Critical pressure asymmetry in the enclosed fluid diode

TL;DR

This paper investigates how chemical gradients in conical pores can optimize the pressure difference needed for fluid to flow in one direction, enhancing the design of passive fluid diodes for various applications.

Contribution

It introduces a method to calculate Laplace pressures in conical pores with chemical gradients, revealing how to maximize pressure asymmetry for fluid diode efficiency.

Findings

Chemical gradients increase critical pressure difference

Optimal pore geometry enhances unidirectional flow

Design guidelines for efficient fluid diodes

Abstract

Joint physically and chemically pattered surfaces can provide efficient and passive manipulation of fluid flow. The ability of many of these surfaces to allow only unidirectional flow mean they are often referred to as fluid diodes. Synthetic analogues of these are enabling technologies from sustainable water collection via fog harvesting, to improved wound dressings. One key fluid diode geometry features a pore sandwiched between two absorbent substrates, an important design for applications which require liquid capture while preventing back-flow. However, the enclosed pore is particularly challenging to design as an effective fluid diode, due to the need for both a low Laplace pressure for liquid entering the pore, and a high Laplace pressure to liquid leaving. Here, we calculate the Laplace pressure for fluid travelling in both directions on a range of conical pore designs with a chemical gradient. We show that this chemical gradient is in general required to achieve the largest critical pressure differences between incoming and outgoing liquids. Finally, we discuss the optimisation strategy to maximise this critical pressure asymmetry.