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-liqui d interactions on the stability and structure formation of suspensions of hydrophobic and hydrophilic aerosil particles in the mixtures benz ene-n-heptane, methanol-benzene and 1-propanol-water. For the binary m ixtures, the Hamaker constants have been determined by optical dispers ion measurements over the entire composition range. The Hamaker consta nt of the adsorption layer, of composition different from that in the bulk, has been calculated for several mixture compositions on the basi s of the above results. Having the excess isotherms available enabled us to determine the adsorption layer thickness as a function of the mi xture composition. For interparticle attractive potentials, model calc ulations have been effected on the basis of the Vincent model. In the case of hydrophobic particles dispersed in benzene-n-heptane and metha nol-benzene mixtures, it was established that the change in the attrac tive potential was in accordance with the interactions obtained from r heological measurements. However, for silica particles dispersed in 1- propanol-water mixtures, the structure-forming and rheological propert ies of the dispersed system are determined by the alcohol-water struct ure, i.e. by propanol-water clusters.