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1.1 These test methods cover the determination of surface tension and interfacial tension of a variety of liquid materials, including but not restricted to paints, solvents, and solutions of surface-active agents, as defined in Terminology D459. Four methods are covered as follows:

Method A—Surface Tension by du Noüy ring.

Method B—Interfacial Tension by du Noüy ring.

Method C—Surface Tension by Wilhelmy plate.

Method D—Interfacial Tension by Wilhelmy plate.

1.2 Method A originally was written primarily to cover aqueous solutions of surface-active agents, but is also applicable to aqueous paints, nonaqueous solutions (including paints) and mixed solvent solutions.

1.3 Method B is applicable to two-phase solutions. More than one solute component may be present, including solute components that are not in themselves surface-active.

1.4 Method C is applicable to surface active liquids and, unlike du Noüy ring, no buoyancy corrections are needed and results are not affected by moderate viscosities (1-10 Pa-sec) of the liquid. It is the recommended method for use with paints and resin solutions.

1.5 Method D is applicable to two-phase solutions and mixtures.

1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Material Safety Data Sheets are available for reagents and materials. Review them for hazards prior to usage.

5.1 These methods provide data that are useful in evaluating the effectiveness of surface active agents in reducing surface tension. In addition, surface tension data can predict interactions between liquids and solid surfaces or other liquids and can be used to establish wetting properties of paints, solvents, and other liquids.

5.2 A number of laboratories have found the Wilhelmy plate to be easier to use, easier to clean and generally better for use with pigmented paints.