Emergence and Growth Dynamics of Wetting-induced Phase Separation on Soft Solids

Liquid droplets wetting soft gels often induce capillary ridges at contact points, where local ridge profiles are governed by the balance of surface stresses [1]. However, the inherent stress singularity at contact points poses challenges for classical mechanical theories to model soft wetting responses. In addition, wetting-induced phase separation has been poorly understood both theoretically and experimentally [2]. To address these challenges, we performed in-situ visualization of the wetting profiles on soft polymeric gels using dual-wavelength confocal microscopy [3]. We experimentally demonstrate that the emergence of phase separation effectively overcomes the elastic singularity at contact points. Using Onsager's variational principle, we proposed a phenomenological model that effectively captures the growth dynamics of phase separation, including a transition from a transient diffusive state to a long-term equilibrium state. Comparing experimental results with theoretical predictions, we reveal how the intrinsic material parameters of soft gels dominate the dynamics of phase separation at different crosslinking densities.