Polymer brushes, coatings consisting of densely grafted macromolecules, have
been known to experience an intrinsic lateral compressive stress, originating
from chain elasticity and excluded volume interactions. This lateral stress
complicates a proper definition of the interface and, thereby, of the
interfacial tension. Moreover, its effect on wettability has remained unclear.
Here, we study the link between grafting-induced compressive lateral stress in
polymer brushes, interfacial tension, and brush wettability using
coarse-grained molecular dynamics simulations. A central result is that the
liquid contact angle is independent of grafting density, which implies that the
strength of the compressive stress inside brush has no influence on the
wettability. Interestingly, though the interfacial tensions lack a proper
definition, the difference in interfacial tension between wet and dry brushes
is perfectly well-defined. We confirm explicitly from Young's law that this
difference offers an accurate description of the brush wettability. It is
demonstrated how these results can be explained from the fact that the
compressive stress appears "symmetrically" in wet and dry brushes. We discuss
our findings in the light of autophobic dewetting and point out the connection
to the Shuttleworth effect for wetting on elastomers