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Abstract
A biphasic solution containing an isotropic L1-phase and L α -phase (multilamellar vesicles) was illustrated in order to investigate the consequences of glycerol addition on the swelling behavior of L α -phase at different glycerol concentrations and temperature values. The multilamellar vesicles were prepared from mixing cationic surfactant cetyltrimethylammonium bromide (CTAB) and hydrophobic counterion sodium 3-hydroxynaphthalene 2-carboxylate (NaHNC) at the same molar ratio. Different techniques were used in order to investigate the swelling behavior of the L α -phase by establishing the phase diagram, observing the solutions via polarizing microscopy, and measuring different rheological parameters. A comparison study between the effect of glycerol addition and temperature on the swelling behavior was performed. By adding glycerol to water at 40%, the two-phase L1/L α region was swollen to a single L α phase and the solution became transparent at 40°C. On the other hand, the swelling of L α -phase was observed in water solvent at higher temperature values. The vesicles were with higher flexibility at low glycerol content and became rigid when the glycerol content was increased. In addition, the complex viscosity, η* followed the same increase-decrease in two conditions. In the first case, η* was varied with glycerol content at constant temperature and in the second case η* was varied with temperature at constant glycerol content. Such a result indicates that the rheological behavior is also influenced by the solvent properties. Furthermore, this study shows that with increasing glycerol content, the swelling in the L α phase was attributed with a decrease in the attraction energy between the vesicles. Ultimately, it has shown that it is possible to convert the two-phase L1/L α into a single L α phase by controlling some physical parameters of the medium as the static dielectric constant and the refractive index. The results obtained are expected to be useful in many different applications of surfactant solutions.
Acknowledgments
The author acknowledges Prof. Dr. Heinz Hoffmann for bringing the idea of using glycerol in these combinations and also for his useful notes and discussions. Prof. Dr. Grehard Platz and Dieter Gräbner are also acknowledged for their kind help in polarization microscopy measurements. Mr. Shabeer Sattar and Dr. Ayman Salim Ayesh helped to improve the quality of this article.