What are the Best Practices for Surface Tension Measurement?

  • The best results for the pendant drop methods come when the droplet is at the cusp of detaching from the capillary. At this point, the droplet is significantly “deformed”; taking a raindrop-like shape.
  • This is because the surface tension of the droplet is trying to resist the force of gravity stretching the droplet. Thus, when the droplet is significantly deformed, surface tension is pushed to its limits. measuring the surface tension here will give the best results.
  • The best approach for generating a well deformed drop is:

1. Slowly increase the volume and remember the shape of the drop just before the drop detaches from the needle.

2. Generate a second drop with the similar shape as the last one before detaching.

  • The criterion deciding the volume is whether the liquid drop is well deformed (not a spherical shape). 
  • Generally, a larger needle will help with this. We suggest using a flat head needle with a diameter larger than 1.75mm.
  • Also, be as accurate with the image calibration number (measurement of the outside diameter of the needle) as possible.
  • Capture the images quickly after the droplet is generated, to avoid contamination as the droplet is suspended in air.

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