Capillary filling in microchannels patterned by posts

TL;DR

This paper studies how surface patterning with posts affects capillary filling in microchannels, revealing that pinning and channel geometry critically influence the filling process, with a threshold contact angle around 55 degrees.

Contribution

It demonstrates the role of posts and channel height in controlling capillary filling, highlighting the importance of surface patterning and geometry in microfluidic design.

Findings

Pinning on post edges can halt filling.

Filling depends on contact angle and channel height.

Filling occurs for contact angles less than ~55 degrees in tall channels.

Abstract

We investigate the capillary filling of three dimensional micro-channels with surfaces patterned by posts of square cross section. We show that pinning on the edges of the posts suppresses, and can halt, capillary filling. We stress the importance of the channel walls in controlling whether filling can occur. In particular for channels higher than the distance between adjacent posts, filling occurs for contact angles less than a threshold angle \sim 55 deg., independent of the height of the channel.