Contact angle with cell phone

This page gives instructions on how to use your cell phone to take contact angle measurements.

Experimental Instructions

Put your sample on a flat substrate
Use a micropipette to deposit a small droplet of fluid on the sample
Take a picture of the droplet from the side of the substrate as shown in Figure below. Make sure the image is in focus and not blurry.

Install the open source imageJ plugin for contact angle measurements: https://imagej.nih.gov/ij/plugins/contact-angle.html
Open imageJ and check to see if "Contant Angle" is available under the "Plugins" tab and select it.
Open the image.
Select the two end points of the droplet where it meets the substrate using the "drop points" button.
Select 5 points along the droplet surface and allow imageJ to run the fitting algorithm.
Click on the Menu button in the Contact Angle plugin toolbar.
Click Manual Points Procedure.
Open the results window to see the contact angle for a spherical approximation and also for elliptical approximation.

This will not work if the substrate is not absolutely flat. The program needs to be able to draw a straight line that follows the surface of the substrate exactly after the user selects the two end points of the droplet.
Uses either a spherical or an elliptical approximation for the droplet. The user needs to be able to pick manually which approximation works better for their case.
The drop has to be very very small (ideally <3ul). The program neglects gravity.