Capillary action is the ability to flow against gravity. This can be seen when a liquid spontaneously rises in a thin tube like a straw. The next time you place a straw in your drink, compare the level of the liquid in the straw to the level of the liquid in the glass or bottle. The liquid level in the straw is generally higher. This is due in part to the attractive forces between the molecules of the liquid and the solid surrounding forces. If a tube is narrow enough, the combination of surface tension and forces of adhesion between the liquid and the walls of the tube is enough to lift the liquid.
This doesn’t just happen in straws or narrow tubes of glass. This can also happen in porous materials like paper and even in some non-porous materials like liquefied carbon fibre. Without capillary action, drainage of tear fluids from our eyes would be a much different experience as this fluid is constantly produced to keep our eyes lubricated. Smart materials or wicking fabrics used widely in athletic clothing utilise capillary action to draw sweat away from the skin. If you have ever wiped up a spill with a sponge, the pores in the sponge act as small capillaries to absorb the liquid.
Thin layer chromatography, an analytical chemistry technique depends upon capillary action. A solvent carrying dissolved solutes travel vertically across a plate. The solutes travel in the solvent at different rates depending on their attraction to the solvent or the coating of the plate.
Then of course, you could always use capillary action in a work of art.
- Hummingbirds Are Not Sipping Straws. They’re Doing Something Much Weirder. | 80beats (blogs.discovermagazine.com)
- Micro-origami unfolds in water (newscientist.com)