Effects of Surfactant Hydrophilicity on the Oil Solubilization and Rheological Behavior of a Nonionic Hexagonal Phase

Abstract

The effects of surfactant hydrophilicity on the phase behavior and rheology of a hexagonal phase (H 1 ) and related O/H 1 emulsions in a water/C 12 EO n /isohexadecane system (n = 7, 9) have been investigated. In this phase behavior study, a variety of surfactant aggregates (micellar, W m ; hexagonal, H 1 ; bicontinuous cubic, V 1 ; lamellar, L a ; inverse micellar, O m ) have been observed in water-C 12 EO n binary systems. The oil solubility of different surfactant aggregates was strongly affected by the surfactant hydrophilicity, i.e., surfactant aggregates in the C 12 EO 7 system could solubilize a larger amount of oil than those in the C 12 EO 9 system. It can be inferred that the surfactant with long hydrophilic head groups could be closely packed in the interface, leading to a reduction in the oil solubility in the micellar core due to the strong head group interaction. Interestingly, the rheology of the H 1 phase also exhibits behavior that is dependent on the surfactant hydrophilicity, i.e., high values of the elastic modulus G 0 and complex viscosity |g*| have been observed in the C 12 EO 9 system, possibly due to the strong neighboring head group interaction. Hexagon structure of the H 1 phase was calculated by using the Bohlin model. The viscosity of the O/H 1 emulsions decreases with increasing oil concentration, possibly due to the low volume fraction of the continuous phase (the H 1 phase).

Investigating the effect of a simplified perfume accord and dilution on the formation of mixed-surfactant microemulsions

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