Smectites as colloidal stabilizers of emulsions: II. Rheological properties of smectite-laden emulsions

Abstract

Oil-in-water emulsions were prepared by dispersing aqueous dispersions of several bentonites, montmorillonites, and hectorites (2% solid content) in paraffin oil which contained 100 mg/25 ml of a coemulsifier (alkyl polyglucoside, glycerol monostearate, lecithin, tetra- and deca(ethylene oxide) hexadecyl ethers). The colloidal stabilizers were sodium montmorillonite from Wyoming (USA), sodium bentonite from Kimolos (Greece), soda-activated bentonite from Milos (Greece) and Kimolos, also after decomposition of the carbonate. Three samples of synthetic hectorites (as synthesized, after washing, and after impregnation with sodium polyphosphate) were also used as colloidal stabilizers. The processing steps had strong effects on the rheological properties of the clay mineral dispersions. The rheological behavior of emulsions reflected these properties of the dispersions. Due to the presence of the dispersed oil droplets, the shear stresses of the emulsions were distinctly higher than the corresponding values of the dispersions and increased with the oil volume fraction. Their behavior changed from antithixotropic to thixotropic with increasing oil volume fraction. The storage modulus G′ of the emulsions with alkyl polyglucoside and glycerol monostearate showed no linear viscoelastic regions indicating the destructive character of the oscillation experiments even at the smallest deformation and the lowest frequencies. The structure of the emulsion was more stable in the presence of lecithin and ethylene oxide ethers and resisted to the shearing forces during the oscillation experiments as indicated by the observation of linear viscoelastic regions.