The production of stable hydrophobic surfaces by the adsorption of hydrocarbon and fluorocarbon carboxylic acids onto alumina substrates

The adsorption of various carboxylic acids onto alumina substrates has been studied as a model system for the study of the long range hydrophobic inte raction. The adsorption was studied using classical adsorption isotherms, c ontact angle measurements and colloid probe atomic force microscopy. Carbox ylic acids form esters with the hydroxyl groups present on the alumina surf ace and produce surfaces with a range of hydrophobicities and stabilities d epending on the acid's functionality. Hydrocarbon carboxylic acid adsorptio n was found to be adequately described by the Langmuir adsorption model and produced stable surfaces of varying hydrophobicities which resisted dissol ution by water. By comparison, hydrophobic surfaces produced with fluorinat ed acids adsorbed from aqueous solution were not always stable, although th eir stability was greatly improved when the chemisorption was carried out i n a non-aqueous solvent at elevated temperatures. Adsorption of these fluor inated carboxylic acids produced the most hydrophobic surfaces. Interaction forces between alumina surfaces coated with adsorbed propionic acid were a s expected from DLVO theory with no evidence of hydrophobic forces. (C) 200 1 Elsevier Science B.V. All rights reserved.