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From the Labs: Nanotechnology

New publications, experiments and breakthroughs in nanotechnology–and what they mean.
March 1, 2007

Tough Nanomaterials
Potential applications include tear-resistant fabrics and fuel-saving car parts

Microscopic structures in a new, ultratough material that is reinforced with disc-shaped nanoparticles change shape under stress, altering the way they refract light.

Source: “High-Performance Elastomeric Nanocomposites via Solvent-Exchange Processing”
Shawna M. Liff et al.
Nature Materials 6: 76-83

Results: Researchers have found that using clay nanoparticles to reinforce a polyurethane material makes it 20 times as stiff and twice as resistant to heat. The polyurethane is composed of two different types of monomers–molecules linked up into polymer chains. The monomers don’t mix well, so they locally separate into hard organized regions and soft amorphous regions. A new dispersion process ensures that the nanoparticles preferentially reinforce the hard regions, making the polyurethane stiffer. Since the process also leaves the soft, amorphous areas free to flex, the material can still stretch substantially without breaking.

Why it matters: To date, most attempts to use nanoparticles to stiffen elastomers such as polyurethane have also resulted in undesired decreases in flexibility, which can mean increases in brittleness. The new process not only makes the material stiffer but also makes it much tougher. The material could be used in lightweight, resilient packaging or spun into fibers to make tear-resistant clothing. Or, in an application that takes advantage of its heat resistance, it could replace some metal car body parts exposed to elevated temperatures, such as the hood. The general processing method could also be used to make a wide range of other new elastic materials.

Methods: The process uses two solvents. In one, the clay nanoparticles are dispersed; the other dissolves the polyurethane. The two solvents are then mixed until the suspended nanoparticles spread evenly throughout the dissolved polymer. When the second of the solvents is removed or evaporates, the clay particles are trapped within a tangle of polymer chains. The clay nanoparticles are selected to have a chemical affinity for the crystalline hard structures within the polyurethane, so those are what they preferentially aggregate with, rather than with the soft, amorphous regions.

Next Steps: Reducing the amount of solvent used could make the manufacturing process cleaner and easier. Making actual products from the material may require adjusting manu­facturing techniques: too much heat during processing may reduce the material’s stiffness.

Practical Nanosensors
An easier way to make nanowire sensors and integrate them into electronics could lead to handheld detectors of pathogens, cancer

Source: “Label-Free Immunodetection with CMOS-Compatible Semiconducting Nanowires”
Eric Stern et al.
Nature 445: 519-522

Results: Researchers at Yale University have found an easier way to manu­facture nanowire sensors, and their process is compatible with those used to make computer chips. The sensors can detect small concentrations of proteins about as reliably as previous nanowire sensors could.

Why it matters: Today, detecting biological molecules in ultrasmall concentrations requires tagging them with fluorescent dyes and viewing them through bulky optical readers. Nanowire sensors generate electronic signals rather than optical ones, and they do not require tagging, so they can be much smaller and easier to use. As a result, they could lead to handheld sensors that can screen for faint traces of hundreds of pathogens or for early signs of cancer. The new technique could also make it much easier to integrate nanosensors and the electronics that process their signals on individual chips. Such sensors would be more practical to mass-produce.

Methods: The researchers first created patterns on silicon using conventional lithography; chemical etching then removed the nonpatterned silicon, leaving behind silicon wires. But because the wires were still too thick, the researchers let the etching agent continue to eat away at the material under the edges of the pattern.

Next Steps: The researchers are demonstrating the sensors’ ability to detect different molecules, such as virus particles, DNA, and a wider range of proteins.

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