Capillary filling in patterned channels

TL;DR

This paper investigates how microchannel surface patterns like posts and ridges influence capillary filling, revealing that pattern orientation and contact angle critically affect the filling process.

Contribution

It provides new insights into how surface patterning affects capillary filling dynamics, especially the roles of posts and ridges in pinning or enhancing flow.

Findings

Ridges perpendicular to flow cause contact line pinning and slow filling.

Ridges parallel to flow can enhance filling by increasing surface area.

Posts have minimal effect at low contact angles but can pin the front at higher angles.

Abstract

We show how the capillary filling of microchannels is affected by posts or ridges on the sides of the channels. Ridges perpendicular to the flow direction introduce contact line pinning which slows, or sometimes prevents, filling; whereas ridges parallel to the flow provide extra surface which may enhances filling. Patterning the microchannel surface with square posts has little effect on the ability of a channel to fill for equilibrium contact angle $\theta_e \lesssim 30^{\mathrm{o}}$. For $\theta_e \gtrsim 60^{\mathrm{o}}$, however, even a small number of posts can pin the advancing liquid front.