Friction at a distance, the friction between close objects that
aren't in contact, is poorly understood. Seppe Kuehn and his
colleagues at Cornell have set out to change this.
First, what does
contact mean? Kuehn (607-254-4685, email@example.com) suggests that
when two objects are less than about 1 nanometer apart they are said
to be in contact. One can think of contact friction as being a sort
of micro-velcro process -- atomic "hills" in one surface scrape past
atomic "valleys" from the other surface. To observe non-contact
friction, the friction between two surfaces separated by more than 1
nanometer, the Cornell researchers use a tiny single-crystal
microcantilever less than a millimeter long and only a few thousands
of atoms thick.
Brought vertically downwards toward a surface, and set in motion,
the cantilever will slow down in proportion to the friction it feels
from the surface beneath. Surprisingly, the friction force between
the cantilever and sample depends on the chemistry of the sample.
By studying this dependence of non-contact friction on the chemistry
of the sample the Cornell scientists have made the first direct,
mechanical detection of non-contact friction arising from the weak
electric fields caused by motions of molecules in the samples.
The samples included various polymer materials.
This work is motivated
by recent efforts towards single-molecule MRI which require the
detection of very small forces -- efforts that have been hindered by
Kuehn, Loring, and Marohn,
Physical Review Letters, 21 April 2006
Contact Seppe Kuehn, Cornell University, 607-254-4685, firstname.lastname@example.org