Difference between three calculated results for super-hydrophobic surface from different manufactory

For a better assessment of the function of commercialized drop shape analysis software, especially for analyzing the contact angle of super hydrophobic materials by sessile drop method and for surface tension between liquid –gas based on sessile drop method by using Young-Laplace equation fitting method，by the way to test performance of Young-Laplace equation fitting method , we had a contrastive analysis on partial business drop shape analysis software. During analyzing process, we adopt a liquid drop picture of the same piece of super hydrophobic material（the value of its contact angle is about 160°）.

Through visiting the hyperlink as below you can download the picture that we used for analysis, what calls for special attention is that the existing picture is of PNG format. You have to transform it into a picture of bmp format by Photoshop with 8 bit format, then you can apply it to the software of Kruss and Dataphysics.

You also can download image by saving images below:

The image magnification factor is 0.0115mm/pixel or 85.96 pixel/mm.

1, first, we analyzed the picture with the drop shape analysis software—DSA1.9 from Kruss, and the screenshot of calculating process is shown as below:

From the screenshot, we can find out contact angle is about 167.2°and surface tension is about 53.55mN/m .The calculating method we adopted is Young-Laplace equation fitting method.

We can assess the fitting result by enlarging fitting picture. We found that the right side of the fitting curve did not match with the found drop edge curve, so the fitting is not successful. So we got the point that the calculated contact angle value does not accord with the actual value.

2. We analyzed the contact angle and surface tension of same picture with the drop shape analysis software- DSA3.0 from Kruss.
Screenshot of analyzing process is shown as below:

From the screenshot it is observed that, the calculated result by Young-Laplace equation fitting method is that contact angle meter value is 169.8 ° and surface tension value is 53.62mN/m. It is almost same with value that our first time calculated which adopted DSA1.9. Identically, in the enlarging fitting picture, we found that the right side of the fitting curve did not match with found drop edge curve completely.

3. We had a comparison test on same picture by drop shape analysis software - SCA2.0 from Dataphysics, and the screenshot of the test is as below.

From the screenshot it is observed that when SCA2.0 adopting Yong-Laplace equation fitting, the calculated result is 168.48°. This value is similar with the result from software DSA from Kruss. but ,the surface tension value calculated by SCA2.0 is a little different from one got from Kruss, which is 49.93mN/m. At the same time, we can found that when we are enlarging the picture of fitting part, the fitting curve of SCA2.0 do not accord with found drop edge curve. And what`s worse is that the fitting curve of software SCA2.0 is not a smooth curve. There is obvious polygonal lines phenomenon.

4, At last, we had surface tension and contact angle analyses on same picture with CAST3.0 from KINO.
Screenshot of analyzing process is shown as below:

From the analysis results. The contact angle value calculated by CAST3.0 is 160.79°, which is much closed to the real value. And the calculated surface tension value of water is 70.26mN/, which is also very closed to the surface tension value of distilled water at temperature 30 ℃. But from the analyzing results, we found that there is distinction of contact angle vale and surface tension value between the left side and the right side of the fitting. This is mainly because the sample inclined 0.5°, result in advanced angle and receded angle. So there is a small error between the calculated value and the real value, but the error will be acceptable. And from the enlarged picture during fitting process it is observed that the contact ratio between fitting curve and margin locating curve of CAST3.0 is the best among all commercialized drop shape image analysis softwares.it is shown as below:

So, through a comparison of the drop shape analysis software, function for fitting non-axisymmetric drop shape especial for measurement of super-hydrophobic surface is necessary while axisymmetric drop shape analysis (ADSA) will be failure, because advanced and receded contact angle will not keep same for super-hydrophobic surface when surface is not level and yes it will be hard to keep completely level for sample.