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

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.

Impact of Different Saccharides on the In-Process Stability of a Protein Drug During Evaporative Drying: From Sessile Droplet Drying to Lab-Scale Spray Drying

“…For other polymers it has been observed, that increased solid concentrations of these type of excipients, led to phase separation and increased aggregation in the protein rich phase [ 53 , 54 ]. Furthermore, this phase separation during sessile droplet drying, caused by DEX and other species of high molecular weight, has been elucidated recently [ 55 ]. In the latter work, the authors showed that DEX has a tendency to accumulate at the contact line between droplet and surface, whereas other species of high molecular weight, like polyethylene glycol, rather show a tendency to stay at the droplet centre [ 55 ].…”

Drying of bio-colloidal sessile droplets: Advances, applications, and perspectives

“…[221]. A simple bio-mimetic colloidal solution, dextran-polyethylene glycol, deserves attention for examining the phase separation in the drying droplet by tuning their initial concentrations, leading to a change of wettability and compatibility [222]. Recently, a concentration-driven phase transition has been found when diluted human blood droplets and a high concentration of BSA droplets are dried under ambient conditions [31].…”

Recent progress in primitive polyester synthesis and membraneless microdroplet assembly

“…Nevertheless, another possibility could be through macromolecular self-assembly, which was absolutely essential to the origins of life [54][55][56]. However, macromolecular self-assemblies could take many forms, for example droplets [57,58], crystals [59,60], fibers [61,62], or even more complex architectures [63,64]. However, one type of macromolecular selfassembly likely to have been relevant for origins of life were primitive compartments, also known as protocells, which themselves may have eventually evolved into modern cells (although it is not a strict requirement) [65][66][67].…”