This is an investigation of the effect of paper-yellowing inhibitors on the rheological, colloidal, and interfacial properties of paper-coating liquids and the associated changes in the liquid surface microstructure. In addition to rheological measurements, we measured the zeta potential and imaged the surface microstructure of coating liquids by transmission electron microscopy (TEM) using an advanced Pt/C replica technique. The zeta potential is related to the concentration of added inhibitors. The images reveal interparticle structuring with increasing concentration of inhibitors. The structuring is related to the interaction between the coating liquids and the inhibitors. It was also found that the viscosity and the elastic modulus increased with inhibitor concentration. The significant changes in mixture properties due to the additives show the importance of the rheological and surface characterization of liquids and the ensuing effect on the corresponding engineering process. (C) 2003 Elsevier Inc. All rights reserved.