‘Weak’ physical forces measured for first time
31 May 2016 by qmcqmmjcbp.d qmcqmmjcbp.d
Individual van der Waals forces between individual atoms have been measured for the first time by scientists at the University of Basel.
Individual van der Waals forces between individual atoms have been measured for the first time by scientists at the University of Basel.
Together with physicists from the Swiss Nanoscience Institute, they achieved this feat using atomic force microscopy. Weaker than chemical bonds, van der Waals forces act between non-polar atoms and molecules. They are involved in forces causing cohesion, adhesion, friction or condensation and it is these forces that allow geckos to ‘stick’ to almost any surface.
Professor Ernst Meyer, involved in the study, told Laboratory News: “Van der Waals forces are weak, but they play an important role on a larger scale, because they have a longer decay length than covalent forces. Therefore, they have an influence on the mesoscale [micrometre to millimetre range], for example, they play an important role for adhesion.”To measure the van der Waals forces, researchers took a low-temperature scanning force microscope and fixed a single xenon atom to its tip. Single argon, krypton and xenon atoms were then fixed in a ‘nano-beaker’ grid of copper atoms.
Measured and theoretical values were compared and displayed graphically. As expected by the scientists, when the distance between the atoms increased the measured van der Waals forces fell sharply. All the measured forces were larger than had been expected based on the researchers’ calculation. For Xenon, the measured values were found to be up to twice as much as predicted.
Van der Waal forces are caused by ever-changing electrical fields around atoms and molecules, causing dipoles which cause a knock-on effect of redistribution of electrons in other nearby molecules. Due to the dipoles being formed around both molecules, a temporary attraction occurs between them.
Professor Meyer said the next steps would be assembling more complex structures using atom positioning and measuring those van der Waal forces. Other weak forces seen on the atomic scale, such as hydrogen bonding, will be searched for also.
The research was reported in Nature Communications.
