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Density and Surface Tension
Name: Heather
Status: student
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Question:
Does the density of a liquid affect its surface tension?
Replies:
The quick answer is that no, density and surface tension are not tightly
related. You can find examples of all four combinations dense-high-tension,
dense-low-tension, low-density-high-tension, and low-density-low-tension.
That is not to say there is no relationship though. This question can get
very complicated very quickly, so I will try to be brief -- the nature of the
molecules involved and how attractive they are to each other or to other
molecules (such as on a surface) affect both density and surface energy.
Molecules that are strongly attracted to each other tend to have higher
surface tension and higher density. However, since molecules can be very
different -- small molecules like water, intermediate molecules like organic
alcohols, and large molecules like polymers -- and one place on a molecule
can be chemically different than another place, many possibilities exist.
Hope this helps,
Burr Zimmerman
It all depends upon the geometry of the liquid setup -- bubbles, foams, flat
surface -- the relation between surface tension and density is different for
each case. A common arrangement is the rise of a column of liquid in a uniform
capillary of radius 'r'. In this case, the liquid will rise in the capillary a
height 'h' which is given by: 1/2 x (h x d x g x r) = S. Here, 'd' is the
density of the liquid, 'g' is the gravitational constant, and 'S' is the surface
tension. This capillary rise is used to measure the surface tension of liquids.
A word of caution, however. Because surface tension is a "surface phenomenon" it
is subject to minute changes in the liquid, the surface in contact, and other
experimental variables -- it is not an easy property to measure accurately.
Vince Calder
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Update: June 2012
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