Stetten Amy Z, Treece Bradley W, Corcoran Timothy E, Garoff Stephen, Przybycien Todd M, Tilton Robert D
Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Colloids Surf A Physicochem Eng Asp. 2018 Jun 5;546:266-275. doi: 10.1016/j.colsurfa.2018.03.003. Epub 2018 Mar 2.
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.
传统上，界面被定义为不混溶相之间的边界。然而，先前的研究表明，即使两种流体完全互溶，它们在很长一段时间内仍会保持一个可检测到的“有效界面”。互溶界面已在各种两种流体的系统中进行了研究，它们之间有一个单一的边界。然而，这项工作尚未扩展到置于互溶池顶部的液滴的三相系统。我们表明，这些三相系统遵循与不混溶系统相同的润湿条件，并且它们的液滴形状遵循扩展的杨-拉普拉斯方程。随着时间的推移，互溶界面会扩散，液滴的形状也会演变。我们将2微升水滴置于互溶的聚丙烯酰胺溶液之上。液滴被下层完全润湿，然后在表面下方仍可被检测到许多分钟。使用毛细管数，初始有效界面张力可近似为0.5 mN/m量级。水和聚丙烯酰胺在所有浓度下都完全互溶，然而，从侧面看，液滴保持着毛细管形状。对这种行为的研究对于理解互溶聚合物相之间的有效界面非常重要，这种界面在自然界中普遍存在。
