Scientists Rein In Fractious Friction
Autos may get longer life, while computer chips get smaller
ANN ARBOR, MICH. — Imagine driving a car for 20 years and still hearing the original engine purr. Or buying a set of knives that really never needed sharpening.
Don't reach for your credit card yet. But recent progress in the field of friction might soon bring these developments to consumers in nearly every market.
Friction exists everywhere surfaces meet. That's been widely understood, at least writ large, since Leonardo DaVinci.
What's less clear is how microscopic friction - interactions between individual atoms - leads to macroscopic effects like the intense heat generated by a churning automobile engine, the way a skate blade melts the ice it rides over, or why that mug sits patiently on your kitchen table while you're reading this article instead of sliding off at the merest nudge.
Mark Robbins, a physicist at Johns Hopkins University in Baltimore, studies tribology - friction, lubrication, and wear. The science has had a major growth spurt in the last decade thanks largely to breakthroughs that allowed researchers to measure forces affecting individual atoms.
"Eventually, molecular motions lead to the macroscopic behavior that we observe," he says. "But there's a lot of physics that happens on the way."
In the late 1920s, physicists hypothesized, but couldn't prove, that some solids could move across another solid without any friction. Only within the last decade, however, have microscopes become sensitive enough that researchers can "see" - by gauging the forces they exchange - single atoms jostling their neighbors.
About three years ago, Dr. Robbins and his colleagues began pairing their computer models with atom-level experiments by researchers in Boston and Japan. They found that, contrary to the visible world, where solids require a strong push to overcome immobility - try shoving a sofa across the floor - microscopic surfaces slide at the slightest impetus.
Robbins's work indicates that the key to intransigent sofas lies with so-called "third-bodies," minuscule grunge that paralyzes the motion of passing atoms by lodging in their peaks and troughs.
"We cannot understand friction until we recognize that these third-bodies do everything from preventing to accelerating wear," says Irwin Singer, head of the tribology section at the Naval Research Laboratory in Washington.
BEFORE advances in microscopy and computer modeling, Dr. Singer says, trying to fully understand friction was akin to making predictions about next summer's weather using a weather vane today. "Things are going on at that interface [between surfaces] that one could never see but which is more important than the original surfaces," he says.
To keep materials from eroding each other, tribologists use lubricants. Understanding more about how surfaces grate should lead to more effective lubricants - a field Singer says is still young.
Slicker, more-durable lubricants might soon keep cars on the road indefinitely by protecting the pistons and other moving parts from heat damage and other wear. Autos are notoriously inefficient, losing about 60 percent of their energy to heat through exhaust, and 15 percent more to friction, according G. James Johnston, a senior researcher with Mobil Technology Co., a division of the Mobil Corp., in Paulsboro, N.J. Trimming that figure could lead to dramatic improvements in everything from gas mileage to engine longevity.
Already, tribology's blossoming has helped shrink computer chips and expand data storage capacity, says Bharat Bhushan, professor of mechanical engineering at Ohio State University in Columbus.
Further along, Singer envisions "smart lubricants," dormant molecules that can turn on when needed. And even more distant, in what's now the realm of science fiction, developments in tribology might eventually permit pliable robots, like the morphing metal nemesis in the movie"Terminator 2."
But for now, Singer would accept something a little more mundane: "With all that we know about the lubrication of rubber over glass, we still cannot make an inexpensive, squeak-free windshield wiper."