Oscillatory testing of o/w emulsions containing mixed emulsifiers of the surfactant-long chain alcohol type: self-bodying action

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Abstract
Liquid paraffin-in-water emulsions stabilized by cationic (cetrimide) or non-ionic (cetomacrogol) surfactants and cetostearyl alcohol were examined at 25° in oscillatory mode, using the Weissenberg Rheogoniometer with parallel plates coupled to a digital transfer function analyser. Ternary systems, formed by dispersing the mixed emulsifiers in water, were similarly investigated. Each preparation was tested in the linear viscoelastic region, and fundamental rheological parameters, the storage modulus (G') and the real viscosity (ẽ') were derived as functions of frequency over the range 7.91 times 10−4to 25 Hz. All ternary systems behaved similarly with respect to frequency. As this increased, G' rose and ẽ' fell. These trends were related to the viscoelastic nature of the systems. Both mixed emulsifiers exhibited self-bodying mechanisms, so that emulsion consistency increased as the mixed emulsifier concentration rose. This was shown by increases in G' and ẽ' at each frequency. The shapes of the plots and other rheological properties were related to viscoelastic gel networks formed in the emulsion continuous phases. The ternary system parameters implied that emulsion networks were similar to ternary gels, that is, they formed by the interaction of long chain alcohol and aqueous surfactant solution. The oscillatory data were compared and correlated with creep data derived for similar ionic and non-ionic dispersed systems, previously described.