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Nanocars Taken For a Rough Ride

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Molecules that alight on a surface used to test nanocars look more like obstacles, according to researchers at Rice University and North Carolina State University testing the mobility of single-molecule cars in open air. (Image Credit: Rice/North Carolina State)

Rice University researchers who developed the first nanocars and colleagues at North Carolina State University found in recent tests that driving their vehicles in ambient conditions – exposed to open air, rather than a vacuum – got dicey after a time because the hydrophobic single-molecule cars stuck to the “road” and created what amounted to large speed bumps. The work by Rice chemist James Tour, NC State analytical chemist Gufeng Wang and their colleagues came as Rice prepares to take part in the first NanoCar Race in Toulouse, France, in October. Rice researchers are members of one of five international teams that plan to enter the competition. Just like in the macro world, driving conditions are important for moving nanocars. Though the race will be run in an ultra-cold vacuum, the Rice researchers thought it wise to study how their latest model of nanocars would fare in a more natural setting. “Our long-term goal is to make nanomachines that operate in ambient environments,” Tour said. “That’s when they will show potential to become useful tools for medicine and bottom-up manufacturing.” The newest generation of Rice nanocars features adamantane wheels that are slightly hydrophobic (water-repellent). Tour said some hydrophobicity is important to help keep the nanocars attached to a surface, but if the tires are too hydrophobic, the cars could become permanently immobilized. That is because hydrophobic things tend to stick together to minimize the amount of surface area that is in contact with water. Things that are hydrophilic, or water-liking, are more amenable to floating freely in water, Tour said. In the latest Rice tests with the new tires, the nanocars were placed on surfaces that were either clean glass or glass coated with the polymer polyethylene glycol (PEG). Glass is the most frequently used substrate in nanocar research. Tour said the PEG-coated glass slides were used for their anti-fouling – nonsticky – properties, while the clean glass slides were treated with hydrogen peroxide so the hydrophobic wheels wouldn’t stick. He said the cars weren’t so much being driven as undergoing “directed diffusion” in the tests. The point, he said, was to establish the kinetics of nanocar movement and understand the potential energy surface interaction between the car and surface over time.