“Lubricating” nanoscale machines?
from the redefining-"fluid" dept.
A Georgia Tech press release at EurekAlert describes work by Feynman Prizewinner Uzi Landman: "Landman's research group has reported on the tendency of lubricant molecules such as hexadecane and other molecular fluids to form highly ordered layers in planes parallel to the motion of the confining surfaces. On size scales that approximate multiples of the molecular width, these layered lubricants appear to increase their viscosity, 'becoming, at equilibrium and at various stages of the sliding motion, liquid-like in the plane parallel to the sliding surfaces and solid-like in the direction perpendicular to the surfaces,' Landman said…'We must find clever ways to harness and control these new behaviors in order to realize the opportunities in nanotechnology." " CP: While we do need to know about fluids at nanoscales, do nanomachines need "lubrication" per se?
March 1st, 2001 at 4:27 PM
MNT and lubricating films
At a minimum, design of the interfaces between nanomechanisms and larger stuff will probably profit from thorough understanding of such.
Not to mention the need for emollients to go with the nanocosmetics.
March 13th, 2001 at 5:09 AM
Surfaces, tribology, nano vs. macro
(Responding to root article; and I originally tried to post this last week, but the Nanodot server was being ornery that day.)
The Merriam-Webster Collegiate Dictionary defines the term "tribology" as "a study that deals with the design, friction, wear, and lubrication of interacting surfaces in relative motion (as in bearings or gears)" (coined 1966).
As I understand it (speaking as a _Science News_ -reading computer programmer, not a mechanical or materials engineer), we macroscale beings use lubrication because our (solid) macroscale parts are covered with microscale irregularities that catch and bind in unpredictable, undesignable ways. The (usually liquid) lubricant separates the surfaces and splits into layers that slide independently across each other. Like everything else in engineering, lubricants were traditionally created by trial-and-error ("our new 10W-30 formulation performs better under thermal breakdown!"), but the tribologists are now exploring the microscopic details, to support rational design.
The Drexler/Merkle gear/shaft/bearing designs (in _Nanosystems_ and online) carefully place the surface atoms so they *don't* bind. They use two techniques (derived from computational simulations): in the direction of motion, aligning the hills of one protruding atomic surfaces with the valleys of the other; and in the end-view, using relatively-prime numbers of atoms (eg 13-17, or 21-25) so there's no radial symmetry in the potential energy function. (Ie, it can't rotate into an energy minimum.)
The 8th Foresight Conference (this past Nov-2000) reported on some work (rollin g/s liding buckytubes across graphene surfaces) that seems to validate this approach.
So, you can design mechanisms that (1) don't need lubrication (analagous to macroscale Teflon coatings, perhaps), and (2) would react badly to any intervening molecule that tried to *be* a lubricant (since the clearances are too tight to permit liquid-layering).
What about biological mechanisms? Proteins are always surrounded by water molecules, which seem to be critical to folding/maintaining their shapes (alternatively stated: proteins can't avoid a hydrous environment, so have evolved to accomodate it); but most protein structures (enzymes, motors, receptors, pores) stretch and flex rather than rotate. Anyone have relevant details about the rotors in ATP synthase and bacterial flagellar motors?
So the question is… why are some researchers concerned about nanoscale lubrication? Yes, many won't be familiar with Drexler et al. Yes, new lubricants might solve problems of MEMS "stiction". Yes, you can get a grant to use your fancy probe microscope to watch sliding lattices. But which (if any) evolutionary approach(es) to MNT will actually *need* lubrication?