INTERPARTICLE INTERACTIONS IN TITANIUM-DIOXIDE DISPERSIONS

Studies were performed to reveal how interparticle interactions in dis persions of titanium dioxide (rutile modification) depend on the natur e of the dispersion medium (water, isopropanol, and 1,4-dioxane). The influence of pH, addition of sodium sulfate, and adsorption of poly(me thacrylic acid) (the molecular mass of 120 x 10(3)) on these interacti ons in aqueous solutions was also studied. The number of primary parti cles in aggregates was determined from the data of sedimentation analy sis. It was shown that redispersion of the titanium dioxide powder to primary particles is never complete, and this process leads to the for mation of equilibrium aggregates, whose size depends on the nature of the dispersion medium and on the solid phase concentration. The titani um dioxide suspensions are unstable with respect to aggregation in wea kly acidic media near the isoelectric point. In contrast, the suspensi ons stable with respect to aggregation are formed in strongly acidic a nd alkaline media, but these suspensions become unstable upon the addi tion of electrolyte. The suspensions become stable upon adsorption of poly(methacrylic acid) on the titanium dioxide particles, and their st ability is retained upon the addition of electrolyte up to the concent ration of 0.01 mol/l, If one assumes that the adsorbed polyelectrolyte layers change the ion-electrostatic and dispersion components of the disjoining pressure, then the experimental results agree with the DLVO theory of the aggregation stability of lyophobic colloids.