Evolution and disappearance of solvent drops on miscible polymer subphases

Abstract

Traditionally, an interface is defined as a boundary between immiscible phases. However, previous work has shown that even when two fluids are completely miscible, they maintain a detectable “effective interface” for long times. Miscible interfaces have been studied in various systems of two fluids with a single boundary between them. However, this work has not extended to the three-phase system of a fluid droplet placed on top of a miscible pool. We show that these three-phase systems obey the same wetting conditions as immiscible systems, and that their drop shapes obey the Augmented Young-Laplace Equation. Over time, the miscible interface diffuses and the shape of the drop evolves. We place 2-microliter drops of water atop miscible poly(acrylamide) solutions. The drop is completely wetted by the subphase, and then remains detectable beneath the surface for many minutes. An initial effective interfacial tension can be approximated to be on the order of 0.5 mN/m using the capillary number. Water and poly(acrylamide) are completely miscible in all concentrations, and yet, when viewed from the side, the drop maintains a capillary shape. Study of this behavior is important to the understanding of effective interfaces between miscible polymer phases, which are pervasive in nature.

Experiments on Marangoni spreading – evidence of a new type of interfacial instability

“…(2011) and Stetten et al. (2018 b ). Theoretical investigations revealed that the presence of mucus affects the interface shape and the surfactant distribution during spreading, as well as rupture of the film if van der Waals forces are present (Matar, Craster & Warner 2002).…”

“…The airway surface consists of a layer of mucin on top of a layer of cilia and tethered macromolecules, whose properties can be described using a viscoelastic model (Stetten et al 2018a). The first experimental investigations in this area are due to Koch et al (2011) and Stetten et al (2018b). Theoretical investigations revealed that the presence of mucus affects the interface shape and the surfactant distribution during spreading, as well as rupture of the film if van der Waals forces are present (Matar, Craster & Warner 2002).…”