Contact Angle

       A necessary condition for the formation of a proper fiber-resin interface is that the liquid resin "wet" or spread on the fiber surface.  Contact angle measurements can be performed to analyze the compatibility between the fiber and matrix.  The contact angle is a measurement taken as a drop of liquid forms on the solid fiber.  If the contact angle is less than 90o then the liquid is thought to wet the solid and in an extreme case, when the angle is 0, the liquid is said to spread on the surface.  Both wetting and spreading give acceptable interfacial free energy for adhesion in that the thermodynamic work of adhesion is positive.  Below is a list of advantages and disadvantages for the contact angle technique.
 

Advantages
Disadvantages
1.  Inexpensive
2.  Rapid
3.  Provides information related to surface energetics
4.  Hydrated samples can be observed		 1.  Artifact-prone: swelling of substrate, leaching and
     extraction, penetration, surface reorientation, roughness,
     operator bias
2.  Liquid purity is of critical importance
3.  Only surface energetics information is obtained
4.  Surface chemistry information is ambiguous

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