Evaporation Patterns of Dextran-Poly(Ethylene Glycol) Droplets with Changes in Wettability and Compatibility.

Chiho Watanabe,Miho Yanagisawa

doi:10.3390/life12030373

Abstract

The dextran–PEG system is one of the most famous systems exhibiting phase separation. Various phase behaviors, including the evaporation process of the dextran–PEG system, have been studied in order to understand the physicochemical mechanism of intracellular phase separation and the effect of condensation on the origin of life. However, there have been few studies in dilute regime. In this study, we focused on such regimes and analyzed the pattern formation by evaporation. The specificity of this regime is the slow onset of phase separation due to low initial concentration, and the separated phases can have contrasting wettability to the substrate as evaporation progresses. When the polymer concentration is rather low (<5 wt%), the dextran–PEG droplets form a phase-separated pattern, consisting of PEG at the center and dextran ring of multiple strings pulling from the ring. This pattern formation is explained from the difference in wettability and compatibility between dextran and PEG upon condensation. At the initial dilute stage, the dextran-rich phase with higher wettability accumulates at the contact line of the droplet to form a ring pattern, and then forms multiple domains due to density fluctuation. The less wettable PEG phase recedes and pulls the dextran domains, causing them to deform into strings. Further condensation leads to phase separation, and the condensed PEG with improved wettability stops receding and prevents a formed circular pattern. These findings suggest that evaporation patterns of polymer blend droplets can be manipulated through changes in wettability and compatibility between polymers due to condensation, thus providing the basis to explore origins of life that are unique to the process of condensate formation from dilute systems.

Highlights

Evaporation patterns and its condensation process of colloidal suspensions on a substrate have been intensively investigated as fundamental studies for industrial applications, such as ink and printing technologies, as well as daily life phenomena, such as coffee ring pattern, i.e., a circular ring found in coffee stains [1–3]
We found a specific evaporation pattern of a dilute dextran–PEG droplets accompanied with phase separation
This pattern consists of multiple strings of dextran pulled from the initial contact line toward the center of the droplet and a concentrated circle of PEG

Summary

Introduction

Evaporation patterns and its condensation process of colloidal suspensions on a substrate have been intensively investigated as fundamental studies for industrial applications, such as ink and printing technologies, as well as daily life phenomena, such as coffee ring pattern, i.e., a circular ring found in coffee stains [1–3]. These patterns are determined by the local balance between the Marangoni effect and capillary force through the modification of surface tension and viscosity [3,4]. Evaporation patterns with phase separation have not been reported for very low concentrations of polymer droplets

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Conclusion