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|Type:||Artigo de periódico|
|Title:||Effects of a cosurfactant on the shear-dependent structures of systems composed of biocompatible ingredients|
da Cunha, RL
|Abstract:||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. (C) 2012 Elsevier B.V. All rights reserved.|
|Editor:||Elsevier Science Bv|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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