Fiber wettability is important in many different applications such as material development. In material development, fibers are used to produce fiber-reinforced plastics for lightweight and durable material properties. Fiber wettability is crucial in these materials because it significantly influences the adhesion between the fibers and the matrix, which in turn affects the mechanical properties of the composite. Proper wettability ensures that the resin thoroughly wets the fibers, leading to improved load transfer and enhanced mechanical performance. Incomplete wetting can result in interfacial defects, reducing adhesion and potentially compromising the structural integrity of the composite. Additionally, understanding and optimizing fiber wettability is essential for various industrial processes, such as dyeing, coating, and adhesion, which can improve product performance, durability, and efficiency.
Single fiber contact angle
While there are several methods available for single fiber contact angle measurements, the Wilhelmy plate method offers several advantages over the other techniques. Probably the most clear reason to use the Wilhelmy plate measurement is the ability to measure fibers down to 7 μm in diameter which is the typical diameter of the carbon fiber. However, several things should be considered especially when single fibers are measured.
- Sensitive measurement requires a proper measurement environment
As single fibers are measured, the measured forces are extremely small which puts a lot of requirements to the measurement environment. The instrument must be placed in a vibration-free area, on a steady or active anti-vibration table. In addition, the instrument needs to be protected from the airflow (such as air conditioning) as any additional movement in the probe will be detected by the balance.
- Surface tension of the liquid
In the contact angle calculations, the surface tension of the liquid is needed. It’s common practice to use literature values for surface tension of the liquid but care must be taken to ensure that there is no contamination in the liquid or measurement cup. If there is a risk of contamination, the surface tension of the liquid can easily be measured with the same instrument using the Du Nouy ring or the Wilhelmy plate method.
- The diameter of the fiber
In Wilhelmy plate measurement the wetted length is needed to calculate the contact angle. This is the perimeter of the sample and thus fiber diameter has to be known. Fiber diameter is typically measured with a microscope, preferably scanning electron microscope if the fiber diameter is small. Although incorrect fiber diameter will lead to errors in contact angle determination, one should note that comparing the contact angles between fibers is still correct. For example, suppose carbon fibers have the same nominal diameter but different surface treatments. In that case, the contact angle results will indicate which samples are more easily wetted even if the absolute contact angle is not exactly correct.
To learn more about contact angle measurement techniques for fibers, please register for the webinar below.
