Quasi-Two-Dimensional Marangoni Convection and Specific Polymer Deposition in Meniscus Splitting Phenomenon

Spontaneous pattern formation in polymer dissipative systems such as Turing patterns is highly valued in material design. However, the process of fixing patterns to the substrate through evaporation strategy involves a complex pathway from equilibrium to disequilibrium and back to equilibrium as the dispersed particles undergo deposition from saturation to supersaturation. Understanding the non-equilibrium process is essential for the advancement of materials innovation and applications. However, because of high viscosity, polymer dispersions have often received limited attention, presenting processing challenges. Inspired by the viscous fingering phenomenon, we use aqueous polysaccharide dispersions to induce stable spatial patterns within Hele-Shaw cells through controlled water evaporation. These spatial patterns effectively formed deposition patterns in the fluids, dividing the space from one into multiple with anisotropic polysaccharides membrane, splitting the meniscus. ^[1,2] In this study, we meticulously tracked the evolving behavior of internal fluids of aqueous polysaccharide dispersion during the evaporation process using the Particle Image Velocimetry method. As the concentration of the dispersion increased, we observed that periodic convection gradually emerged within the cell. At higher concentrations of the dispersions, Brownian motion gradually loses its dominance, and evaporation-induced Marangoni flow under the influence of viscous forces triggers spatial periodic Marangoni convection, taking over as the dominant behavior. This quasi-two-dimensional convection encourages particles to aggregate at specific areas in the dispersion, which supplements the fluctuating flocculation caused by interfacial evaporation. Differing from the Rayleigh–Bénard convection, by the effect of capillary force, this spatial quasi-two-dimensional convection can be immobilized into polymer membranes with self-assembled polysaccharide structure through evaporating. This aggregation effect of convection is not limited to this kind of biopolymer but also can be extended to various functional polymer particles, complementing what has been achieved in assembling particles from fluids using convection fields.<br/><br/>[1] Saito, I., Wu, L., Hara, M., Ikemoto, Y., Kaneko, T., & Okeyoshi, K. <i>ACS Appl. Polym. Mater.</i> 4 (2022).<br/>[2] Wu, L., Saito, I., Hongo, K., & Okeyoshi, K. <i>Adv. Mater. Interfaces</i>, 2300510 (2023).