| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 594363 | Colloids and Surfaces A: Physicochemical and Engineering Aspects | 2012 | 10 Pages |
The phase transitions of systems composed of water, polyoxyethylene sorbitan monooleate (Tween 80), medium-chain triglycerides (MCTs) and ethanol were evaluated based on rheological properties using different proportions of MCT:ethanol (1:0, 2:1 and 1:2). Higher ethanol contents led to a broadened microemulsion (ME) region and a diminished liquid crystalline (LC) region in the phase diagram and resulted in the formation of systems with smaller particle sizes, lower viscosities and less shear-thinning. Different systems were obtained from the water titration of an initial mixture of 70% (w/w) surfactant and 30% (w/w) oil + ethanol. At low water contents, Newtonian W/O MEs were produced. At intermediate water contents, LC phases were observed, including viscous and gel-like structures with viscoelastic properties and complex rheology (shear-thinning, Bingham plastic or Herschel–Buckley behaviour). In addition, these samples exhibited time-dependent behaviours, showing thixotropy in systems rich in amphiphilic and nonpolar components and anti-thixotropy in systems with a prevalence of polar (ethanol and water) components. According to oscillatory measurements, cubic phases were most likely formed at 40% (w/w) water in systems with low (or an absence of) ethanol. At higher water contents (>50%, w/w), O/W milk-like emulsions were produced in systems with low ethanol contents, whereas O/W MEs were produced in the system with a high ethanol content. O/W MEs exhibited larger droplet sizes and lower viscosities than W/O MEs. The different structures depended strongly on the system composition, which enables the production of textures with potential applications in the food, cosmetic and pharmaceutical industries.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Structural changes were effectively identified by different rheological techniques. ► Ethanol increased microemulsion region and produced systems less shear-thinning and structured. ► Liquid crystalline phase showed complex rheology under small and high deformation. ► Thixotropic behaviour was observed in systems with prevailing nonpolar or amphiphilic components. ► Systems rich in polar components (water and ethanol) showed anti-thixotropic behaviour.
