Viscosity of monophase addition silicones as a function of shear rate.

The viscosity of monophase addition silicone impression materials was measured as a function of shear rate. The setting of mixed catalyst and base was prevented by addition of a small amount of phenyl propiolic acid. All products showed a 6- to 10-fold decrease in viscosity with an increasing shear rate (shear thinning). The addition of phenyl propiolic acid had little or no effect on the viscosity of three materials. However, when added to the catalyst or base only of two products, it increased their viscosity and exaggerated the shear thinning effect.