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October 27, 2003

For more information on these science news and feature story tips, contact the public information officer listed at (703) 292-8070. Editor: Josh Chamot

Researchers Create "Smart," Switchable Surfaces
Molecular coating could aid nanoscale assembly, microfuidics

Materials researchers at Iowa State University, working in part under a grant from the National Science Foundation, have demonstrated a novel coating that makes surfaces "smart"—meaning the surfaces can be switched back and forth between glassy-slick and rubbery on a scale of nanometers, the size of just a few molecules.

Possible applications include the directed assembly of inorganic nanoparticles, proteins, and nanotubes, and the ultra-precise control of liquids flowing through microfluidic devices that are finding their way into biomedical research and clinical diagnostics.

The new coating is a single layer of Y-shaped "brush" molecules, according to principal investigators Vladimir V. Tsukruk and Eugene R. Zubarev, lead authors on a report of the work in the September 16 issue of the journal Langmuir.

Each molecule attaches to the surface at the base of the Y, which forms a kind of handle for the brush, and extends two long arms outward to form the bristles. The coating can be switched because one arm is a polymer that is hydrophilic, or attracted to water, while the other is a polymer that is hydrophobic, or repelled by water.

Thus, say the researchers, when the coated surface is exposed to water, the molecules collapse into a series of mounds about 8 nanometers wide, with the hydrophilic arms on top shielding the hydrophobic arms inside. Conversely, when the surface is treated with an organic solvent such as toluene, the surface spontaneously reorganizes itself into mounds that have the hydrophobic arms on top.

Not surprisingly, the two states are very different when it comes to properties such as stickiness and the ability to become "wet."

In future work, the Iowa State team hopes to coax the mounds into an ordered pattern, instead of the current random scatter, which may allow the researchers to make surfaces that are lubricating in one direction and sticky in others.

NSF Media contact: M. Mitchell Waldrop, (703) 292-7752, mwaldrop@nsf.gov

NSF Program manager: Andrew Lovinger, (703) 292-4933, alovinge@nsf.gov

Principal Investigators: Vladimir Tsukruk, (515) 294-6904, Vladimir@iastate.edu
Eugene R. Zubarev, (515) 294-9465, zubarev@iastate.edu

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NSF Funds a Low-Energy Neutron Source at Indiana University
LENS facility will be powerful tool for analysis and a training ground for students

The National Science Foundation (NSF) has committed approximately $6.4 million to Indiana University over the next three years to build LENS, the Low Energy Pulsed Neutron Source.

Beams of slow-moving, "cold" neutrons turn out to be a very effective way to probe the structures of molecules and crystals, and have found applications in such fields as drug design and corrosion detection in airplane wings, yet only a handful of neutron scattering research facilities are currently in operation in this country. The new facility helps to fill the research gap and addresses the need for new students to enter the field.

Since LENS's slow-moving neutrons will be produced by low energy protons, there will be minimal contaminant radiation, says principal investigator John Cameron. This factor will make the facility well suited to its on-campus setting, he added.

When completed in 2005, LENS will also be well positioned for use by students and others who want to try new experimental techniques or develop prototype instruments. Indeed, LENS promises to become a significant training ground for the young scientists who will use the Department of Energy's billion-dollar Spallation Neutron Source, a much larger and more energetic neutron scattering facility thatís scheduled for completion in 2006 at the Oak Ridge National Laboratory in Tennessee.

In that sense, says NSF's LENS program manager Hugh Van Horn, "LENS represents a good synergy between NSF's traditional support for university scale research and DOE's support for national-scale facilities."

Additional funding for LENS will come from the state of Indiana, and much of the equipment will be surplus provided by the Air Force and Los Alamos National Laboratory.

NSF Media contact: M. Mitchell Waldrop, (703) 292-7752, mwaldrop@nsf.gov

NSF Program manager: Hugh Van Horn, (703) 292-4920, hvanhorn@nsf.gov

Principal Investigator: John Cameron, (812) 555-9407, cameron@iucf.indiana.edu

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Nanoparticles Make Silicone Rubber Clearly Stronger

Silicone rubber and other rubber-like materials have a wide variety of uses, but in almost every case they must be reinforced with particles to make them stronger or less permeable to gases or liquids. University of Cincinnati (UC) chemistry professor James Mark and colleagues have devised a technique that strengthens silicone rubber with nanoscale particles, but leaves the material crystal clear.

Silicone rubber is often reinforced by tiny particles of silica (the primary component of sand and the mineral quartz). However, those silica particles can cloud the silicone rubber, which is a problem for protective masks, contact lenses and medical tubing that rely on silicone rubber's transparency.

Mark, along with graduate student Guru Rajan, UC professor Dale Schaefer, UC associate professor Gregory Beaucage and Yeungnam University (Korea) professor Gil Sur reported on their new technique in the August 15 issue of the Journal of Polymer Science Part B: Polymer Physics.

The technique infuses silicone rubber with nanoparticles up to five times smaller than the silica particles formed by comparable methods while still providing the same level of reinforcement and maintaining the silicone rubber's clarity.

Variations on the technique might also be used to enhance other properties of silicone rubber and similar materials, affecting such traits as impermeability to gases or liquids. This could lead to better masks or suits to protect against agents that might be used in terrorist attacks.

The team's technique is an improvement over related methods that use a chemical reaction to create silica particles within the silicone polymers. By generating the required catalyst in place from a tin salt and by restricting the amount of water to only that absorbed from water vapor in the air, the silica particles remain smaller—only 30 nm to 50 nm across—and are evenly dispersed throughout the silicone rubber. At that size, smaller than the wavelength of ultraviolet and visible light, the silica nanoparticles are essentially invisible.

NSF Media Contact: David Hart, 703-292-7737, dhart@nsf.gov

NSF Science Experts: Andrew Lovinger, 703-292-4933, alovinge@nsf.gov
Triantafillos J. Mountziaris, 703-292-8371, tmountzi@nsf.gov

Principal Investigators: James Mark, 513-556-9292, james.mark@uc.edu
Gregory Beaucage, 513-556-3063, gregory.beaucage@uc.edu

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