Slip effects in a dewetting polymer microdroplets

A non-equilibrium liquid drop sitting on a smooth substrate will contract or spread depending on the equilibrium contact angle and the initial shape of the drop. Previous studies assume a huge separation of length scales between the drop contact size $R$ and the slip length $b$ (typically $b/R$ = 10$^{-6}$-10$^{-5}$). One well known example is that of a drop spreading over a completely wetting surface, which follows Tanner's law. In this study, we experimentally and theoretically investigate contractions of microscopic droplets in regimes where these two length scales are not widely separated ($b/R$ = 10$^{-2}$-1). These regimes become relevant in micro- and nano-fluidic systems. Instead of a quasi-static spherical shape during the evolution, the profiles display more complex shapes in these regimes. We find that: 1) the interface profile near the contact line evolves in a self-similar way in the early stage; 2) depending on $b/R$, the profile can develop a characteristic bump shape in the intermediate stage of the evolution. 3) at late times, the radius saturates exponentially with a certain time scale, which depends on the slip length.