Directional Converter Arm Method for Surface and Interfacial Tension Measurements with a Top-Loading Balance

A method is described for utilizing a top-loading balance, with a directional converter arm, in vertical-pull surface force measurements. The Padday rod-pull technique, the du Noüy ring method, and the Wilhelmy plate method are utilized with rods, thin-walled tubes, wire rings, and plates either rigidly attached to the converter arm or hanging freely from a hook at the end of the arm. The robustness, large weighing capacity, and accuracy of top-loading balances make them ideally suited for a variety of types of surface and interfacial tension measurements. The converter arm method can be used with a stainless steel rod (3–7 mm in diameter) in vertical-pull surface tension measurements, with samples having volumes of only a few tenths of a milliliter. Measurements on very small liquid volumes are feasible because the rod is firmly attached to the converter arm rather than hanging freely as in measurements with balances mounted above the sample; therefore, the rod cannot swing toward and attach to the wall of small sample tubes. Automation of force and height measurements with the converter arm/top-loading balance method is straightforward.