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|Overcoming the Limitations of Contact Angle Goniometry|
The most common method for measuring
wetting behavior is contact angle goniometry. In short, the profile
view of a sessile drop on a surface is captured. The angle between
the surface and the tangency of the drop is measured. In the
overwhelming majority of cases, this method works well and produces
precise and accurate results. Here at ramé-hart, we've been doing
contact angle goniometry for 60 years. In fact, we were the
first company in the world to make a commercially available contact
angle goniometer. Our first instrument was based on the design of
Dr. William Zisman of the Naval Research Lab.1
Nonetheless, there are conditions in which traditional contact angle goniometry fails to deliver. Take a drop that is sitting on a recessed surface - one which prevents the capturing of a side view image. This can be a challenge using conventional methods. To overcome this obstacle, we developed an Overhead Optical Imaging Kit. This product can be added to any ramé-hart goniometer with DROPimage Advanced. The method permits the user to take a picture of the drop from the top view. The software then calculates the contact angle based on the volume of a partial sphere and as calculated by the two-dimensional top view and the drop volume which can very precisely dispensed using the ramé-hart Automated Dispensing System.
Likewise, the Overhead Optical Imaging Kit is useful for extremely hydrophilic surfaces where the contact angle is under 5°. In this conditions, it's particularly challenging to obtain a good measurements using the traditional side-view method. However, the overhead method makes the capture of accurate contact angle measurements quite effortless by comparison.
Another challenge is capturing initial contact angle on surfaces that do not promote static measurements. Perhaps the surface is absorbent (e.g., wood or paper) or perhaps the solid/liquid combination results in dynamic wetting. In both cases, it's often critical to capture the contact angle at the precise moment of drop deposition. To achieve this, we've developed the trigger feature. This video shows how easy it is to incorporate the trigger command in a contact angle measurement. If dynamic contact angle is measured - as shown in the video, the rate of absorption can also be easily measured.
Another challenge is reflective surfaces. The baseline snap tool does not work well in these conditions. However, the baseline can be positioned manually. You can also make a microdrop to position the baseline and lastly, the baseline can be positioned midway between the pendant drop and its reflection. To check out these three tips, visit this video.
Lastly, there are times when we wish to leave the needle embedded in the drop while taking measurement - for example, when doing advancing and receding contact angle measurements using the add/remove volume method. For this we have the Right line option. This video shows how to properly use both the Right line option as well as the Red line option.
These obstacles represent the majority of cases where conventional contact angle goniometry can be a challenge. Yet we've been working for years on ways to overcome these obstacles. The above points are only some of the ways that we make contact angles easier to measure. If you're having any challenges, please reach out to us and let us know the nature of your quandary. If we have a solution, we will share it with you. And if we don't have a ready solution, we'll work on one.
|Happy New Year|
2020 proved to be a challenging year.
In March our business came to a halt. During the ensuring months,
we've climbed back to nearly full production. We're proud to report
that in the Spring we provided instrumentation and parts to
researchers who have been using our products to develop solutions
for combating COVID-19. In addition to contact angle goniometers and
tensiometers, we also make
spinnerets that are used extensively in 3D bioprinting, medical
electrospinning, and core-shell nanofiber production.
We look forward to returning to some semblance of normality in 2021 as I'm sure you do too. So, Happy New Year. May 2021 bring you happiness, prosperity, and a safe vaccine that can help bring an end to this pandemic. Cheers.