title: The influence of surfactant mixing ratio on nano-emulsion formation by the pit method.
abstract: The formation of O/W nano-emulsions by the PIT emulsification method in water/mixed nonionic surfactant/oil systems has been studied. The hydrophilic-lipophilic properties of the surfactant were varied by mixing polyoxyethylene 4-lauryl ether (C12E4) and polyoxyethylene 6-lauryl ether (C12E6). Emulsification was performed in samples with constant oil concentration (20 wt%) by fast cooling from the corresponding HLB temperature to 25 degrees C. Nano-emulsions with droplet radius 60-70 nm and 25-30 nm were obtained at total surfactant concentrations of 4 and 8 wt%, respectively. Moreover, droplet size remained practically unchanged, independent of the surfactant mixing ratio, X(C12E6). At 4 wt% surfactant concentration, the polydispersity and instability of nano-emulsions increased with the increase in X(C12E6). However, at 8 wt% surfactant concentration, nano-emulsions with low polydispersity and high stability were obtained in a wide range of surfactant mixing ratios. Phase behavior studies showed that at 4 wt% surfactant concentration, three-liquid phases (W+D+O) coexist at the starting emulsification temperature. Furthermore, the excess oil phase with respect to the microemulsion D-phase increases with the increase in X(C12E6), which could explain the increase in instability. At 8 wt% surfactant concentration, a microemulsion D-phase is present when emulsification starts. The low droplet size and polydispersity and higher stability of these nano-emulsions have been attributed, in addition to the increase in the surface or interfacial activity, to the spontaneous emulsification produced in the microemulsion D-phase.
authors.affiliation: Dept. Tecnologia de Tensioactius, Institut d'Investigacions Químiques i Ambientals de Barcelona, CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain.
authors.forename: Paqui
authors.initials: P
authors.lastname: Izquierdo
authors.forename: Jin
authors.initials: J
authors.lastname: Feng
authors.forename: Jordi
authors.initials: J
authors.lastname: Esquena
authors.forename: Tharward F
authors.initials: TF
authors.lastname: Tadros
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Dederen
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Garcia
authors.forename: Núria
authors.initials: N
authors.lastname: Azemar
authors.forename: Conxita
authors.initials: C
authors.lastname: Solans