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|Título:||Shear-induced defect formation in a nonionic lamellar phase|
Miguel, M. G.
|Editora:||American Chemical Society|
|Resumo:||(2)H NMR experiments on a nonionic oriented lamellar phase demonstrate that shear flow induces structural defects in the lamellar structure. These substantial structural changes give rise to a transition from a viscous to a solidlike behavior; the elastic modulus of presheared samples was found to increase, reversibly, with the applied preshear rate. A similar behavior was found when step-cycling the temperature toward the layer-to-multilamellar-vesicle transition and back at constant shear rate. However, while shear rate controls the defect density, the temperature is found to control the defect rigidity. The lamellar phase exhibits a shear-thinning behavior under steady shear conditions, following the power law eta similar to gamma(n), with n approximate to -0.4. Both the shear thinning and the elastic behavior are in agreement with the available theoretical models. The observed shear-induced structural defects are reversible and can be regarded as a pretransition prior to the shear-induced formation of multilamellar vesicles.|
|Aparece nas colecções:||FCT2-Artigos (em revistas ou actas indexadas)|
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|Shear-Induced Defect Formation in a Nonionic Lamellar Phase.pdf||1,26 MB||Adobe PDF||Ver/Abrir Acesso Restrito. Solicitar cópia ao autor!|
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