SMALL-ANGLE X-RAY-SCATTERING OF COLLOIDAL AEROSIL PARTICLES IN BINARY-LIQUID MIXTURES

Hydrophilic and hydrophobic colloid SiO2 particles dispersed in benzen e-n-heptane mixtures were studied by small-angle X-ray scattering (SAX S) in an He atmosphere. The adsorption of the components, the rheologi cal properties and the optical density of the suspensions were also de termined. In mixtures of benzene and n-heptane, adhesion between the p articles decreased due to the positive adsorption of benzene, since, a ccording to results obtained by micro-calorimetry the heat of wetting increases in benzene-rich mixtures. According to SAXS measurements, th e difference between hydrophilic and hydrophobic particles is well cha racterized by the primary scattering intensities I-o. Correlation leng th and the course of the distance distribution function P(r), were cal culated from I(h), yield information on aggregation and on the stabili ty of the disperse system. The rheological flow curves reveal that in n-heptane there are strong adhesive interactions between both hydrophi lic and hydrophobic particles. The yield value tau(B) is characteristi c of interparticle interactions, and changes in parallel with the tail -end constant K-p and with the parameter of inhomogeneity. Aggregation is also demonstrated by the observation of the relative internal surf ace of the suspension changes with the composition of the mixture. (C) 1998 Elsevier Science B.V.