The sessile drop method is an easy and fast method used to measure the contact angle between solids and liquids. The value of the contact angle is used in surface characterization, in particular the wettability of solid surfaces by the liquid and to calculate the surface free energy. In this work, we study the effects of the volume of the drop placed on the surface, the elapsed time between drop placing and measurement and the cleaning of the substrate (not cleaning, washed with ethanol or washed with acetone) in the value of the contact angle on Ti6Al4V and AISI 316 stainless steel. We found that drop asymmetry is a very important parameter that must be considered in CA measurements. Anasymmetry parameter used to qualify the drop asymmetry is proposed. It was also found that the degree of cleanliness produces dispersion in the contact angle values; on the other hand no differences were found between cleaning with ethanol or acetone. CA decreases with time and increases slightly with decreasing droplet volume.Fil: Schuster, Jonathan Maximiliano. Provincia de Misiones. Comite de Desarrollo E Innovacion Tecnologica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; ArgentinaFil: Schvezov, Carlos Enrique. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; ArgentinaFil: Rosenberger, Mario Roberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnológico Nordeste. Instituto de Materiales de Misiones; Argentin

Surface Free Energy (SFE) of solids should be calculated using theoretical models. The contact angle (CA) measurement on a surface is considered the most practical way to obtain the SFE. The results of five methods based in the models are compared: the method of Zisman (ZI), the geometric mean (GM), the harmonic mean (HM), the Lifshitz-van der Waals/ Acid-Base (LW/AB) and the equation of state (ES). The SFE calculated with GM, HM and LW/AB methods change with the amount and type of liquid used, however, when water, glycerol and dimethyl sulfoxide are used together the SFE and its dispersive and polar components are similar in value for the three methods. In the case of the ES model the values of SFE change with the liquid used; finally using the ZI method the SFE values are 20% lower than the values of SFE obtained with the other methods