ON THE USE OF WASHBURNS EQUATION FOR CONTACT-ANGLE DETERMINATION

A systematic study on the possibility of Young's contact angle determi nation from Washburn's equation was performed using the so-called thin -layer wicking technique in which the rate of penetration of a liquid into the porous layer of a solid is measured. Commercial (Merck) SiO2 deposited on the glass plate for thin-layer chromatography was used as a model solid and n-alkanes (from pentane to hexadecane), diiodometha ne, and alpha-bromonaphthalene were employed as the probe liquids, It was shown that the contact angle calculated from Washburn's equation w as not equal to Young's contact angle of a drop of the same liquid, pl aced on a flat surface of the solid. Consequently, the solid surface f ree energy components calculated using contact angles from Washburn's equation are not the true values. However, the approach previously sug gested by us has been verified again, as it gives consistent values of the surface free energy components determined from all the liquids us ed.