Which measuring method is the best for measuring contact angle?

If we download a sample image of contact angle of water drop from https://www.lpdlabservices.co.uk/analytical_techniques/surface_analysis/wettability/optical_contact_angle.php

Due to drop shape analysis softwares usually use BMP format, so you need to tranfer the image format from JPG to BMP by photoshop. Some softwares can only analysis 8 bit BMP images, so you  need to tranfer the image into 8 bit.

A, When you use DSA3.0 software to measure the contact angle, you can easy get the result as shown below:

1, Measuring contact angle using Circle fitting method:

You can find out that the fitting curve (green one) is not fitted the drop shape edge (Black edge of drop profile).So, the result of contact angle is not acceptable by the circle fitting method.

2, Measuring contact angle by Ellipse method.

The same error is happened when using Ellipse fitting method for measuring contact angle. Fitting curve is not coincide to the drop shape profile.So, for the same drop image, Ellipse fitting method is not robust method. And almost 80% images can not use the Ellipse method due to the drop shape is not always elliptic.

3, Young-Laplace equation fitting method for measurement of contact angle.

Fitting curve of left side is fitted to the drop shape but the right side is not fitted to the drop shape. So, if you just want to get a nearly value of contact angle, you can use the 161.1 to characterize your sample by this drop image.

But you cannot get more information, such as anisotropy of the structure of your sample. 

B, Measuring contact angle for the same drop image by software of Advance.

1, Using Young-Laplace Equation fitting method to measure contact angle of a drop shape.

The Advance and DSA 3.0 is from the same company, but the results are not same. And, we can find out that fitting curve is not same thick as the base line of the result and the fitting result of DSA3.0. It's too thick to judge to fitting effect ot drop shape. So, we believe that we cannot believe the result of Advance because it cannot tell you which drop shape is right fitted.

C, ADSA-RealDrop for measurement of contact angle.

We used ADSA-RealDrop from KINO to fitting the same image of drop shape.

The contact angle of left side is 161.794 and right side is 156.710. So due to the surface of sample is tilted, there exists the advanced and receded contact angle of the image of water drop. ADSA-RealDrop can tell you more.

And then, we come to the conclusion:

ADSA-RealDrop method is the best one for measuring contact angle. And it can be used to measure 3D contact angle. We can also use MicroDrop method to measure contact angle fiber.