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Figure 10.8.
A Pendant drop deforming under gravity.
The fit has two main variables: droplet radius and B (a fitting constant).
Figure 10.9.
shows the affect that
both the fitting constant and the radius have on a simulated droplet. The B value changes how a droplet
shape deviates from a circle. The higher the value of B, the more deformed the droplet becomes due to
gravity. Droplets with low surface tension are more deformed by gravity, so increasing B will result in a
droplet fit with a lower surface tension.
Changing the radius does not alter shape of the droplet like changing B does, however it changes the scale of
the droplet. If a droplet volume is increased by increased its radius, it will deform more under the increased
gravity. If two droplets have the same shape but different sizes, the larger droplet must therefore have
a higher surface tension to retain the same shape with a higher volume. This means that increasing the
simulated droplet radius will increase the surface tension.
10.4 Pendant Drop Fitting
An optical tensiometer is a tool for measuring the surface tension of a liquid. The surface tension of a liquid
determines how it changes shape under gravity, and thus the shape of a droplet as it hangs off a needle
tip.
Figure 10.8.
shows a droplet attached to the end of a micropipette needle. The top of the droplet is
elongated, as the droplet deforms under its own weight. If we know the density and volume of the droplet,
then we can use its shape to determine its surface tension.
Summary of Contents for L2004A1
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