The effect of particle size distribution on the rheology of an industrial suspension

The viscosity of a proprietary dental composite material, consisting of suspensions of crushed glass in a polymeric liquid of a 50/50 w/w urethane dimethacrylate and triethylene glycol dimethacrylate mixture has been measured using a tube viscometer. Narrow-sized fine (ultimate particle size of 0.2 μm, which agglomerate to form particles with a mean diameter of 0.05 μm), medium (d50= 1.7 μm) and coarse (25.5 μm) particle fractions were used as well as bimodal and trimodal mixtures. Total solids concentrations from 17% to 76(77)% by volume were covered. The results were analysed using extensions of the Farris theory for mixtures and reduced to the viscosity functions, hi (ϕi), for the three monomodal fractions. They were fitted to the Mooney, Krieger-Dougherty or the three-parameter Cheng equation. The effect of particle size distribution on the Krieger-Dougherty parameters is discussed. The viscosity functions summarize the experimental results and allow the viscosities of bimodal and trimodal mixtures not measured to be predicted. The use of the predictions for the formulation of the dental material is discussed. The methodology described can be used in the design of other suspension products.