An easy way to measure surface free energy by drop shape analysis

Abstract The drop shape analysis is a conventional method to evaluate wettability and surface free energy. The analysis of drop profile is commonly used for the contact angle measurement between the liquid drop and sample surface. In many cases such as confined surfaces, it is difficult to carry out this measure, therefore it is necessary to evaluate the shape of the drop from top view point. The aim of this work was to develop a procedure in order to measure wettability and surface free energy values by means of the analysis of the drop shape from top view point. Starting from Tadmor equation, a polynomial function was obtained to correlate the drop diameter to its contact angle on a flat horizontal sample surface. In addition, analyses were carried out in order to study the shape of liquid drop varying the tilt of sample surface. In this case was shown a correlation between the tilt grade and the maximum characteristic lengths (parallel and orthogonal to pitch) of a drop shape on a tilt surface sample. Using the maximum characteristic lengths and a polynomial function previously obtained, it is possible to establish values of pitch, surface free energy and wettability of sample surface. In order to confirm the developed procedure, tests on three different materials have been performed obtaining these three performance indexes. All results obtained by means of this alternative analysis have been compared and corroborated by the classical method using the contact angles of the drop analyzed from a lateral view.