ASTM D7334 outlines the standard practice for surface wettability of coatings, substrates and pigments using the measurement of advancing contact angle. The advancing contact angle describes the contact angle of a drop that is in motion. For the measurement, a goniometer is needed.
ASTM D7334: Application and Use
The contact angle is a parameter used to analyze the wetting behavior of a liquid on a solid surface. The static contact angle describes the state in equilibrium, i.e., at rest. Dynamic contact angles describe a drop of liquid that is in motion. A distinction is made between advancing contact angles, which describe how a liquid drop wets a solid, and receding contact angles, which characterize how the liquid detaches from a wet solid surface area. The standard ASTM D7334 describes how to measure the advancing contact angle.
A surface that wets easily often shows better adhesion and appearance when a coating is applied. When using water as a test liquid, the sample surface can be classified as either hydrophilic, when the angle is smaller than 45°, of hydrophobic, when the contact angle is greater than 90°
ASTM D7334: Experimentation
Apparatus
The apparatus for this standard should include:
- a stage with a flat surface
- a device, like a syringe, to place a drop on the surface
- a light source
- a microscope or camera
- a software to determine the contact angle
All Contact Angle Meters, or Goniometers, of the OCA series from DataPhysics Instruments comply with this standard.
Procedure
he experiment is conducted as follows:
- Place the sample surface on the stage and fix it
- Deposit a drop of liquid on the surface
- Measure the contact angle
The ASTM D7334 is in use since 2008 and was last re-approved in 2022.
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