Dynamic Aspects of Wetting Balance Tests

Abstract

The relationships between the force measured during wetting balance tests and the observed changes of contact angle and meniscus shape are studied. Experiments using silicone oil at 25, 50, and 100°C on glass plates as well as Pb-Sn eutectic solder on Au-coated glass plates are reported. Discrepancies between the measured force and height and those expected for a static meniscus are detailed. Equilibrium meniscus shapes are computed for wide plates using the elastica solution and for narrow plates using the public-domain software package, “Surface Evolver.” For room temperature experiments with oil, the measured force discrepancy disappears when the meniscus rise is complete. Thus, the force discrepancy may be due to shear stress exerted on the sample by fluid rising up the sample. For static menisci with heated liquids, force and meniscus height discrepancies do not disappear when the meniscus rise is complete. These discrepancies can be explained by Marangoni flow due to temperature gradients in the fluid for the oil experiments but not for the solder experiments.