It is common knowledge that friction is everywhere, even in the places where we least take note of it. But over the past 160 years, the difference in frictional activities of different atoms and molecules has always been a puzzle to scientists. To them, it is a riddle of why a group of water molecules on an icy surface would send people and even large heavy items like cars, spinning. In their language, scientists cannot explain why one pair of atoms or molecules would stick together and why a different pair would simple slide and just move with ease.
Mechanical engineer from the Ardonne National Laboratory, Ali Erdemir says that there is a disconnection between the large scale processes of friction that our bare senses can observe, and the small scale atomic level occurrences that produce those larger scale mechanical behaviors. He says that to this point, we still do not understand a lot of things about the everyday phenomenon.
The scientists observed that when two lubricant materials, graphene and diamond-like carbon or DLC, were allowed to glide against each other, the graphene molecules began moving to form "hollow cylindrical scrolls" that helped lower friction coefficient by a lot. This graphene-DLC arrangement, however, showed fluctuations in the friction coefficient as the experiment proceeded. The researchers then found that humidity affected friction in surprising manner, such that humid environments would cause the measured friction coefficient to increase to almost 100 times compared to the values measured in dry environments.
Scientists at the Ardonne National Laboratory have then used Mira supercomputer, one of the world's fastest supercomputers, to simulate superlubricity, a condition of matter where friction is nearly zero. They found that the graphene nanoscrolls were unstable, which explained the fluctuating values of the friction coefficient. With their idea to incorporate nanodiamond particles into the simulations, the hard material helped stabilize the nanoscrolls.
The researchers believe that superlubricity is a highly desirable property of matter. This would help in energy conservation especially in applications with automobiles, considering that as of the moment, almost one-third, a great fraction, of the fuel tank is consumed in overcoming friction. Materials with superlubricity would definitely increase the life of mechanical components in cars and in other equipment, where necessary, that easily wear down because of friction.
