Capillary Action: How Blotting Paper Absorbs Ink

Subject :Science and technology

Section: Msc

Capillary Action Explained:

Capillary action is a natural phenomenon displayed by liquids aiming to reduce surface tension.
Liquids in thin tubes with very fine bores, known as capillary tubes, exhibit this action.
When immersed in a liquid, the liquid rises higher inside the capillary tube than outside, driven by capillary forces.
Liquids with contact angles less than 90 degrees exhibit capillary action, causing them to rise; those like mercury do not.
Adhesive Forces: The liquid molecules are attracted to the surface of the cellulose fibers in the blotting paper. This attraction is due to intermolecular forces, such as hydrogen bonding or van der Waals forces.
Cohesive Forces: The liquid molecules also exhibit cohesive forces, meaning they are attracted to each other and tend to stick together.

Blotting Paper Composition:

Blotting paper is composed of cellulose derived from cotton linter, wood, or straw.
It’s created by directly pressing purified pulp paste, forming sheets with microscopic capillaries.

Absorption Mechanism:

When blotting paper comes into contact with ink, water, or aqueous solutions:
- The liquid enters the microscopic capillaries in the paper.
- Capillary action allows the solution to spread throughout the paper.

Everyday Applications:

Capillary action is responsible for several common phenomena:
- Plant Sap Movement: Helps plants transport sap from roots to the top via the stem.
- Wickstove Function: Draws kerosene or oil up to the wick tip in lamps, where it’s burned.