  Liquid droplets on soft solids, such as soft polymeric gels, can induce
substantial surface deformations, leading to the formation of wetting ridges at
contact points. While these contact ridges have been shown to govern the rich
surface mechanics on compliant substrates, the inherently divergent
characteristics of contact points and the multiphase nature of soft reticulated
gels pose great challenges for continuum mechanical theories in modeling soft
wetting phenomena. In this study, we report in-situ experimental
characterizations of the emergence and growth dynamics of the wetting-induced
phase separation. The measurements demonstrate how the migration of free chains
prevents the stress singularities at contact points. Based on the Onsager
variational principle, we present a phenomenological model that effectively
captures the extraction process of free chains, including a crossover from a
short-term diffusive state to a long-term equilibrium state. By comparing model
predictions with experimental results for varied crosslinking densities, we
reveal how the intrinsic material parameters of soft gels dictate phase
separation dynamics.
