Design of open systems for meniscus splitting demonstrated using an aqueous polymer solution.

Open systems on the surfaces of soft materials induce dissipative structures such as evaporative self-organization. Based on the viscous fingering phenomena, we demonstrate a meniscus splitting phenomena by evaporating an aqueous solution of versatile polyvinyl alcohol (PVA) solution from a Hele-Shaw cell. To understand it as a universal phenomenon independent of the polymer species, the distinct evolutionary pathways to pattern formation were evaluated, focusing on the interface deformation and directional deposition of the polymer. The PVA solution, which showed a steep concentration-dependent viscosity gradient under a local moderate humidity gradient, was capable of bridging the cell gap for vertical membrane formation. The interfacial shape transformation from one downward concave to multiple upward convex shapes is controllable not only by tuning the physical properties of the polymer but also by conditioning the water evaporating atmosphere. We envision that demonstrations with different cell aperture designs will expand the realization of this phenomenon using other synthetic polymers or chemical species. Such an open system design with humidity tuning is a strategy for exposure to non-equilibrium phenomena using various soft materials, particles, fibers, and networks.