Molecular simulations uncover why water nanodrops spread thin on hydrophilic surfaces

Why does water roll off a duck's back but spread on clean glass?

For macroscopic (millimeter-scale) drops, this behavior can be explained using continuum theory.

However, when nanoscale (10–9 mm) droplets spread on surfaces, a force called line tension becomes relevant and mysteriously changes sign.

Questions about the nature of this force and its relevance to water's interaction with surfaces have remained unanswered. ...