THE PROPERTIES OF THE ADSORPTION LAYER AND THE STABILITY OF AEROSIL DISPERSIONS IN BINARY LIQUIDS

From a knowledge of the adsorption, immersion and wetting properties, we have examined the influence of particle-particle and particle-liquid interactions on the stability and structure formation of suspensions of hydrophobic and hydrophilic aerosil particles in the mixtures benzene-n-heptane, methanol-benzene and 1-propanol-water. For the binary mixtures, the Hamaker constants have been determined by optical dispersion measurements over the entire composition range. The Hamaker constant of the adsorption layer, of composition different from that in the bulk, has been calculated for several mixture compositions on the basis of the above results. Having the excess isotherms available enabled us to determine the adsorption layer thickness as a function of the mixture composition. For interparticle attractive potentials, model calculations have been effected on the basis of the Vincent model. In the case of hydrophobic particles dispersed in benzene-n-heptane and methanol-benzene mixtures, it was established that the change in the attractive potential was in accordance with the interactions obtained from rheological measurements. However, for silica particles dispersed in 1-propanol-water mixtures, the structure-forming and rheological properties of the dispersed system are determined by the alcohol-water structure, i.e. by propanol-water clusters.