RHEOLOGICAL PROBING OF STRUCTURE AND PIGMENT-RESIN INTERACTIONS IN MAGNETIC PAINTS

Dynamic rheological measurements are used to probe the structure of a model magnetic paint which contains iron oxide magnetic pigment partic les, a PVC wetting resin and an organic solvent. As the wetting resin concentration, c, in creases, the viscoelastic moduli, G' and G'', go through a minimum at c = c(0) which corresponds to the saturated adsor ption of the resin. At c < c(0) the paint is highly elastic, thixotrop ic and brittle (G' sharply drops, G'' goes through a strong maximum at high strain), which indicates the existence of a strong flocculated n etwork. At c > c(0) the moduli increase due to accumulation of free re sin. However, at high c the paint becomes less elastic, less brittle a nd less thixotropic, which indicates that the structure formation in t his case is dominated by small aggregates rather than a network.