Adsorptive behavior of surfactants on surface of Portland cement

On the surface of Portland cement, four surfactants have different adsorpti ve behaviors: ethoxylated fatty alcohol sulfate (AES) belongs to the lignos ulfonate (LS)-type of adsorption; cetyl piridinium chloride (CPC) is kineti cally controlled; condensates of naphthalene formaldehyde (NS) have a linea r relationship of adsorbance vs. concentration; and ethoxylated alkyl pheno l (TX-10) is not adsorbed. All adsorbed surfactants have their hydrocarbon chain toward liquid phase and an increase in hydrophobicity of the cement s urface. However, AES suffered a change of hydrophilic --> hydrophobic --> h ydrophilic because of the formation of adsorptive micelles. Both AES and NS only increase zeta potential, but CPC changes zeta potential from negative to positive. A modified Stem double-layer model has been proposed to illus trate adsorptive characteristics of the above surfactants. (C) 2001 Elsevie r Science Ltd. All rights reserved.