A rheological investigation of the self-assembly and adsorption behavior of a surfactant salt.
The properties of a surfactant salt obtained by neutralizing oleic acid with an ethoxylated stearylamine were determined in blends of water and propylene glycol. The adsorption of this surfactant salt onto the surface of a commercial TiO(2) dispersed in blends of water and propylene glycol was studied using a rheometer. At low propylene glycol content the dispersions exhibited Newtonian behavior, but became shear-thinning fluids with high viscosity at propylene glycol contents above a critical concentration. The observed behavior is consistent with a model involving a surfactant bilayer below the critical point, moving to a monolayer above the critical point. The high viscosity above the critical point is generated by reversible flocculation via hydrophobic forces. The viscosity of the dispersion flocculated by the hydrophobic forces was found to be much higher than that caused by flocculation via van der Waals forces in the absence of surfactant. Changing both the total concentration of the surfactant in the dispersion and the dispersion temperature resulted in a reversible transition between the bilayer and the monolayer. Although the surfactant was always above its critical micelle concentration (CMC) the amount on the particle surface varied appreciably with both propylene glycol and surfactant concentration.
Liang
Genhai G
GG
Key Centre for Polymer Colloids, School of Chemistry, University of Sydney, NSW 2006, Australia.
Hawkett
Brian S
BS
Tanner
Roger I
RI
D000327:Adsorption; D000588:Amines / Q000737:chemistry; D008823:Micelles; D019301:Oleic Acid / Q000737:chemistry; D010316:Particle Size; D019946:Propylene Glycol / Q000737:chemistry; D012212:Rheology; D012492:Salts / Q000737:chemistry; D012995:Solubility; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry
D000588:Amines; D008823:Micelles; D012492:Salts; D013501:Surface-Active Agents; D014867:Water; C009495:titanium dioxide; D019301:Oleic Acid; D019946:Propylene Glycol; D014025:Titanium; C009317:stearylamine