gravity’s Mask
Microgravity — the virtually weightless environment of the ISS — provides a unique venue for studying biological, chemical and physical systems. The results achieved with respect to Taylor cones clearly validate the importance of research in such an environment, one that reveals very useful information obscured by the effects of our planet’s gravity.
Khusid is far from a newcomer to research in greatly reduced gravity. Over a decade of NASA-supported research, he has guided NJIT investigators in conducting electrohydrodynamic experiments during parabolic flights on aircraft operated by the space agency that afford about 15 seconds of weightlessness during each 65-second parabola flown. It was data from this research that complemented Pettit’s observations on the ISS and prompted Khusid to suggest what turned out to be a very productive collaboration.
In addition to new understanding of Taylor cones, Khusid’s ongoing research has yielded valuable insights into gas-liquid phase separation in LOC devices and heat transfer in microelectronics that can advance technologies essential for space exploration, among them liquid pumps and electrolytic oxygen generators that operate efficiently and reliably in weightlessness. It’s also the work that Khusid continues to carry out in association with NJIT research scientist and colleague Ezinwa Elele, M.S. ’06, Ph.D. ’11.
Taking Colloid Research Higher
Recently, Khusid was awarded new NASA funding for developing and conducting experiments on the ISS. A multi-year grant providing a minimum of $815,000 will help to support investigation of electric phenomena in colloids. This is one of only eight proposals funded under NASA’s Physical Science Research Program, Advanced Colloids Experiment to study how complex fluids and macromolecules behave in the ideal microgravity research environment of the ISS.
Khusid and his co-investigators will be contributing to an effort focused on manipulation and assembly of colloids. Typically, colloids are a mixture of microscopic solid particles suspended in a fluid medium. Without the masking effects of gravity, particle sedimentation, convection, jamming and other phenomena can be probed much more deeply. The information obtained could be of significant value in many areas, such as liquid-crystal, pharmaceutical and petrochemical science and technology.
Designing the experiment, building the hardware, and transporting it to the ISS will be an international enterprise. The NJIT researchers will apply their NASA funds to defining experimental parameters, providing samples, and directing the construction of some hardware components by NASA contractors. The European Space Agency will have major responsibility for hardware procurement, along with collaborators at European universities. A decision has yet to be made regarding the delivery vehicle.
Khusid emphasizes that the work projected to be in progress by 2018 presents considerable technical challenges. The experimental system, which will enable light-scattering measurements for the first time on the ISS, will have to be completely self-contained and fully automated. It must also be exceptionally robust to withstand the stresses of rocket transport to the ISS, and to meet all the goals of expanding knowledge on a very high scientific frontier.
By Dean Maskevich