Nanoscale forces solve puddle problem

Scientists have discovered that the forces responsible for stopping a liquid from spreading on a solid surface only act at the nanoscale.

A research team at the Massachusetts Institute of Technology (MIT) observed thin-films of liquid touching a solid surface at a molecular level and found that intermolecular forces between the liquid-solid and the liquid-air interface stopped the liquid spreading.

“What’s striking here, what’s actually stopping the puddle is forces that only act at the nanoscale. These are the missing intermolecular forces in the macroscopic description. Properly accounting for these forces resolves the previous paradoxes,” said research associate Amir Pahlavan.

Earlier models of liquid-film propagation don’t account for the spread of the liquid coming to an end.

“The classic thin-film model describes the spreading of a liquid film, but it doesn’t predict it stopping. Within a macroscopic view of this problem, there’s nothing that stops the puddle from spreading,” said Pahlavan.

In the study, published in the journal Physical Review Letters, the team experimented with liquid flow on perfectly smooth surfaces and observed how molecular forces act when a liquid touches a solid surface.

The researchers believe that these findings could be used in the design of microchips and lubrication of gears and machinery. Next, the team will extend the analysis and study the way fluids flow over rough surfaces. They believe that this will help studies of fluids in underground formations.

“This work puts us in a position to be able to better describe multiphase flows in complex geometries like rough fractures and porous media,” said research leader Dr Ruben Juanes.

Paper: http://juanesgroup.mit.edu/publications?action=AttachFile&do=get&target=pahlavan_etal_prl_2015.pdf