Discussion Forum

Hi,

I am not sure if I understand your question correctly. You have an image of a sessile droplet sitting on a surface and you want to determine the contact angle from this image?
If this is correct then you need some kind of image processing procedure. This is certainly not the scope of COMSOL. COMSOL solves systems of PDEs on a finite element grid. You may be able to model a sessile droplet if you know the surface and droplet properties. That's a different story.

Cheers
Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com

Hi,

Molla: in COMSOL (with CFD or Microfluidics Modules, see www.comsol.com/products/specifications/fluid-flow/) you can find the physics "Two Phase Flow", in which you can set (not estimate!) the contact angle in a boundary by means of the "Wall" boundary condition, specifically "wetted wall".

Thus the contact angle is an input to the model. As you know, it depends on the pair of materials (liquid-solid) and can be found in the literature.

But it would be nice if somebody has an idea of the opposite: from the materials properties, to simulate a liquid-solid contact problem and then measure the contact angle, as an output. Has anybody got any idea about this?

Hi Mr. Kaiser,
Thanks for your valuable reply. Yes you understood the problem quite right. I also talked with one of my professors, works with comsol, and he replied me the same. Actually I've to detect the edge of the droplet first. It looks like a semicircle. Then I've to draw a tangent which gives me the contact angle.

and as Jesus mentioned once you have that angle measured you can use it as in input in COMSOL in two-phase flow simulations.

hey i am also working on a similar problem. has anyone been able to find a solution to find the contact angle. kindly help.

Hey,
I am working on the same problem.Has anyone figured it out yet?

To estimate the contact angle, follow the procedure explained by "Jesus". You need to guess the contact angle, run the simulation, and compare the shape of the droplet with the image that you've acquired. You have to repeat this procedure until you get the closest shape to the experimental shape (Error is minimum).

However, keep in mind that:

The contact angle that you obtain here is an estimate, which is based on the theoretical force balance at the droplet interface. These forces are simplified and may be different to some extent from those in real world. The contact angle that you obtain by this procedure can also be affected by numerical errors due to deformation of the geometry, ... and singularity near the contact line.

Thus,
As "Edgar" suggested, try to double check your calculated contact angle by using image processing software as well. Once they agree, then accept the calculated value.

Good luck.

I would suggest using ImageJ as the image processing software because it is quite useful and has in built functions to make measurements like these.