Test for Hydrophobic Contamination on Glass by Contact Angle Measurement ASTM C813

Test for Hydrophobic Contamination on Glass by Contact Angle Measurement ASTM C813

ASTM C813 detects hydrophobic contamination on glass surfaces by measuring the contact angle. Hydrophobic contaminants are organic molecules sticking on the glass surface. The test is used to detect hydrophobic contaminants on glass that harbors when exposed to ambient end use conditions. Values are expressed in SI units.


    ASTM C813 detects layers of organic molecules by observing contact angle measurements. Organic molecules change the contact angle of glass. The contact angle is the angle where a liquid-vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation. 

    The data from the contact angle test is used to evaluate processes that remove hydrophobic contaminants. It is used to detect glass that harbors hydrophobic contaminants when exposed to ambient conditions. For this, a surface free of organic films is exposed to the ambient conditions and is later tested.

    Test Procedure:

    Drops of permanganate-distilled water are deposited on the glass surface using a mounted hypodermic syringe to measure the advancing contact angle. The contact angle is measured by either (1) viewing a sessile drop through a comparator microscope with a goniometer scale; or (2) photographing a sessile drop and measuring the angle with a protractor.

    Organic contamination on surfaces leads to contact angles higher than the near-zero angles on clean surfaces. The sensitivity of this test decreases if the surface is rough or porous, or if the surface has hydrophilic substances.


    The contact angle measured on the glass surface is reported. The surface is free of hydrophobic contaminants if the advancing angle is no greater than 5°. 


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