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

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.