30 Jan

Surface Tension

Surface tension can be measured using  tensiometers.  The units used to express surface tension are dyn/cm (dynes per centimeter) and are represented by the symbol \scriptstyle\gamma.  Surface tension is the result of the cohesive forces of molecules in a liquid; these forces pull a volume of  liquid to the smallest smoothest surface area possible.  A liquid will resist deformation of the smooth surface by an object in contact with the surface.  This makes it possible for objects which have higher density than the liquid to float on the surface of the liquid.  The classic example is the water strider.  Surface tension is also responsible for the beading of liquids on surfaces and the shape a drop of liquid takes.

The Du Noüy ring method for measuring surface tension uses a ring submerged into the sample.  The force required to pull the ring free from the surface tension of the sample is read as dyn/cm.  Surface tension is important in the ink, paint, and coatings industries as it affects the spreading ability of formulations.  Many additives such as wetting agents or surfactants affect the surface tension properties of liquids.  Measurement of surface tension can help predict the success of an ink or paint formulation.

Robin Prymula