In paper chromatography, solvent moves up paper via capillary action, moving pigment molecules with it |
Capillary Action
Definition and Examples
A spontaneous flow of liquid that doesn't require gravity to
work
By Anne Marie Helmenstine, Ph.D.
Capillary action is defined as the spontaneous flow of a liquid into a narrow tube or porous
material.
This movement does not require the force of gravity to occur. In
fact, it often acts in opposition to gravity.
Capillary action is sometimes called capillary motion,
capillarity, or wicking.
Capillary action is caused by the combination of cohesive forces of the liquid and the
adhesive forces between the liquid and tube material.
Cohesion and adhesion are two types of intermolecular forces.
These forces pull the liquid into the tube. In order for wicking
to occur, a tube needs to be sufficiently small in diameter.
Examples of capillary action include the uptake of water in
paper and plaster (two porous materials), the wicking of paint between the
hairs of a paintbrush, and the movement of water through sand.
Fast Facts: History of Capillary Action Study
· Capillary action was first recorded by Leonardo da Vinci.
· Robert Boyle performed experiments on capillary action in 1660,
noting a partial vacuum had no effect on the height a liquid could obtain via
wicking.
· A mathematical model of the phenomenon was presented by Thomas
Young and Pierre-Simon Laplace in 1805.
· Albert Einstein's first scientific paper in
1900 was written on the subject of capillarity.
See Capillary Action Yourself
An excellent and easy demonstration of capillary action is done
by placing a celery stalk in water.
Color the water with food coloring and observe the progress of
the dye up the celery stalk.
The same process may be used to color white carnations.
Trim the bottom of a carnation stem to make sure it can absorb
water. Place the flower in dyed water.
The color will migrate via capillary action all the way to the
flower petals.
A less dramatic but more familiar example of capillary action is
the wicking behavior of a paper towel used to wipe up a spill.
Anne
Marie Helmenstine, Ph.D.
Chemistry
Expert
Education
Ph.D.,
Biomedical Sciences, University of Tennessee at Knoxville
B.A.,
Physics and Mathematics, Hastings College
Introduction
Ph.D.
in biomedical sciences from the University of Tennessee at Knoxville - Oak
Ridge National Laboratory.
Science
educator with experience teaching chemistry, biology, astronomy, and
physics at the high school, college, and graduate levels.
ThoughtCo
and About Education chemistry expert since 2001.
Widely-published
graphic artist, responsible for printable periodic tables and other
illustrations used in science.
Experience
Anne
Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education
since 2001, and other sciences since 2013. She taught chemistry, biology,
astronomy, and physics at the high school, college, and graduate levels.
She has worked as a research scientist and also abstracting and indexing
diverse scientific literature for the Department of Energy.
In
addition to her work as a science writer, Dr. Helmenstine currently serves as a
scientific consultant, specializing in problems requiring an interdisciplinary
approach. Previously, she worked as a research scientist and college
professor.
Education
Dr.
Helmenstine holds a Ph.D. in biomedical sciences from the University of
Tennessee at Knoxville and a B.A. in physics and mathematics with a minor
in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine
developed ultra-sensitive chemical detection and medical diagnostic tests.
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