Liquids Du Nouy Ring and Wilhelmy Plate Methods

The du Nouy ring and Wiiheimy plate methods (Fig. 3.4) are two most frequently used techniques of measuring surface tension at the liquid—air interface or mterfacial tension at a liquid—liquid interface. Only the du Nouy method can be applied to measure interfacial tension. Both of these techniques are based on pulling an object with a well-defined geometry off the surface of liquids and measuring the pull force. These techniques are also known as pull-force methods. In the Wiiheimy method, a plate is the pull object, whereas in the du Nouy technique a ring is used. These techniques are ascribed to two scientists who conducted some of the earliest research in the area of surface tension measurement. In 1863, Wilhelmy described measurement of capillary constants in a paper, without a detailed calculation of surface tension. Lecomte du Nouy illustrated the 

Wiiheimy Piate This technique is broadiy appiicabie to iiquids, especiaiiy when surface tension must be measured over a iong time period. A verticai piate with known perimeter is attached to a baiance and submerged in the iiquid. The force due to wetting is measured by the baiance. 

Spinning Drop Suitabie for iow interfaciai tensions. The diameter of a drop within a heavy phase is measured when both are being rotated. 

Pendent Drop Surface and interfaciai tensions are measured by this method. 

Bubble Pressure This method is used for determining surface tension at short surface ages. The actuai measured variabie is the maximum pressure of each bubbie. 

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Measurement for Liquids du Nouy Ring and Wilhelmy Plate Methods... 

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