A more general approach to understanding a surface’s wettability is through surface free energy analysis. By measuring the contact angle formed by probe liquids with known surface tensions values, the surface free energy components are calculated using analysis models. Popular analysis models are acid-base, Kitazaki-Hata, Owens-Wendt, Kaelble-Uy, and Wu for expressing the work of adhesion term of the Young-Dupré theory. Additionally, knowing the contact angle and surface tension of the probe liquids leads to the critical surface tension using a Zisman Plot.

Typical Experimental Results:

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Contact angle measurement of water (left) and diiodomethane (right) for surface free energy analysis of a metal plate

 

Surface Free Energy of Two Gelatin Samples

Theory of Energy Analysis Kaelble-Uy Wu Owens-Wendt
Specimen CA. (deg) S.F.E. (mJ/m2) S.F.E. (mJ/m2) S.F.E. (mJ/m2)
Water Methylene Iodide d p Total d p Total d h Total
Gelatin 1 87.5 57.5 26.9 3.7 30.6 24.5 8.6 33.1 27.5 3.6 31.1
Gelatin 2 73.3 59.5 22.5 12.0 34.5 21.3 16.7 38.0 24.0 11.3 35.3

d = dispersive component, p = polar component, h = hydrogen-bond component

 

Applications:

Acid-Base Contact Angle from Probe Liquids Dispersive Components
Gelatin Hydrogen-Bond Interfacial Free Energy
Kaelble-Uy Kitazaki-Hata Lifshitz-Van der Waals Components
Liquid/Liquid Interaction Owens-Wendt Polar Components
Rubber Solid/Liquid Interaction Solid/Solid Interaction
Surfactant Performance Thin Films and Coatings Work of Adhesion
Wu Young-Dupre Zisman Plot

For more information please read our application notes:
Surface Free Energy Analysis of Gelatin Samples

 

Key Specifications:

Resolution 0.1°
Measure Range 0-180°
Image Capture Device CCD Camera at 60 FPS
Analysis Method Half angle, circle, ellipse, tangent
Maximum Sample Size 150x150x35mm
Maximum Sample Weight 400g
Instrument Rotation 90°
Stage Rotation 360°

 

Instruments: The DM-701 Fully Automatic Contact Angle Meter

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Surface Free Energy Analysis of Gelatin Samples

 

Contact angle measurement can provide useful information about the wetting characteristics of a surface and a liquid. Further, by using different probe liquids with known polar, non-polar, hydrogen-bond energy components, the surface free energy of a solid surface can be determined through contact angle measurement. Surface free energy is the excessive energy existing on the surface of a solid due to imbalanced intermolecular forces among molecules of the solid. The surface free energy provides a more general characterization of a surface chemically and energetically and its analysis is of significance to numerous applications such as wetting, cleaning, contamination, adhesion, friction, lubrication, and wear. For instance, with measured surface free energy values for any pair of solids or solid and liquid the work of adhesion between the two can be analyzed through the Young-Dupré theory.

 

AppNote-53

 

Table 1 presents the surface free energy analysis performed on two gelatin samples using the Kyowa contact angle meters equipped in our lab. Kyowa Interface Science’s contact angle measurement analysis software, FAMAS, supports five popular surface free energy analysis models. These models include Fowkes’ acid-base, Kitazaki-Hata, Owens-Wendt, Kaelble-Uy, and Wu Model. Each of the five models determines the same or different components that comprise the total surface free energy. As shown in Table 1, the Kaelble-Uy, Wu and OwensWendt models determine the values for each of the components. Because each model has its own assumptions and limitations there is not one that can be universally applicable to all surfaces and probe liquids. Sometimes a particular model will yield useful data and other times it will not based on the combination of solids and probe liquids chosen. In spite of that scientists and engineers may need to work with more than one model, surface energy analysis through contact angle measurement remains a favorite and popular choice for its component level analysis capability and easy of operation.

 

ASTM Number Title Website Link
D7490-13 Standard Test Method for Measurement of the Surface Tension of Solid Coatings, Substrates and Pigments using Contact Angle Measurements Link
D7541-11 Standard Practice for Estimating Critical Surface Tensions Link