What is reverse capillary action?

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In this blog, we will get an overview of reverse capillary action
Let’s begin with the definition

What is reverse capillary action?

Reverse capillary action refers to the phenomenon where a liquid is prevented from rising or even pulled downward in a narrow space (like a capillary or small tube), opposite to what normally happens in regular capillary action.

For example:

Imagine you have a tiny straw and you dip it into a glass of water. What happens? The water climbs up a little inside the straw, right? That’s called capillary action. It’s like the water is saying, “Ooh, I like this straw! I want to climb up and stick to it!”

Now, imagine the straw is made of something super slippery, like it’s covered in soap or oil. The water touches it and goes, “Yuck! I don’t like this!” 😝

Instead of climbing up, the water stays down or even goes back down.
That’s reverse capillary action — it’s like the water is running away from the straw instead of climbing up.

Now let’s understand the working principle behind this, why this happens.

What is the normal capillary action first?

Capillary action happens when a liquid (like water) moves up in a thin tube or space against gravity. This happens because of two forces:

  1. Adhesion– the force between the liquid and the surface (e.g., water sticking to glass).
  2. Cohesion – the force between the molecules of the liquid (e.g., water sticking to water).

If adhesion > cohesion → the liquid climbs up the surface (capillary rise).

Working Principle of reverse capillary action

reverse capillary action

Surface properties matter:

  • If the surface is hydrophobic (water-hating), like wax or Teflon, water molecules don’t want to stick to it.

Adhesion is low:

  • Water tries to pull itself together (cohesion is high) but avoids the surface.

Gravity wins:

  • Without enough adhesion to pull the water up, gravity pulls it down.

Real-world example:

Think of how water rolls off a lotus leaf — that leaf is hydrophobic. If you made a tiny tube from a material like that, water wouldn’t climb up — it would stay down or slide back. That’s reverse capillary action in action.