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2013 Clark Scholar Demonstration

Hysteresis in the contact angle at the interface between a solid and a liquid is a phenomenon that enables the retention of liquid in a narrow tube. Without this effect, soil would not have the ability to retain moisture. Therefore, contact angle hysteresis is a fundamental phenomenon without which agriculture is impossible.

Clark Scholar Larry Zhang conducted experiments to study contact angle hysteresis during Summer 2013. Drops of water were added to a slide which was pre-treated with the non-polar solvent heptane. These drops were imaged using a dissection microscope and a digital camera. The video shows the sequence of images obtained from both cameras. The images were analyzed by Larry using MatLab and the contact angle was plotted against the diameter of the contact region. The accompanying figure shows the result of the experiment.