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Comparatively Speaking: Static vs. Dynamic Measurement of Surface Tension
By: Anthony J. O'Lenick, Jr., Siltech LLC
Posted: December 2, 2009
page 2 of 2
Each of these methods also comes in "flavors." One "flavor" is a static measurement in which the liquid is not moving. The other "flavor" is a dynamic measurement in which the liquid is moving. Often the static and dynamic surface tension have different values that are real and not just experimental error. The difference between the static and dynamic value can be very useful in understanding the surface properties of the liquid.
In relation to formulas, the static surface tension would be the surface tension in a bottle; an interesting determination, but perhaps not the most important one. As the product is poured from the bottle and used, dynamic surface tension becomes more important since the formulation is spread onto the hair or skin, creating a new surface area. This increase in surface area occurring during application results in a dynamic situation, where surfactant present in micelles transfers to the newly created surface to lower surface tension. Figure 1 illustrates the different forces in play during the complex situation of applying the formulation.