Measure Surface Tension?
Ray LaRue
I am an electronic engineer, not a chemist. But I need to find a
reliable way to measure surface tension changes from about 2 to 15 %. Is
there an economical way to do this in a small lab setting? Thank you for
your attention.
Gerry Elphingstone
Ray LaRue <rayl...@gte.net> wrote:
A surface tensionometer is fairly cheap and easy to operate. The one I
am thinking of uses a DuNouy ring. The ring itself may be expesive,
~$500.
Gerry
"Only two things are infinite, the universe and human
stupidity, and I'm not sure about the former."
-- Albert Einstein
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R. Daniel Davies
In article <32E94E...@gte.net>, Ray LaRue <rayl...@gte.net> writes
>I am an electronic engineer, not a chemist. But I need to find a
>reliable way to measure surface tension changes from about 2 to 15 %. Is
>there an economical way to do this in a small lab setting? Thank you for
>your attention.
I beleieve there is a simple method of using contact angle of a droplet?
sorry can't be of more help.
Daniel Davies
Thomas F. Pedersen
There are two simple ways to measure the surface tension.
The first invovlves measuring the contact angle of droplets of liquids
with different known surface tensions and then plotting cosine of the
contact angle vs. the surface tension of the liquid. Where this line
(it should be a line) crosses cosine = 1 the critical surface tension
of the surface is found.
The other also involves liquids of known surface tension. You apply the
liquid with a thin brush to the surface in a line. If the line breaks
up in droplets within 2 seconds after the application, the liquid "does
not wet the surface". Trying this with a range of liquids the surface
tension that just wets the surface can be found. This is called the
critical wetting tension. It is also described in an ASTM standard, but
I can't remember the number just now.
Sincerely Yours
Thomas Fich Pedersen
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Thomas Fich Pedersen
Falstersgade 10, 2
DK-7000 Fredericia
+45 75 93 15 15
Thomas F. Pedersen
Gerry Elphingstone
Thomas_F....@online.pol.dk (Thomas F. Pedersen) wrote:
>There are two simple ways to measure the surface tension.
>
>The first invovlves measuring the contact angle of droplets of liquids
>with different known surface tensions and then plotting cosine of the
>contact angle vs. the surface tension of the liquid. Where this line
>(it should be a line) crosses cosine = 1 the critical surface tension
>of the surface is found.
>
This method only works if the fluid is nonpolar. This is known as the
Fox-Zisman method. There is a good review paper discussing the
invalidity of this method by R. J. Good, "Contact Angle, wetting, and
adhesion: a critical review." J. Adhesion Sci. Technol., Vol. 6, No.
12, pp. 1269-1302 (1992).
>The other also involves liquids of known surface tension. You apply the
>liquid with a thin brush to the surface in a line. If the line breaks
>up in droplets within 2 seconds after the application, the liquid "does
>not wet the surface". Trying this with a range of liquids the surface
>tension that just wets the surface can be found. This is called the
>critical wetting tension. It is also described in an ASTM standard, but
>I can't remember the number just now.
>
>Sincerely Yours
>Thomas Fich Pedersen
I have never heard of this method, but it could only be empirical.
There are much better methods out there now. The cheapest way to
measure the surface tension is the DuNouy ring or something similar. I
believe the most accurate seems to be the pendant drop method.
Contact angle methods such as direct measurement from a sessile drop
or the Wilhelmy plate method are usefull to measure the surface free
energy. A number of good discussions of various experimental methods
may be found in "Surface and Colloid Science", Vol. 11, ed. Robert J.
Good and Robert R. Stromberg (1979).
Jeffrey Krueger
For the accuracy you require I would consider using a wilhelmy plate/rod
technique. Essentially, you measure the force of the liquid on a platinum
rod or plate of known perimeter. Subtracting off the bouyant force (by
adjusting the rod so it just contacts the liquid) the force is equal to
the liquid surface tension times the perimeter times the cosine of the
contact angle: F=sPcosA.
Another method to cosider is the DeNouy Ring technique. In this method you
measure the force required to pull a ring out of the liquid. The calculation
is based upon the specific geometry of the ring. An apparatus cost about $600
from VWR.
I like the Wilhelmy technique because all you need is a microbalance and
a micropositioner. Remember that a force on the rod produces an
opposite force on the liquid. This makes things easier to set up (no hang
down wire necessary)
Jeffrey Krueger
Columbia, SC
John B McQuillen
In article <32E94E...@gte.net>, rayl...@gte.net says...
>
>I am an electronic engineer, not a chemist. But I need to find a
>reliable way to measure surface tension changes from about 2 to 15 %.
Is
>there an economical way to do this in a small lab setting? Thank you
for
>your attention.
For about 5% accuracy in non-water systems, the "cheapest" method is the
capillary rise method whereby a transparent capillary tube is partially
submerged into a beaker containing the test fluid. The liquid rise
within the capillary is related to the surface tension of the fluid by
the following:
h = 2*[surface tension]*cosine[contact angle]/([liquid
density]*[acceleration due to gravity]*[internal radius of capillary
tube].
Multiple measurements are usually performed with several capillary tubes
of different diameters.
For a reference on measuring surface tension (this was is actually for
measuring interfacial tension between two immiscible fluids - a good
starting point) see
N. Rashidnia, R. Balasubramanium, D. Del Signore "Interfacial Tension
Measurement of Immiscible Liquids using a Capillary Tube," AIChE
Journal, April 1992, Vol. 38, No. 4, pp 615-618.