Effect of Addition of Sulfate Anions Containing Oxyethylene Moiety on Rheological Property of Smectite-water Dispersion

Abstract

The adsorption behavior of anionic surfactants [sodium α-alkylphenyl poly(oxyethylene)-ω-sulfate; R–C₆H₄–(OCH₂CH₂)_n–OSO₃Na, R = nonyl or octyl group, n = 9, 22 and 50] on smectite and their effect for rheological property of the smectite-water dispersion (2 wt% smectite) were investigated at 25 °C. The adsorbed amount of the sulfate anion was found to be increased with increasing the concentration of the sulfate anion and the number of oxyethylene unit (n value) in the sulfate anion, which was observed remarkable in alkaline solutions and not so in acid solutions. From the results, it was assumed that the sulfate anion is adsorbed on layer surface by the interaction with polyoxyethylene moiety in alkaline solutions and also on layer edge by the electrostatic interaction with sulfate group in acid solutions. In the measurement of rheological property, the apparent viscosity was decreased with increasing the adsorbed amount of the sulfate anion in alkaline solutions. In the case of addition of acid to the dispersion, the change in the apparent viscosity of the dispersion seems to be smaller than in the case of absence of the sulfate anion. Therefore, it was considered that the sulfate anion adsorbed on layer surface or layer edge depend on the dispersion pH prevents the association of smectite particles in the dispersion. Thus by the formation of the smectite sulfate anion composite, smectite became useful in weak acidic conditions and the change in rheological property of the smectite-water dispersion can be explained by the adsorption behavior of the sulfate anion to smectite.