DLVO theory applied to TiO 2 pigments and other materials in latex paints

Abstract

Understanding how a paint formulation translates into comparative numbers of particles, how the spacing between particles compares to their size and what controls their stabilization mechanisms improves efficient formulation design. The application of Derjaguin, Landau, Verwey and Overbeek (DLVO) theory of the electrostatic stabilization of colloids is reviewed by calculating the inter-particle potentials for typical titanium dioxide pigment particles in a conventional aqueous paint formulation. The calculations show that composition and structural details of the particles need to be input, in order for DLVO theory to model the stability of the pigment particles. It is necessary to include the extent of the surface treatment on the pigment particles, the ionic strength of the continuous phase and the thickness of any adsorbed layer of dispersant polymer as well as knowing the zeta-potential of the particles under the prevailing conditions. Ionic strength determines the range of DLVO forces, so the conductivity of various salt solutions was determined in order that ionic strength could be measured from simple determinations of paint conductivity. Other calculations compare the likely stability of an extender and a typical latex to that of the pigment particles in both DLVO calculations and in calculations of settling rates. The spacing between particles in a random dispersion is estimated from their particle sizes, their concentrations and the characteristic packing fraction assigned to the dispersion.