Measurement of contact angles from the maximum diameter of non-wetting drops by means of a modified axisymmetric drop shape analysis

A modified axisymmetric drop shape analysis approach, ADSA-MD (maximum diameter) was developed to measure the contact angles of non-wetting drops front top-view images of the drop. The approach numerically solves the Laplace equation of capillarity given the following input parameters: maximum diameter and volume of the drop, liquid surface tension, density difference between the two fluid phases and the gravity constant. The computed contact angles are in good agreement with those from ADSA-P, an approach which uses the profile of the drop to determine the contact angle. This new technique is particularly suited for systems where the quality of the solid substrate is poor, such as in the case of biological systems. For these situations contact angle determination from the profile is difficult, if not impossible, due to the difficulty in locating the three-phase contact line. The ADSA-MD approach was used to determine the contact angle of water sessile drops on colon sections of New zealand white rabbits.