Formation and characterization of soy bean oil/surfactant/NaCl aqueous solution microemulsions
M. A. Polizelli1; A.L Santos1; V.R.N. Telis3; G. O. Bonilla-Rodriguez2; E. Feitosa1
1UNESP, Departamento de Física, São José do Rio Preto – SP – Brasil.
2UNESP, Departamento de Química e Ciências Ambientais, São José do Rio Preto – SP – Brasil.
3UNESP, Departamento de Engenharia Ciências e Tecnologia de Alimentos, São José do Rio Preto – SP – Brasil.
Microemulsions (MEs) are homogeneous dispersions of water-in-oil (W/O) or oil-in-water (O/W) droplets stabilized by surfactants (emulsifiers). The MEs are formed spontaneously and exhibit typical physical-chemical properties, such as optical transparency and isotropy, low viscosity and thermodynamic stability.
This work aims to find a W/O ME single phase region in (pseudo)ternary phase diagrams of systems containing soy bean oil (SBO) and water or NaCl aqueous solution, as well as the anionic and zwiterionic surfactants bis (2-ethylexyl) sodium sulfosuccianate (AOT) and Phophatidil Choline (PC), theses systems have a possible utilization in foods. Rheology measurements were obtained to ME and pure SBO in order to characterize and compare the viscosity of the two system.
The phase diagrams were constructed by diluting a mixture of x (percent weight of surfactant) with y (percent weight of SBO. Microvolumes of water or NaCl aqueous solution were then added to surfactant:SBO mixtures following the x:y dilution lines in the ternary phase diagrams, and the samples observed by eyes and cross polaroids. Theses phase diagrams were constructed for the systems soybean oil (SBO)⁄surfactant⁄water, with AOT, PC and mixtures of these surfactants with ratios of AOT:PC 2:1, 1:1 and 1:2. The area of ME formation was shown to be dependent of the relative amount of surfactants and to pure surfactants there is no formation of ME and for the diagrams with mixture ratios of AOT:PC 2:1, 1:1 and 1:2 the areas of ME were 1.4, 2.1 and 1.4% of the whole phase diagram area, respectively. Pseudoternary phase diagrams were constructed for the systems with a ratio of AOT:PC 1:1 (which presented larger ME area) with a NaCl aqueous solution with 2, 5, 8, 11 and 15% (w/w). The area of ME formation increase with concentration of salt, and in the concentration of 11% reached the maxim area of ME formation. Rheological measurements were made using a Brookfield rotational rheometer, equipped with a cone and plate probe. The viscosity of the MEs with composition near to the SBO vertices, vary around 50 cP, values similar SBO viscosity. In larger concentrations of surfactant the viscosity of MEs increases in ten times this value. The relative viscosity increased with the water content, following a dilution line in the phase diagram, i.e., a constant surfactant:SBO percentage ratio. These behaviors confirm the existence of ordinary W/O ME droplets.
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