| 1. |
- dos Santos, Tiago, et al.
(författare)
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How does a non-ionic hydrophobically modified telechelic polymer interact with a non-ionic vesicle? Rheological aspects
- 2008
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 319:1-3, s. 173-179
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Konferensbidrag (refereegranskat)abstract
- The association between hydrophobically modified polyethylene glycol, HM-PEG, and non-ionic vesicles of tetraethylene glycol monododecyl ether, C12E4, was investigated. HM-PEG is in a triblock form, with an alkyl chain attached to each hydrophilic polymer-end. Such polymer structure is denoted as telechelic. The vesicle average radius was measured by self-diffusion measurements. The system exhibits both a monophasic gel and biphasic regions. The monophasic region was characterized from a theological point of view. We argue that the gel formation is due to the presence. of polymer crosslinks between different surfactant aggregates, once the polymer's hydrophobic moieties may adsorb into the vesicle bilayer. This association is strongly concentration dependent which is reflected in the monotonic increase of the storage modulus, relaxation time and shear viscosity with the addition of surfactant and/or polymer.
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| 2. |
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| 3. |
- Ferreira, Tiago, et al.
(författare)
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Segmental order parameters in a nonionic surfactant lamellar phase studied with 1H-13C solid-state NMR.
- 2008
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 10:39, s. 6033-6038
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Tidskriftsartikel (refereegranskat)abstract
- A lyotropic nonionic lamellar system composed of pentaethyleneglycol mono n-dodecyl ether and D(2)O was studied using natural abundance (13)C NMR under magic-angle spinning. Applying a two-dimensional recoupling method proposed by Dvinskikh (R-PDLF), (1)H-(13)C dipolar couplings were estimated over a range of temperatures (300-335 K), thus enabling analysis of structural changes in the liquid crystalline system. The results obtained are used to correlate the conformation and mobility of local sites in the surfactant molecule with overall changes in the lamellar structure.
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| 4. |
- Filippelli, Luigi, et al.
(författare)
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Metastability of Multi-Lamellar Vesicles in a Nonionic System
- 2009
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Ingår i: Molecular Crystals and Liquid Crystals. - : Informa UK Limited. - 1542-1406 .- 1543-5318 .- 1563-5287. ; 500, s. 166-181
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Konferensbidrag (refereegranskat)abstract
- Nuclear magnetic resonance spectroscopy and rheological analysis have been used to investigate the stability of mechanically induced tri-ethylene-glycol-mono-n-decyl-ether (C10E3)/deuterium oxide (D2O) multi-lamellar vesicles (MLVs) and the transition from MLVs to planar lamellae. It was found that MLVs prepared by vortex stirring, relax back to the lamellar phase in a few hours while the relaxation of the shear induced MLVs takes days. Pulsed gradient spin echo and water self-diffusion coefficient experiments, revealed that the MLVs texture, obtained by vortex stirring, is composed of large size structures. These data indicate that the kinetics of lamellar re-formation depend on the MLVs number density.
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| 5. |
- Medronho, Bruno, et al.
(författare)
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Shear-Induced Transitions between a Planar Lamellar Phase and Multilamellar Vesicles: Continuous versus Discontinuous Transformation.
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:13, s. 6480-6486
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Tidskriftsartikel (refereegranskat)abstract
- The shear-induced transitions between an oriented lamellar phase and shear-induced multilamellar vesicles (MLVs) in a nonionic surfactant system were studied by deuterium rheo-NMR spectroscopy as a function of time in start-up experiments at several temperatures and shear rates. By starting from an initial state of oriented lamellae and observing the transformation to the final steady state of MLVs and vice-versa, two different mechanisms were found, depending on the direction of the transition and the initial state. The transition is continuous when MLVs are formed, starting from the oriented lamellar phase. On the other hand, a discontinuous nucleation-and-growth process with a coexistence region is observed when transforming MLVs into an oriented lamellar phase.
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| 6. |
- Medronho, Bruno, et al.
(författare)
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Viscoelasticity of a nonionic lamellar phase
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:10, s. 5270-5274
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Tidskriftsartikel (refereegranskat)abstract
- The linear viscoelastic properties of a nonionic lamellar phase in C-orientation were studied as a function of temperature by small-amplitude oscillatory measurements in the frequency range 0.5-5 Hz. An almost solidlike elastic response was observed at all studied temperatures, from 42 to 20 degrees C. In this range, the elastic modulus was found to increase strongly with decreasing temperature. The elasticity is attributed to screw dislocations connecting layers in the stack, and the data thus suggest that the density of screw dislocations decreases with increasing temperature. The lamellar phase forms an "onion" texture when continuously sheared at lower temperatures. It is argued that a possible origin for the shear-induced "onion" texture is the instability of the screw dislocations in shear flow. By H-2 NMR experimentation, we also find the formation of a random mesh phase at lower temperatures. The presence of equilibrium bilayer perforations, however, does not correlate with the "onion" stability.
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