Foaming and gas holdup of esterified nanoparticle dispersions in the presence of sodium chloride

• Wetted hydrophobised silica nanoparticles increase the gas holdup of aqueous NaCl solutions.
• The addition of NaCl from 10−5 to 10−3 M caused a decrease in the gas holdup.
• Foaming of the colloidal dispersions improved when coagulated.
• The use of co-solvent (acetone) affects foaming if not properly removed.

The topic of particle-stabilised foams is relevant in many industrial applications such as the food industry, cosmetic, and mineral processing. This study is concerned with the influence of solid nanoparticles on the froth stability and gas holdup of aqueous solutions of sodium chloride. Silica nanoparticles with a nominal size of 300 nm were treated by esterification with 1-octanol to achieve intermediate hydrophobicity. Pneumatic foams were generated by passing nitrogen gas through a porous disc into the solutions. The results showed that increases in the concentration of nanoparticles in the colloidal dispersions caused slight increases in the gas holdup and had no significant effect on the foaminess of aqueous dispersions in the concentration range 0–6 wt%. Sodium chloride in sufficient amount to coagulate the particles significantly improved both gas holdup and foaminess. Electrolytes reduce the energy barrier that has to be overcome for the adsorption of particles to an interface and increase the hydrophobicity of the particles. As well, coagulated particulates have greater capture efficiency and hinder drainage in the froth, which could explain the improved foaminess in the present study. Additional experiments were performed to determine the effect of the composition of the continuous phase on the foaming properties. This was essential due to the use of a co-solvent to disperse the nanoparticles, which was shown to impact the foaminess of the dispersion if not removed adequately.

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