VTT researchers have shown that surface tension on a solid material is
unconnected to the energy required to create a new surface. Consequently,
surface tension on a solid does not exist in its conventional meaning.
It is generally believed that an excess surface tension on a solid material
exists, in similar manner to that on a liquid. This tension is described by
the Shuttleworth equation, which was presented more than 60 years ago and is
considered a fundamental equation of surface thermodynamics. It is believed to
provide the connection between surface tension and surface energy.
Three
years ago, VTT researchers Lasse Makkonen and Kari Kolari, together with
British scientist David Bottomley, revealed in the Surface Science journal
that the Shuttleworth equation is incompatible with the thermodynamic theory.
This was hard to accept by many and provoked a lively discussion in the
scientific literature.
Now Lasse Makkonen has shown
mathematically that the disputed equation reduces to the definition of
mechanical surface stress and has no connection with the energy of creating a
new, unstrained surface. Consequently, the excess surface tension suggested by
the Shuttleworth equation does not exist. The existence and nature of surface
tension on a solid must therefore be sought by molecular dynamics at the
surface layer only.
This new finding by Makkonen was
published in Scripta Materialia this week. The research was funded by the
Academy of Finland.
Link to the publication: Misinterpretation
of the Shuttleworth equation
