WETTING OF SOLIDS BY SOLUTIONS AS A FUNCTION OF SOLUTE ADSORPTION1,2

The wetting of flat platinum and chromium slides of small surface area by aqueous solutions of decylamine was measured as a function of the adsorption of the amine and the surface tension of the solutions. Adsorption at the solid- solution interface was measured in situ by an optical polarimetric method and wetting was determined concurrently by contact angle measurements employing the captive bubble technique. Adsorption and wetting results for platinum were sharply defined but those for chromium were somewhat obscured by erratic kinetic effects. Multilayer adsorption was observed in all cases, and isotherms on platinum in basic solutions exhibited steps. The observed contact angles of the solutions on platinum rose from 0 deg to a maximum of about 90 deg as adsorption increased, and then fell, sometimes to 0 deg , as adsorption proceeded further. A model is proposed to explain the wetting results which provides a semi-quantitative scheme for computing the behavior of the contact angles from the adsorption isotherms. (auth)