Microstructure characterization of Citrus sinensis essential oil surfactant systems

Full text: Surfactant systems (SS) can undergo into phase transition (PT) in aqueous solution (AS) and become more structured aggregates which can be used as controlled release systems. Citrus sinensis (L.) Osbeck essential oil (CSEO) presents larvicidal activity against Aedes aegypti and was used as oil phase of these SS. The aim of this study was obtain and characterize SS composed by procetyl (P), oleic acid (OA), CSEO and water (W) for Aedes aegypti larvae control. The formulations were prepared by magnetic stirring with different proportions of P:OA 2:1/CSEO/W. The samples were evaluated by Polarized light microscopy (PLM) and SAXS measurements were held at the Brazilian Synchrotron Light Laboratory (LNLS), bean line 1. The phase diagram showed four different phases: microemulsion (ME), liquid crystal (LC), emulsion and phase separation. Ten samples were chosen for characterization. Samples A1-A3 exhibited dark field typical of ME isotropic behavior. Malthese crosses and oil streaks were observed in samples A5-A10 and fan shape texture in sample C4, typical of anisotropic lamellar (L) and hexagonal (H) LC respectively. SAXS measurements confirmed PLM structures, with broad bands of low intensity for MEs, phase transition (A4) and for LLC structure, the positions of the peaks obey the relationship 1:2:3 (A5-A10) and 1:√3:√4 for HLC (C4). In conclusion, the SS were successfully obtained and the two techniques combined were essential for their microstructure characterization. (author)