  Sessile hydrogel drops on rigid surfaces exhibit wetting/contact morphology
intermediate between liquid drops and glass spheres. Using density functional
theory, we reveal the contact forces acting between a hydrogel and a rigid
glass surface. We show that while transitioning from liquid-like to solid-like
hydrogels, there exists a critical hydrogel elasticity which enables a switch
from attractive to repulsive interaction with the underlying rigid glass
surface. Our theoretical model is validated by experimental observations of
sessile Polyacrylamide (PAAm) hydrogels of varying elasticity on glass
surfaces. Further, the proposed model successfully approaches Young's law in
the pure liquid limit and work of adhesion in the glassy limit. Lastly, we show
a modified contact angle relation taking into account the hydrogel elasticity
to explain the features of a distinct hydrogel foot.
