A high-accuracy polynomial fitting approach to determine contact angles

An automated polynomial fitting (APF) scheme is presented for high-accuracy contact angle measurements. The APF method acquires highly magnified (e.g. 35×) images of a drop and extracts the drop profile using image processing techniques. Then a polynomial is fitted to the experimentally observed drop profile and the contact angle is calculated using the slope of the polynomial at the contact point. Different edge detection techniques were examined and it was found that the Laplacian of Gaussian edge detection method performs well for the highly magnified images. A thorough statistical analysis was carried out to determine the optimum parameters for the curve fitting e.g., the order of the polynomial and the number of pixels used in the fitting procedure. A comparison of the APF method with Axisymmetric Drop Shape Analysis (ADSA) indicates good agreement between the two methods. The APF method is applicable to a variety of situations, e.g., liquid lens systems, non-axisymmetric drops, and electrically charged drops, where application of traditional contact angle measurement methods may not be accurate enough.