When using the Wilhelmy method for contact angle measurements, the thickness and the width of the sample need to be known as the wetted length is directly proportional to the force measured during the experiment. In many cases, this is not a problem as dimensions are easily measured. However, in the case of a fiber, the diameter of the fiber is not necessarily known and due to its small size, the measurement can be tricky. In this blog post, the importance of the fiber diameter is discussed, and different measurement methods are proposed.
In the figure below, we explore how errors in fiber diameter (0.5 % to 3 %) can affect the accuracy of contact angle measurements at various contact angles. The data shows that when contact angles are at extreme values—either very low or very high—the results are particularly sensitive to inaccuracies in fiber diameter. In case the absolute contact angle values need to be known, the accurate determination of the fiber diameter is thus critical.
However, one should note that if the purpose of the contact angle measurement is to compare different fibers with the same nominal diameter to each other, this can be done even without exact dimensions. The order of the samples in terms of wettability can be determined even if the absolute contact angle values are not correct.
In case the absolute diameter needs to be known, there are several ways to measure it:
Microscopy Techniques: These are the most accurate methods for measuring fiber diameter. However, they require access to a microscope, which may not always be available.
Using a Force Tensiometer: If a microscope is not available, a force tensiometer can be used to determine fiber diameter. This method involves measuring the fiber against a liquid with a contact angle of zero.
Here’s how it works:
To learn more about how to measure the wettability of fibers and how the fiber diameter can be determined, please watch the webinar through the link below.
Susanna is an Application Scientist at Biolin Scientific. In her PhD thesis, she developed fabrication methods for a new type of inorganic-organic polymers. Microfabricated polymer chips were utilized as tool for biomolecule separation in analytical chemistry.
