Solubilization of α-tocopherol and curcumin by polyoxyethylene alkyl ether surfactants: Effect of alkyl chain structure

•Ability of Brij micelles to solubilize guest molecules were investigated.•The solubilization within Brij micelles was affected by guest molecule type.•The nature of the alkyl chains of Brij affected the guest molecule solubilization.•Brij having the shortest alkyl chain showed the largest solubilization ability.•Guest molecule location depended on its type and alkyl chain nature of Brij. The effects of the structural characteristics of the alkyl chains of polyoxyethylene alkyl ether-type surfactants (Brij) on the solubilization of α-tocopherol and curcumin by surfactant micelles were investigated: Brij L23 (lauryl; C12:0); S20 (stearyl; C18:0); and Brij O20 (oleyl; C18:1). When α-tocopherol or curcumin were solubilized in Brij micelle solutions below their maximum solubilization concentrations (Cmax), the Brij L23 micelles exhibited the largest increase in dimensions due to the presence of the guest molecules. Above Cmax, excess α-tocopherol existed as microemulsion droplets whereas excess curcumin existed as insoluble crystals. Our results suggest that the guest molecules were preferentially located within the palisade layers of micelles, which can be attributed to the fact that they contained bother polar and non-polar moieties. These results may be important for the formulation of colloidal delivery systems to encapsulate and deliver oil-soluble vitamins and nutraceuticals.