Capillary Pumping Independent of Liquid Sample Viscosity

Abstract

Capillary flow is a dominating liquid transport phenomenon on the micro- and nanoscale. As described at the beginning of the 20th century, the flow rate during imbibition of a horizontal capillary tube follows the Washburn equation, i.e., decreases over time and depends on the viscosity of the sample. This poses a problem for capillary driven systems that rely on a predictable flow rate and where the liquid viscosity is not precisely known. Here we introduce and successfully experimentally verify the first compact capillary pump design with a flow rate constant in time and independent of the liquid viscosity that can operate over an extended period of time. We also present a detailed theoretical model for gravitation-independent capillary filling, which predicts the novel pump performance to within measurement error margins, and in which we, for the first time, explicitly identify gas inertia dominated flow as a fourth distinct flow regime in capillary pumping. These results are of potential interest for a multitude of applications and we expect our results to find most immediate applications within lab-on-a-chip systems and diagnostic devices.

Capillary pumping independent of the liquid surface energy and viscosity

“…As outlined in previous studies 1 , capillary flow is a dominant liquid transport phenomenon at the microscale and nanoscale. Capillary flow modification is used in many applications, e.g., to manipulate liquids in heat pipes 2 , to regulate fluid flow in low-gravity environments in space 3 , to pattern biomolecules on surfaces 4 , in the pumping mechanism of immunoassays 5 , and in diagnostic applications 6 .…”

“…Capillary flow and its control have been the subjects of extensive research since the beginning of the twentieth century. After a short initial acceleration phase, the flow in capillary pumps is defined by the capillary pressure drop over the liquid–gas interfaces and the viscous losses in the transported fluids 1,18 . In capillary devices with constant cross-sections, this leads to the well-known Washburn behavior, which is characterized by a flow rate that depends on the square root of time 19–21 .…”

Challenges and opportunities in blood flow through porous substrate: A design and interface perspective of dried blood spot

“…Such deviation from Lucas-Washburn capillary filling is due to the occurrence of gas inertia dominated flow. They have also proposed a theoretical model to design such systems as per the applications involving different liquids [102]. They also suggested modifications in the design when a device comprises of a channel connected to an absorbent pad through an intermediate liquid separator.…”

Capillary pumping with a constant flow rate independent of the liquid sample viscosity and surface energy

“…Constant capillary flow can be obtained by introducing a large up-stream liquid resistance that dominates the viscous losses in the capillary device [6,7]. Constant and sample viscosity independent capillary pumping can be obtained by introducing a downstream fluidic resistance for the displaced air that dominates the viscous losses in the capillary system [8]. Capillary pumping independent of sample surface energy has not been reported previously.…”