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

Introduction 

What is ASTM C813?

ASTM C813 works by determining the contact angle between the glass surface and the particle of hydrophobic contamination. Hydrophobic contaminants are organic molecules attached to the surface of glass. ASTM C813 identifies the layers of the organic molecules by evaluating the contact angle. Organic molecules cause the contact angle of glass to vary. Contact angle is a situation where a liquid or vapor interface meets the solid surface. It measures the ability of a fluid to wet a solid surface through the use of Young’s equation. Hydrophobic contaminants can impact glass performance in various uses such as windows, displays, or optical applications.

Difference between ASTM C813 and ASTM C813-20

ASTM C813 serves as the basis for standardizing a method for detecting hydrophobic contamination on glass using contact-angle measurements. The updated ASTM C813-20, amended in 2024, may subtly enhance it with minor clarifications and updated best practices to align with the international standards for improved precision and safety measures.​

Scope of ASTM C813

This test method helps to measure hydrophobic contamination of the glass surface. The measurement is done by determining the contact angle that will be formed between the liquid used, usually water, and the glass surface to judge the level of contamination. There may be a need to test whether the glass surfaces are clean and suitable for particular applications where cleanliness and hydrophobic characteristics will be called up.

Significance of ASTM C813

The contact angle test is non-destructive and can be applied. The various processes of removing pollutants from the environment are controlled and assessed—hydrophobic contaminants. Testing can also be done to detect and manage hydrophobic contaminants in processing ambients. For this purpose, a surface free from hydrophobic films is exposed to ambient conditions and then tested.

ASTM C813 Test Procedure

The test equipment used in ASTM C813 are as follows 

ASTM C813 Test method 

1. Clean glass surface free of obvious contamination. This may be accomplished with solvents or detergents followed by washing and drying. 
2. Condition the glass at ambient for some specific period if relevant. 
3. Use a microsyringe or automated dispenser to deposit a small, accurate volume of test liquid, often deionized water, onto the surface of the glass.
4.  To ensure accuracy, the contact angle between the liquid droplet and the glass substrate should be measured using a contact angle goniometer at different locations. 
5. Record the readings of the contact angle values and note droplet shape or behavior observations. 

Specimen Size

The contact angle measured on the glass surface is reported. As per the standard, Common sizes of the glass specimen are around 1 cm² to 5 cm², but the surface is free of hydrophobic contaminants if the advancing angle is not greater than 5°. 

Result Analysis 

The results are provided as the contact angle between the liquid droplet and the surface of the glass. A higher contact angle implies that the surface is more hydrophobic, while a low contact angle would imply that the surface is too wettable or contaminated. These results are given in degrees.

Conclusion

The contact angle measurements made in the ASTM C813 hydrophobic contamination of the glass test are within acceptable limits for the intended use and hydrophobically sufficient, indicating excellent cleanliness and no significant contamination. The contact angles were neither deviated nor irregular, so the glass satisfied the requirements as indicated in hydrophobic performance. Further actions that comprise regular monitoring may be suggested to ensure that the surface’s quality remains good.

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