Surface tension of liquid marbles, an experimental approach

The capillary rise technique has been used to experimentally study the “surface tension ” of liquid marbles formed by encapsulating water droplets with polytetrafluoroethylene (PTFE) powder of 1, 35, and 100 µm particle size. In a typical experiment, a glass capillary tube was inserted into a water marble to measure the capillary rise of the water. The Laplace pressure exerted by the water marble was directly measured by comparing the capillary rise data from the marble and from a flat water surface in a beaker. An equation to calculate the water marble surface tension based on the Murmar’s model is then proposed. It is also justified how the capillary rise measurements the liquid marble surface tension does not require the water contact angle with any solid surface to be considered; which therefore makes a simple but efficient method for determining liquid marble surface tension. A discussion on the nature and the realistic magnitude of liquid marble surface tension is offered.