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 direction al converter arm, in vertical-pull surface force measurements. The Padday r od-pull technique, the du Nouy ring method, and the Wilhelmy plate method a re utilized with rods, thin-walled tubes, wire rings, and plates either rig idly 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-l oading 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 te nsion measurements, with samples having volumes of only a few tenths of a m illiliter. Measurements on very small liquid volumes are feasible because t he rod is firmly attached to the converter arm rather than hanging freely a s in measurements with balances mounted above the sample; therefore, the ro d cannot swing toward and attach to the wall of small sample tubes. Automat ion of force and height measurements with the converter arm/top-loading bal ance method is straightforward. (C) 1999 Academic Press.