Coalescence and mixing of a polymeric drop impacting on a dissimilar, miscible polymeric liquid film

In this paper, we employ direct numerical simulations to study the impact-driven coalescence and mixing dynamics with a polymeric liquid drop impacting on a film of a different but miscible polymer. We consider two specific situations: (1) a PMMA (poly-methylmethacrylate) drop impacting on a film of PVAc (polyvinyl acetate) and (2) a PVAc drop impacting on a film of PMMA. The results consider different Weber numbers (We = 10, 100) and film thicknesses (h = 5 μm, 20 μm). The impact-driven dynamics and the associated mixing for both cases are captured by the time evolution of the velocity field and the volume fraction of the individual liquids, cavity formation, crown formation, generation of the capillary waves, and the evolution of the mixing front. The difference between the two cases stems from the fact that the PMMA drop impacting on the PVAc film spreads as a very thin film (without mixing) on top of the cavity formed on the PVAc film, while PVAc drop, due to having a smaller surface tension than PMMA, impacts the PMMA film and flows over and “engulfs” the PMMA film. This study numerically probes the drop-impact-driven dynamics between a polymeric drop and a film of another polymeric material. In addition to discovering intriguing non-Newtonian fluid dynamics events, the findings point to the attainment of transient structures with vertically separated layers of two polymeric liquids raising the possibility of fabricating novel multi-polymeric-material structures with rapid (photo)curing.