Contact angle measurement
Contact angle measurement is used to evaluate surface wettability, which is an important characteristic in the development of new hydrophobic materials, such as waterproof textiles, polymers, paints, and coatings.
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What is contact angle measurement?
The contact angle is a value demonstrating the wettability of a solid material by a liquid. It describes in detail how a liquid spreads over a surface. In theory, contact angle can form values between 0° and 180°. Values close to 0° represent complete wetting, values at 45° are referred to as good wetting, and values over 90° mean the material is not wettable. If the contact angle exceeds 150°, the material can be classified as superhydrophobic. Contact angle measurement can be executed with several different methods, and method selection depends on the various parameters. Drop shape analysis, Wilhelmy-Plate, and top-view distance are some of the well-known measurement techniques.
Why measure contact angle?
Wettability (hydrophilicity vs. hydrophobicity) is an important parameter in industries including paint, coatings, textiles, and construction materials. For example, self-cleaning materials and waterproof fabrics need to be analyzed with contact angle measurement to evaluate their performance.
How is contact angle measured?
Static contact angle measurement is the most common method that utilizes the sessile drop method. In this analysis, a contact angle goniometer and a high-resolution camera are used to capture an image of the drop sitting on the surface from the side view. Analyzing the image will reveal the contact angle.
In contrast with the static contact angle, where the three-phase boundary is static, it is also possible to measure dynamic contact angles. Dynamic contact angle measures the characteristics of a moving drop of liquid on a surface. Dynamic contact angles are presented as receding and advancing angles, depending on the direction of where the drop of liquid is moving. The movement of the liquid drop is usually initiated by tilting the solid surface where the liquid drop is placed. The angle of contact where the drop begins its movement is referred to as the roll-off angle. The dynamic contact angle, as well as the roll-off angle, can be measured with the tilting method.
Which factors affect the contact angle?
Contact angle measurement is susceptible to different internal and external factors. For example, surface roughness, density, and relative moisture content can affect the eventual contact angle measurement results. Both sample contamination and the method used to clean it can have a considerable impact on the results.
An example of a typical contaminant is grease stains from fingerprints. It is never advised to clean the sample with surfactants as a thin barrier will stay on the surface after rinsing and influence the results. Contact angle measurement can also be affected by static electricity. If the sample surface is rinsed and subsequently rubbed dry, static electricity can build up on the surface and alter the measurement results.
The type of liquid chosen to be used in the measurement also has a significant effect on the measured contact angles. Water is the most commonly used liquid and it is advisable to use well-purified water, for example, HPLC-grade or double-distilled water. The same applies to other test liquids.
Contact angle test liquids should always be stored in such a way that neither the composition nor properties of the liquid alter over time. For example, liquids sensitive to visible light should be stored in amber containers in the dark. It is not recommended to use plastic containers, as plasticizers can migrate to the liquid and influence its properties.
In optical measurements, there is a list of factors that affect the measurement of contact angle, such as image size, resolution, contrast, light levels, and depth of field.
Sample requirements and preparation
To get the most accurate and reliable results from a contact angle measurement, it is necessary to prepare the samples with great care. A good practice is to clean and dry the sample material in such a way that it becomes as clean and neutral as possible. In repeated measurements, the same spot should never be used. Even with careful handling, cleaning, and drying, the sample will be affected by the placement of the drop, and subsequent measurements can produce inaccurate results.
Need a contact angle analysis?
Measurlabs offers contact angle testing services with fast results and competitive prices. If you have any questions about your sample or its suitability for the method, our experts are always happy to help. You can contact us through the form below or at firstname.lastname@example.org.
Suitable sample matrices
- Coatings & paints
- Paper & board
Ideal uses of contact angle measurement
- Hydrophilic/hydrophobic properties
- Alterations in wettability with different treatments
- Surface energy
Frequently asked questions
Contact angle measurement can be used to understand the surface energy, wettability, and hydrophilic/hydrophobic properties of a material. It is often used in the paper-, board-, textile-, coatings-, and metallurgical industries.
Suitable sample materials include, for example, metals, ceramics, polymers, fabrics, coatings, paints, paper, and board.
Measurlabs offers a variety of laboratory analyses for product developers and quality managers. We perform some of the analyses in our own lab, but mostly we outsource them to carefully selected partner laboratories. This way we can send each sample to the lab that is best suited for the purpose, and offer high-quality analyses with more than a thousand different methods to our clients.
When you contact us through our contact form or by email, one of our specialists will take ownership of your case and answer your query. You get an offer with all the necessary details about the analysis, and can send your samples to the indicated address. We will then take care of sending your samples to the correct laboratories and write a clear report on the results for you.
Samples are usually delivered to our laboratory via courier. Contact us for further details before sending samples.