4.1 Nanocars and the development of molecular manufacturing  (Page 5/7)

Although C60 is an attractive molecule totest rolling versus sliding motion at the molecular level, there are some disadvantages to its structure. The properties of C60 limit thesynthesis of the nanocar molecule. In particular, the pi bonds of the molecule react with the palladium catalyst to interfere with chassissynthesis. For this reason, the chassis was synthesized first and the C60 wheels were attached last.

The future of nanocar wheels will include the introduction of more controlled synthesis and variable size. Inthe short term, the Tour Group is investigating the use of carborane molecules, spheroid molecules comprised of carbon and boron, to havemore control over the synthesis. They believe the carborane molecules will exhibit more compliant chemistry for their functional needs(figure 6). In the long term, the Tour Group is investigating large, complex organic molecules that are modeled after bicycle wheels withan outer rim and connecting spokes. This bicycle wheel would be made predominantly of carbon and allow for variable size depending on thelength of the spokes and circumference of the rim.

Chassis

The Tour Group addressed these goals in their design of the chassis in several ways (Figure 7). To physicallyattach the wheels to each other, the Tour Group designed a simple four-axle system reminiscent of a car. There are two axles in thefront and two in the back connected to each other by a central shaft. Within the design of the axles, the Tour Group addressed thesecond goal of how to allow free spinning of the wheels. As discussed earlier, the axles are comprised of triple bonded carbon atoms, whichallow for free rotation about the axle, while maintaining linearity with the adjacent axle (figure 4). The spinning of these triple bondsbegins at 30 degrees Kelvin and has been shown to have virtually no frictional hindrance on the system. This is optimal for a preliminaryresearch into rolling motion because it constrains free variables of the system. In other words, because the triple bonds do not addmeaningful frictional forces to the system above 30 degrees Kelvin, all experimental results can be attributed to the chemistry of thewheel and its rolling or slipping interactions with the surface it operates on. Thirdly, the ease with which the nanocars can be resolvedwith an STM was in part dictated by the structure of the chassis. Specifically, the chassis was designed to have a centralshaft longer than the length of the front or rear axles. The nanocar is wider than it is long. This is important in microscopy because itallows the observer to note the orientation and therefore the direction of translational motion of the nanocar. As far as thesynthesis of the molecule, the Tour Group added functional branches to the phenyl groups on the axles and central shaft, which suspend themolecule in solution and allow for better mixing, better reaction, and better yields. These essential goals were addressed to produce aworking nanocar; however, the goal of adding functionality was not described.