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January 2020

Ten things to measure with your ramé-hart Goniometer in 2020
It's a new year and what better time to start measuring new things than now. We're here to help you get a good start in 2020 and not just for the fun of it - but to actually better characterize the materials you are working with and wish to evaluate. Here goes:

1. Contact angle. We've been measuring contact angle for nearly 60 years. In fact, our original ramé-hart Model 100 was the world's first commercial contact angle goniometer.1 Today all of instruments are camera-based and software-driven. Those who used our first instrument might say, "You've come a long way, baby." With our DROPimage Advanced software, contact angle resolution is now 0.01° and precision has never been higher. It doesn't matter what model you have since all of our instruments measure contact angle.2

2. Advancing and receding contact angle using the add/remove volume method. This method, like static contact angle, can be performed with any model instrument we sell.3 However, if you have an Automated Dispensing System, p/n 100-22, then it becomes much simpler.4 The difference between the advancing and receding contact angle is the...

3. Contact angle hysteresis. When the contact angle hysteresis is small, we conclude that the surface is rather homogenous with regard to to both chemical as well as structural composition.

4. If you have an Automated Tilting Base, then you can measure the advancing and receding contact angle using the tilting plate method.5 Most experts prefer the tilting plate method over the add/remove volume method for two reasons. First, the receding contact angle is more accurate since it's geometry is not disturbed by the presence of a needle. And second, the tilting method also provides us with the...

5. Roll-off angle. The roll off angle and the contact angle hysteresis are typically both small when the surface is superhydrophobic and the drop is in a Cassie state.6 By contrast, a drop in the Wenzel state tends to exhibit a large hysteresis and roll-off angle. This is due to the drop being embedded in all the nanoscopic nooks and crannies on the surface and not as prone to move. 

6. Surface tension is the property of a liquid that allows water striders to walk on water and drops to bead up on superhydrophobic surfaces. We've been measuring surface tension for over thirty years. However, until a year ago, the only way to measure surface tension with a ramé-hart tool was with DROPimage Advanced.7 A year ago we introduced our new DROPimage Pro software (which replaced DROPimage Standard). DROPimage Pro can now measure surface tension as well using our new Surface Tension Tool.8

7. Related to surface tension is interfacial tension which is the surface tension between two immiscible liquids.9 If the drop phase is less dense than the external phase, you would need an inverted needle. You will also need an Environmental Fixture or Quartz Cell. You can now measure interfacial tension also with DROPimage Pro as well as DROPimage Advanced.

8. Surface energy10 is understood to be the excess energy at the surface of a solid compared to the energy of the bulk material. It's typically measured by taking contact angles using different liquids and then evaluating the results using a variety of different formulas. Both DROPimage Pro and DROPimage Advanced include a suite of surface energy tools used to characterize solid surfaces and report surface energy.

9. Surface dilatational elasticity and viscosity are valuable rheological properties which can be measured using a ramé-hart Oscillator. Studies using these metrics can help determine the impact of surfactants and their concentrations on surface properties.

10. Dynamic contact angle is one of those types of measurements that our DROPimage Advanced software relishes. With the video replay feature11, each frame can be played back individually or in series. Measurements can be retaken using a different method. It's a highly flexible and powerful tool for any type of time-dependant study - not just contact angle, but dynamic surface tension12 and dynamic interfacial tension can also be measured.

1 For a brief history of the ramé-hart Goniometer, see this compelling article.
2 If you have DROPimage Advanced, consult this video for step-by-step instructions on measuring contact angle. Even if you think you know what you're doing, you might be surprised to learn something new. For DROPimage Pro or Standard, consult this video and this video is for DROPimage CA.
3 For the manual method, check out this video which is using DROPimage CA. The method will also work with any other edition of DROPimage.
4 For the automated method, see this video which requires the Automated Dispensing System.
5 This video shows the tilting plate method using the Automated Tilting Base.
6 More on Cassie and Wenzel here.
7 This video walks through a surface tension measurement using DROPimage Advanced.
8 To see the Surface Tension Tool in action with DROPimage Pro, check out this video.
9 To see interfacial tension work, watch this one.
10 AKA, surface free energy.
11 See this video for an example of dynamic contact angle with video replay.
12 See this video for dynamic surface tension.

Happy New Year 2020
All of us here at ramé-hart instrument company would like to wish you and your team a healthy and prosperous 2020. We're here to serve you and help you be successful in your analysis of surfaces and wetting properties. We look forward to being of service to you in 2020 - our 59th year helping scientist and researchers measure the items detailed in the article above. Happy New Year.

Carl Clegg
Director of Sales
Phone 973-448-0305
Contact us


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