Effect of Alkyl Sulfate on the Phase Behavior of Microemulsions Stabilized with Monoacylglycerols

Abstract

In this study the effect of an anionic surfactant (sodium dodecyl sulfate SDS) and oils (hydrocarbons: C12-C16) on the formation and phase behavior of the systems of oil/monoacylglycerols (MAG):SDS/propylene glycol/water has been investigated. The effects of the surfactant mixture on the phase behavior and the concentration of water or oil in the systems were studied at three temperatures (50, 55, 60°C). Electrical conductivity measurement, FT-IR spectroscopy and differential scanning calorimetry methods were applied to determine the structure and type of the microemulsions formed. The dimension of microemulsion droplets was characterized by dynamic light scattering. It has been stated that the concentration of SDS has a strong influence on the shape and extent of the microemulsion areas. Addition of an ionic surfactant to the mixture with MAG promotes an increase in the area of microemulsion formation in the phase diagrams, and these areas of the isotropic region change with the temperature. It was shown that the presence in the systems of a surfactant more hydrophilic than MAG caused an increase in water content in the microemulsions. It was found that, depending on temperature and concentration of the surfactant mixture, it was possible to obtain a W/O type microemulsion with a dispersed particles size distribution ranging from 20 to 50 nm and containing about 17-38% water in the system. Among different alkanes (from C12 to C16), hexadecane embedded microemulsions showed a maximum water solubilization capacity. Keywords Microemulsions Á Monoacylglycerols Á Sodium dodecyl sulfate Á FT-IR Á DSC Á DLS Abbreviations FTIR Fourier transform infrared MAG Monoacylglycerols ME Microemulsions MLS Multiple light scattering PG Propylene glycol (1,2-propanediol) SDS Sodium dodecyl sulfate

Structure of Microemulsion Formulated with Monoacylglycerols in the Presence of Polyols and Ethanol

“…The research shows that ethanol strongly affects the microstructure transition, because, as it was shown in our previous work [ 18 ], the same systems but without ethyl alcohol did not present a maximum, because they were probably already percolated, even with 1 % of the aqueous phase. This phenomenon can be explained by the lower concentrations of water added to the system when the aqueous phase was a solution of ethanol and water (electrolyte in water).…”

“…Figure 4 b–d shows a plot of d(log κ)/d( W ) as a function of the water content for the systems presented in Fig. 3 a, depending on the EtOH concentrations (a model for the explanation of the behavior of the slope d(log κ)/d( W ) as a function of the water fraction was initially shown in our previous work [ 18 ]). Occurrence of the changes (the maximum) have been attributed to the occurrence of a percolation transition.…”

“…The recognition of the phase behavior and water solubilization capacity in the model system is expected to play a key role in producing ME as delivery systems, particularly with nonionic surfactants. In our previews study [ 18 ], we obtained four component systems based on MAG, that are homogeneous waxy solids at room temperature and, therefore they can immobilize, protect, inactivate, or slow down the activities of solubilized water-soluble matter during storage. The solid system will liquefy and convert or restore spontaneously into ME upon heating.…”

Environmentally Friendly Nonionic Surfactants Derived from Tannic Acid: Synthesis, Characterization and Surface Activity

“…Figure 5 represents the effect of the hydrophobic chain length of the synthesized nonionic surfactants on their CMC values when the ethylene glycol content kept constant. The general observation from this figure is the relatively low CMC values (1.22, 1.01 and 0.78 mM) compared to the CMC values of the conventional nonionic surfactants (octyl polyglucoside and/or dodecyl polyglucoside: 17.12 and 2.97 mM, respectively) [20,21]. It is also clear that the dodecyl derivatives (TN 15 D, TN 25 D and TN 50 D) have high CMC values compared to the other members in the prepared surfactants at 25°C.…”

Water Solubilization Using Nonionic Surfactants from Renewable Sources in Microemulsion Systems

“…Our systems (MAG, MAG + 10% CEO 20 and MAG + 20% CEO 20 ) did not present a maximum because they were probably already percolated, even with 1% of the aqueous phase. A model for the explanation of the behavior of the slope dlog κ/dW as a function of the water fraction was initially shown in our previous work [ 39 ]. The ethylene oxide moieties of the head group of the monomeric surfactant may already be associated with the polyol (cosurfactant) in the absence of water [ 40 ].…”