Contact Angle Measurement

The Contact angle, where a liquid/vapor interface meets a solid surface[wiki], has been widely used to measure the wettability of a surface in physics and chemistry. Scientists place a drop on a surface of interest, take an image of the drop in profile, and measure the angle the drop makes with the surface. We have developed a Contact Angle Measurement plugin for the ImageJ image analysis framework, which provides researchers a easier way to access experiment data. The major goal of our algorithm is to automatically detect drops and surfaces via image analysis, so that we can calculate the contact angle. Firstly, we filter the image by detecting edges and randomly sample a collection of three points on edges to get a collection of circles (note that three points define a circle)which could potentially fit the drop; then we apply various mathematical analyses to adjust the radius and position of the circle to gain a better fit. After the circle detection, we apply linear regression analysis to determine where the surface is. This approach turns out to be very reliable when the input drop region chosen by users is fairly small