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ramé-hart Newsletter

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May 2017

  A Dozen Things You Can Measure with a ramé-hart Goniometer / Tensiometer
  Let's face it, we've been around for a long time. We opened our doors in 1961 and not long after that we started building the world's first production contact angle goniometer. That first instrument was called the NRL Model 100-00 and was based on the design and work of Dr. William Zisman at the Naval Research Laboratory (NRL).1 We made thousands of them. Hundreds are still in use today. And perhaps because of that first instrument, which really only measures contact angle, we are often thought of as experts in contact angle. While that's certainly true, we'd like to expose you to a wider array of our surface characterization capabilities beyond goniometry. Thus, the goal of this month's newsletter is to detail a dozen different things you can measure with a current-generation ramé-hart Contact Angle Goniometer / Tensiometer.

1. Let's start with Contact Angle since it's what we started with and it's still the most common method for characterizing the wetting properties of solid surfaces. Today's ramé-hart goniometer takes high-speed images (e.g., at 100 frames/second or faster) of the profile view of a sessile drop sitting on a flat surface and in real-time evaluates the contact angle formed at the three-phase line using curve-fitting algorithms. Surfaces with high surface energy are characterized by low contact angles. Any factor that lowers the strength of intermolecular interactions will also lower contact angle - such as contaminates, surfactants, or increase in temperature.

2. While the static contact angle is amazingly informational, the Advancing and Receding Contact Angles are even more valuable in determining the range of possible contact angles for a given solid/liquid system.2

3. When the Contact Angle Hysteresis, which is the difference between the advancing and receding contact angle, is small, this indicates that the surface is rather homogeneous relative to chemical composition, or structure (i.e., roughness), or both. The Automated Tilting Base is an indispensable option for this task.

4. Surface Energy is the property of a solid. Our DROPimage software (standard and advanced editions) includes a number of tools for measuring surface energy: Acid-Base Tool, Two-Liquid Surface Energy Tool, Multi-Liquid Surface Energy Tool, Zisman's Plot Tool, the Solid-Liquid-Liquid Tool, and the One-Liquid Tool.3

5. The Work of Adhesion determines an index of wetting ability of a liquid for a given solid. It's a force measurement that explains the work which is required to separate two phases. Moreover, it's the energy that is expended in the process of wetting.

6. Surface Tension is what cause the outer surface of a liquid drop to behave like an elastic sheet. Surface tension permits insects to walk on water and for drops of water to bead up on a surface. We measure surface tension with our DROPimage Advanced software via the axisymmetric pendant drop method using sophisticated computational algorithms.4

7. Surface tension is measured in an air or gas external phase. When the external phase is another liquid, the resulting measurement is Interfacial Tension.5

8. Rate of Absorption can easily be measured dynamically by logging the change in drop volume over time.

9. The Captive Bubble method producing an air bubble on the underside of a substrate which is immersed in a liquid (e.g., water). Our DROPimage software can be used to measure the resulting contact angle of the inverted sessile drop. This method is particularly suitable for engineered tissue, breast implants, contact lenses, disposable diapers and other products fabricated from hydrogels and superabsorbent polymers.6

10. Dewetting and Pinning properties can be captured by logging the width of a sessile drop as a function of time or volume.

11. Surface Dilatational Elasticity and Viscosity are measured using an Oscillator which provides periodic oscillatory deformation of sessile and pendant drops. The axisymmetric drop and bubble shape methods are used to measure these properties. Slower moving oscillatory measurements can be captured with the Automated Dispensing System alone.7

12. We can precisely Measure Distances of any feature that can be seen from the profile view and fit within the Field of View (FOV) which is, by default, 6.8mm wide by 5.1mm high.

No matter what your requirements are, we can help you configure a system that will not break your budget and that will take the measurements necessary for your application - configured with the necessary options and accessories. Please contact us for a no-obligation consultation and quotation.

1 For more on the history of ramé-hart, see our Dec 2007 Newsletter.
2 For more on advancing and receding contact angles, see our Jul 2010 Newsletter.
3 To watch Surface Energy measurements in action, check out this playlist.
4 To see Surface Tension in action, check out this playlist.
5 Here is a good interfacial tension video
6 Captive Bubble is shown in this video.
7 See oscillation in this video.
8 See how a ramé-hart instrument can be used as an optical comparator here.




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



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