Wetting and rheological characteristics of hydrophobic organic pigments in water in the presence of non-ionic surfactants

Wettability and rheological characteristics of highly hydrophobic organic pigments were determined in the absence and presence of surfactants. Two widely used pigments, carbon black (CB) and copper phthalocyanine blue (CuPc), were selected as model pigments. As wetting and dispersing agents, a range of non-ionic nonylphenol ethoxylated (NPE) surfactants with varying hydrophilic chain length was used in the tests. Wetting properties of the pigment powders were investigated by the contact angle measurements based on capillary rise method. Rheology experiments were carried out by a controlled shear stress rheometer. Rheological properties of pigment suspensions were determined by applying common rheological models to shear stress (τ) versus shear rate (γ) plots. The experimental results demonstrated that, highly ethoxylated surfactants were more efficient than less ethoxylated surfactants in reducing contact angle of pigment powders. Finally, it was inferred that CB and CuPc suspensions behaved virtually as Bingham plastic and shear thickening (dilatant) type suspensions, respectively.