Adsorptive behavior of surfactants on surface of Portland cement

On the surface of Portland cement, four surfactants have different adsorptive behaviors: ethoxylated fatty alcohol sulfate (AES) belongs to the lignosulfonate (LS)-type of adsorption; cetyl piridinium chloride (CPC) is kinetically controlled; condensates of naphthalene formaldehyde (NS) have a linear relationship of adsorbance vs. concentration; and ethoxylated alkyl phenol (TX-10) is not adsorbed. All adsorbed surfactants have their hydrocarbon chain toward liquid phase and an increase in hydrophobicity of the cement surface. However, AES suffered a change of hydrophilic --> hydrophobic --> hydrophilic 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 illustrate adsorptive characteristics of the above surfactants. (C) 2001 Elsevier Science Ltd. All rights reserved.