Thursday, March 19, 2009

Small-angle X-ray scattering of colloidal aerosil particles in binary liquid mixtures

Hydrophilic and hydrophobic colloid SiO2 particles dispersed in benzene-n-heptane mixtures were studied by small-angle X-ray scattering (SAXS) in an He atmosphere. The adsorption of the components, the rheological properties and the optical density of the suspensions were also determined. In mixtures of benzene and n-heptane, adhesion between the particles decreased due to the positive adsorption of benzene, since, according to results obtained by micro-calorimetry the heat of wetting increases in benzene-rich mixtures. According to SAXS measurements, the difference between hydrophilic and hydrophobic particles is well characterized by the primary scattering intensities I0. Correlation length and the course of the distance distribution function P(r), were calculated from I(h), yield information on aggregation and on the stability of the disperse system. The rheological flow curves reveal that in n-heptane there are strong adhesive interactions between both hydrophilic and hydrophobic particles. The yield value τB is characteristic of interparticle interactions, and changes in parallel with the tail-end constant KP and with the parameter of inhomogeneity. Aggregation is also demonstrated by the observation of the relative internal surface of the suspension changes with the composition of the mixture.

Author Keywords: Silica particles; Adsorption; Wetting; Rheology of suspensions; SAXS; Hydrophilic/hydrophobic surfaces

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