Coating components are subject to particle-particle, particle-solvent, and particle-polymer interactions. Van der Waals forces, electrostatic repulsions, and steric stabilization are the reasons for these interactions. Importantly, the characteristics of adhesion and cohesion between the components form the base coating structure. Calcium carbonate and kaolin are commonly used pigments. Pigments support a structure of fine porosity and form a light scattering surface. The surface charge of the pigment plays an important role in dispersion consistency. The surface charge of calcium carbonate is negative and not dependent on pH, however it can decompose under acidic conditions. Kaolin has negatively charged faces while the charge of its laterals depend on pH, being positive in acidic conditions and negative in basic conditions with an isoelectric point at 7.5. The equation for determining the isoelectric point is as follows:
In the papermaking process, the pigment dispersions are generally kept at a pH above 8.0.