The influence of dissolved gas on the interactions between surfaces of different hydrophobicity in aqueous media Part II. A spectroscopic study

Abstract

The aggregation of smooth hydrophobic and hydrophilic silica particles in the presence of different gases has been investigated at pH 5.6 and 10^-4 M KNO₃, using the attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR) technique. The rate of aggregation of methylated silica is enhanced in the presence of dissolved CO₂ but is unaffected by dissolved air, argon or nitrogen. The aggregation of hydrophilic and heat treated dehydroxylated silica is not influenced by any gas tested. For methylated silica, CO₂ adsorbs on to the surface as tiny microbubbles. These microbubbles decrease the colloid stability of the methylated silica particles, overcoming the electrostatic repulsion at pH 5.6 and 10^-4 M KNO₃. The results obtained are in broad agreement with our previous atomic force microscopy (AFM) investigation of interparticle forces and bubble–particle heterocoagulation studies.