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ramé-hart Newsletter


February 2024

Ten challenges when measuring contact angle on polymers and how to address them

Measuring contact angles on polymer solids can present various challenges due to the unique properties and characteristics of polymers. Here's a list of challenges associated with measuring contact angles on polymers and solutions for overcoming them:

1. Surface Heterogeneity: Polymers often have complex and heterogeneous surfaces, with different functional groups and textures. This heterogeneity can result in variations in contact angles across the surface. By taking a large number of sample readings, you can find the mean which gives a good glimpse at the average wetting properties of the surface. However, you should also report the standard deviation when reporting the results.

2. Chemical Composition: The chemical composition of polymers can vary, leading to different interactions with the testing liquid. Some polymers may be more polar or hydrophobic, affecting wetting behavior. Testing in a variety of different locations can help you better understand if the chemical composition is consistent across the sample or from one sample to another.

3. Surface Contamination: Polymer surfaces are prone to contamination from environmental factors, handling, or processing. Contaminants can alter the surface properties and affect contact angle measurements. Ensure that the samples are clean and blow off any dust prior to collecting contact angle measurements.

4. Surface Roughness: Polymers may have microscale or nanoscale roughness that can impact contact angle measurements. High roughness can lead to difficulties in defining a clear contact line. Consider measuring not only the equilibrium contact angle but also the advancing and receding contact angle and roll-off angle. As roughness increases, so too does the roll-off angle and pinning behavior.

5. Absorption of Testing Liquids: Some polymers are porous or absorbent, leading to the penetration of testing liquids into the material. This can affect the measured contact angle and the interpretation of wetting behavior. In some cases, you may wish to use a captive bubble technique which is an ideal method for measuring wetting properties on a porous solid.

6. Dynamic Surface Changes: Polymers can exhibit dynamic surface changes over time, especially in response to environmental conditions (e.g., humidity, temperature). This dynamic behavior poses challenges in obtaining consistent and reproducible contact angle measurements. Use an environmental chamber or cell to control the temperature and humidity during contact angle measurements to eliminate environmental variables. 

7. Surface Energy Hysteresis: Polymers may show hysteresis in contact angle measurements, meaning that the advancing and receding contact angles are different. This can complicate the interpretation of wetting behavior. Report both the equilibrium contact angle as well as the contact angle hysteresis.

8. Polymer Aging: Over time, polymers can undergo changes in their properties due to factors such as oxidation, UV exposure, or thermal degradation. Aging can influence the surface characteristics and, consequently, contact angle measurements. By measuring the change in contact angle over time (in some cases, days and weeks), you can determine the affects of aging on wetting properties.

9. Limited Availability of Standard Methods: Unlike metals or glass, there may be a lack of standardized methods for measuring contact angles on polymer surfaces. Choosing appropriate methods and protocols is crucial for reliable and comparable results. Always use a standard protocol or method and then be consistent. When comparing results, ensure the data are from studies using the same methodology.

10. Influence of Substrate: The substrate on which the polymer is deposited or coated can impact contact angle measurements. The interaction between the polymer and the substrate needs to be considered for accurate assessments. Always choose a substrate that is flat, smooth, chemically compatible, and has a similar surface energy. It should also be inert, non-absorbent and stable at any testing temperatures. Glass (e.g., glass slides) is frequently used for this purpose.

Addressing these challenges often involves careful sample preparation, selection of appropriate testing liquids, consideration of environmental conditions, and the use of advanced techniques for characterizing polymer surfaces. Researchers and scientists working with polymer materials must be aware of these challenges and solutions to obtain meaningful and accurate contact angle measurements.

Why are researchers interested in the water contact angle on polymer samples?

Knowing the water contact angle on a particular polymer sample is important to researchers for several reasons, as it provides valuable information about the surface properties and wetting behavior of the material. The water contact angle is a measure of the wetting or repellent characteristics of a surface, and this information is crucial in various scientific, industrial, and research applications:

1. Wettability and Adhesion: The water contact angle helps characterize the wettability of a polymer surface. A high contact angle indicates low wettability, suggesting that the surface repels water. Conversely, a low contact angle suggests high wettability. This information is critical in understanding how liquids interact with the polymer and is important in applications where adhesion or repellency is a key factor.

Screenshot of a water contact angle measurement on a polymer substrate

2. Surface Energy: The water contact angle is linked to the surface energy of the polymer. In fact, contact angle is measured first in ramé-hart DROPimage software and then the resulting data are analyzed using any one of a number of surface energy tools. Understanding surface energy is crucial in processes like adhesion, coating, and bonding. Materials with different surface energies may require different surface treatments or modifications for optimal performance in specific applications.

3. Biomedical Applications: In medical and biological applications, the water contact angle is important for understanding the biocompatibility of polymer surfaces. It influences how biological fluids interact with medical devices, implants, and other biomedical materials. A highly hydrophobic surface may reduce biofouling and improve the performance of implants, for example. Bioprinting requires an understanding of wetting properties in order to achieve optimal adhesion and structural functionality. On a side note, ramé-hart is also the world's leading producer of spinnerets used for bioprinting. Visit our spinneret website.

Coaxial bioprinting using a ramé-hart coaxial spinneret

4. Coating and Paint Applications: In industries such as automotive and aerospace, knowing the water contact angle on polymer surfaces helps in formulating effective coatings and paints. A surface with a specific water contact angle, for example, may be desired for its ability to repel water, prevent corrosion, or enhance the durability of coatings.

5. Self-Cleaning Surfaces: Understanding the water contact angle is crucial in the development of self-cleaning surfaces. Superhydrophobic surfaces, characterized by high water contact angles, can repel water and often self-clean by shedding contaminants, dust, or dirt.

6. Polymer Processing: Knowledge of the water contact angle can be important in polymer processing, such as molding and extrusion. It influences the wetting behavior of the polymer during processing, affecting the quality of the final product.

7. Printed Electronics and Microfluidics: In applications involving printed electronics or microfluidic devices, the water contact angle is significant for controlling the flow of liquids. It impacts the behavior of inks, adhesives, and fluids in these applications.

8. Surface Modification: Researchers and engineers often modify polymer surfaces to achieve specific properties. Measuring the water contact angle provides feedback on the effectiveness of surface modifications and surface treatments, helping to optimize and tailor the material for specific applications.

9. Quality Control: Water contact angle measurements can be part of quality control processes for materials. It ensures consistency and reproducibility in the surface properties of polymer samples, which is critical in industries such as manufacturing.

In short, understanding the water contact angle on a particular polymer sample provides insights into its surface properties, influencing its performance in a wide range of applications. This information guides material design, process optimization, and the development of advanced materials with tailored surface characteristics.

If you require a state-of-the-art contact angle goniometer in order to measure the water contact angle on your polymer samples for any of the reasons outlined above, don't hesitate to reach out to us. We'd love to hear from you.


Carl Clegg
Director of Sales
Phone 973-448-0305
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