Analysis of non-ionic surfactants on the rheological and interparticle response of polymer enhanced colloids for investment casting slurries

Dispersion of ceramic slurries for investment casting is governed by the colloidal solution and influenced by surfactants, where micelles form until a critical micelle concentration (CMC) is attained. Light scattering techniques and rheological methods were used to determine the CMC of three different non-ionic surfactants. The former provides an insight into the: zeta potential; electrical conductivity; and hydrodynamic diameter of the silica/polymer network, where the hydrodynamic diameter portrays a peak shift as the CMC is acquired. Rheological measurements display a reduction in the apparent viscosity with surfactant concentration before increasing by 3.7–15% upon approaching the CMC. The viscoelastic properties display an optimum surfactant concentration, where a stress softening behavior occurs at higher frequencies, known as the Payne effect. As the volume fraction increases, the elastic region extends to lower strains and the onset of recoverable energy occurs below the CMC, while the viscous response exhibits a resistance to flow.