Definition - What does Capillarity mean?

Capillarity is the depression or the rise of a liquid in a small capillary passage tube having small cross sectional area such as openings in the porous materials. Capillary action of a fluid can be experienced in both vertical and horizontal directions. In the capillarity or capillary action, the fluid moves in an upward direction against the force of gravity. It is also known as capillary action.

Petropedia explains Capillarity

Capillarity occurs because of intermolecular forces between the liquid and surrounding solid surfaces. It is caused by the pressure of cohesion and adhesion, which causes the liquid to work against gravity.

The effect of capillary action can be seen in:

  • Drawing up of liquids between the hairs of a paintbrush
  • Thin tubes
  • Porous materials such as paper
  • Some non-porous materials, such as liquefied carbon fiber
  • Cells

Capillary action has many significant applications like thin layer chromatography, in which a solvent moves vertically up a plate via capillary action. The small pores of a sponge act as small capillaries, causing it to absorb a large amount of fluid. Some textile fabrics are said to use capillary action to "wick" sweat away from the skin. These are often referred to as wicking fabrics, due to the capillary properties of candle and lamp wicks. In brazing, capillary action causes a filler metal to be drawn into the space between work pieces.

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