iPhone App

Free iPhone App for simple measurement of contact angles

Measuring contact angles can be a significant challenge, if you don’t have dedicated equipment and the experience to use it. This challenge we encounter often with our customers, who have difficulties measuring the contact angle after coating their device with our hydrophilic coatings. To overcome this challenge we developed an iPhone App that enables simple and accurate measurement of contact angles. The measurement can be done wherever you are, simple, fast and without dedicated equipment.

The App is made freely available to our customers, and anyone who would like to measure contact angles.
You can get the App in the App store, just make a search for “Joninn – contact angle measurement”.

App details

Overall use of the App

  1. Place a water droplet (of known volume) on the surface to be analysed.
  2. Place a ruler with millimeter markings next to the droplet.
  3. Take a photo of the droplet and ruler.
  4. The App analyses the photo and give you the contact angle.

Working principle

The App uses a modified Bikerman method, to calculate the contact angle (CA) from a smartphone photo.
The Bikerman method is only suitable for hydrophilic and neutral surfaces.

  • For CA less than 75° it works great.
  • For CA between 75° and 85° it has limited accuracy.
  • For CA above 85° it is unsuitable.

Photo to be analyzed
The Photo to be analyzed must be taken from directly above the droplet, and the photo must include a ruler with millimeter markings.
When taking the photo, you will get the highest accuracy of the calculated contact angle by ensuring that:

  • The droplet should be at least 10% of the photo width.
  • The contour of the droplet is in focus and has high contrast to the background.
  • Adjust the light to avoid shadows and very bright spots in the photo.
  • A single color background (such as a piece of paper) works best. Especially if the surface to be analyzed is transparent.
  • If possible use a high contrast test liquid (such as our TL1).
  • The ruler should be oriented horizontally or vertically in the photo. Get as close as possible to 0° or 90° orientation as possible.

Critical review of results
Due to the varying quality of the photos recorded, the measured contact angles shouldn’t be trusted blindly.

  • You will get an indication of the accuracy of the measurement from the mean, minimum and maximum estimates of the CA on the results page. If these estimates differ significantly, then the accuracy will be poor.
  • You will also get an indication of the accuracy of the measurement from the circles overlaid the photo. If these differ significantly from the actual droplet, then the accuracy will be poor.
    If you often get poor results, then you must adjust the light conditions to give a higher quality photo.
  • If either of the two circles are clearly off the droplet, you should only use the other result.
    – The purple circle corresponds to MaxCA.
    – The green circle corresponds to MinCA.

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