Phase Transition in Polymeric Systems for Biomimetic Materials Working with Water

Inspired by history of natural environment and biomaterials, we are designing and fabricating functional soft materials through organizing polymeric materials [1-3]. To propose advanced energy converting systems, materials living with water are the target. From a viewpoint of biomimetics, the air-water interface is expected to play an important role in establishing a universal model of dissipative structures. Viscous fingering, as an example of nonlinear fluidic flow, is an unstable situation that is widely known as <i>tears of wine</i>. This has been explained through the Marangoni effect, coffee ring effect, Saffman-Taylor instability, etc. However, due to the transitional nature of these phenomena, there are few strategies for immobilizing such fluidically regulated interfaces. Recently, such phenomena have been applied successfully to an immobilized structure by controlling the evaporation of a mixture of biopolymer and water.<br/>In this study, we present a brief discussion of nonequilibrium phenomenon, “meniscus splitting”. More precisely, an air-liquid interface is divided into multiple interfaces to partition a space. By using a mixture of polysaccharides and water, a macroscopic pattern following a specific rule could be confirmed. When the mixture is dried from a top open cell, the polymer forms deposits at specific positions to split the meniscus by bridging a millimeter-scale gap. Because water irreversibly evaporates from the liquid phase to the air phase through a gap, the air-liquid interface is in a nonequilibrium state between polymer deposition and water evaporation. The interfacial instability is comparable to the mechanical instability of gels at the phase transition or to the skin layer of gel surfaces during shrinking. Furthermore, by controlling the deposition, the polymeric self-assembly could acts as vapor-sensitive materials or super moisturizing materials [1-2]. Here, the phenomenon and the material’s behaviour would be discussed from physicochemical viewpoints.<br/>References: [1] I. Saito, L. Wu, K. Okeyoshi, et al,<i> ACS Appl Polym Mater</i> 4, 7054 (2022). [2] K. Budpud, K. Okeyoshi, et al, <i>Small</i> 16, 2001993 (2020). [3] K. Okeyoshi, et al:<i> Angew Chem Int Ed</i> 58, 7304 (2019).