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.

软材料表面的开放系统可诱导出耗散结构（dissipative structures），例如蒸发自组织（evaporative self-organization）现象。基于粘性指进（viscous fingering）现象，本研究通过从赫勒-肖池（Hele–Shaw cell）中蒸发多功能聚乙烯醇（PVA）水溶液，证实了弯液面分裂（meniscus splitting）现象。为将该现象理解为不依赖聚合物种类的普适现象，本研究聚焦于聚合物的界面形变与定向沉积，评估了图案形成的不同演化路径。该PVA溶液在局部适度湿度梯度下呈现出显著的浓度依赖性粘度梯度，可弥合池间隙以形成垂直膜结构。界面形貌可从单一向下凹面转变为多个向上凸面，其调控不仅可通过调整聚合物的物理性质实现，亦可通过优化水蒸发环境完成。我们预计，采用不同池孔径设计开展演示实验，可利用其他合成聚合物或化学物质实现该现象。这种搭载湿度调控功能的开放系统设计，为利用各类软材料、颗粒、纤维及网络体系实现非平衡现象（non-equilibrium phenomena）提供了一种可行策略。