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« Room Temperature Nano Machines | Main | The Ethics of Killer Robots »

February 19, 2009

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Dan S

Thanks for the very interesting posts. It raises several questions.
1. As far as I understand Drexler now advocates usage of materials with large lattice constant (i.e. relatively large building blocks). But this will result in increase of volume of functional devices. Wouldn’t this seriously affect operating speed of nanomachines and possibly other parameters?
2. Regarding using silica instead of diamond, I can see a number of problems:
- Amorphous silica is not particularly stiff (Young modulus of about 30-60 GPa, compared to 1200 GPa of diamond).
- Silica in water is prone to hydrolysis.
- Oxygen diffusion in silica can cause damage to machines made of silica
- It is difficult to imagine how machine made of pure silica can made more silica by mechanical positioning.

Chris Phoenix

Operating speed and power density and build time scale inverse-linear to the size. (Relative throughput scales as the fourth power if you hold material constant; linear if the chunk size scales with device size.)

The silica problems may or may not be showstoppers. First, I wouldn't expect a *pure* silica machine to make more - but occasional "vitamins" are allowed if they can be synthesized by traditional chemistry. So, for example, make a machine that has a binding pocket for an enzyme that mediates deposition of silica.

Some enzymes don't need water to work. It would require research to find a version of a silica-deposition enzyme that worked in e.g. supercritical CO2. I don't know if such a thing exists or can be built... but I suspect there's some combination of solvent and enzyme that would reduce the hydrolysis problem.

Once you're not using water, you can cool things down a bit. (Lots of solvents seem to freeze at lower temperatures - maybe because they're less polar?) Cooler temperatures should help with stiffness and oxygen diffusion.

So... thanks for your questions... I hadn't really thought about solvents other than water for silica building, but now I think it's quite possibly the way to go.

Chris

x-ray fluorescence

Nanomechanical systems designed to trap and release molecules from pores in response to a stimulus have been the subject of intensive investigation, in large part for their potential applications in precise drug delivery. Nanomaterials suitable for this type of operation must consist of both an appropriate container and a photo-activated moving component.

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