| 1. |
- Behrens, Manja A, et al.
(author)
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Temperature-Induced Attractive Interactions of PEO-Containing Block Copolymer Micelles
- 2014
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:21, s. 6021-6029
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Journal article (peer-reviewed)abstract
- Interactions in a temperature sensitive-colloidal model system are investigated over a wide range of temperatures and concentrations to characterize the interparticle interactions within the system. This model system is composed of poly(ethylene oxide) end-capped with an octadecyl chain (C18E100), which by small-angle X-ray scattering (SAXS) have been shown to form spherical micelles in an aqueous salt solution. In the present study a 0.9 M NaF solution is used to shift the cloud point into the experimentally convenient temperature range. Densitometry and SAXS have shown no indication of specific interactions between the salt ions and the micelles. The spherical micelles are found to persist at elevated temperatures and a change in interparticle interaction is observed by viscometry and SAXS. The results are all consistent with the decreased solvent quality of water toward poly(ethylene oxide) with increasing temperature and it is seen that attractive interparticle interactions emerge in the vicinity of the cloud point.
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| 2. |
- Behrens, Manja, et al.
(author)
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The Shapes of Z-alpha(1)-Antitrypsin Polymers in Solution Support the C-Terminal Domain-Swap Mechanism of Polymerization
- 2014
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In: Biophysical Journal. - : Elsevier BV. - 1542-0086 .- 0006-3495. ; 107:8, s. 1905-1912
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Journal article (peer-reviewed)abstract
- Emphysema and liver cirrhosis can be caused by the Z mutation (Glu342Lys) in the serine protease inhibitor alpha 1-antitrypsin (alpha 1AT), which is found in more than 4% of the Northern European population. Homozygotes experience deficiency in the lung concomitantly with a massive accumulation of polymers within hepatocytes, causing their destruction. Recently, it was proposed that Z-alpha 1AT polymerizes by a C-terminal domain swap. In this study, small-angle x-ray scattering (SAXS) was used to characterize Z-alpha 1AT polymers in solution. The data show that the Z-alpha 1AT trimer, tetramer, and pentamer all form ring-like structures in strong support of a common domain-swap polymerization mechanism that can lead to self-terminating polymers.
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| 3. |
- Gentile, Luigi, et al.
(author)
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Dynamic Phase Diagram of a Nonionic Surfactant Lamellar Phase
- 2014
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In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:13, s. 3622-3629
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Journal article (peer-reviewed)abstract
- The dynamic phase diagram of triethylene glycol dodecyl ether (C12E3) in D2O was determined for 40, 50, and 60 wt % of surfactant. The shear flow effect on the nonionic lamellar phase was investigated as a function of temperature and concentration. The transition from planar lamellae (L-alpha)-to-multilamellar vesicles (MLVs) was characterized by means of rheology, rheo-small-angle neutron and light scattering. New insight into the nature of the transition region between L-alpha and the MLVs state is provided. A disorder-order transition was also observed by SANS. This is attributed to a transition from disordered MLVs to a close-packed array of MLV's with slightly higher order than before. Moreover flow instability was observed in the shear-thickening regime at 40 degrees C.
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| 4. |
- Gentile, Luigi, et al.
(author)
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Multilamellar Vesicle Formation from a Planar Lamellar Phase under Shear Flow
- 2014
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:28, s. 8316-8325
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Journal article (peer-reviewed)abstract
- The formation of multilamellar vesicles (MLVs) from the lamellar phase of nonionic surfactant system C12E5/D2O under shear flow is studied by time-resolved small angle neutron and light scattering during shear flow. A novel small angle neutron scattering sample environment enables the tracking of the lamellae alignment in the velocity-velocity gradient (1-2) plane during MLV formation, which was tracked independently using flow small angle light scattering commensurate with rheology. During the lamellar-to-multilamellar vesicle transition, the primary Bragg peak from the lamellar ordering was observed to tilt, and this gradually increased with time, leading to an anisotropic pattern with a primary axis oriented at similar to 25 degrees relative to the flow direction. This distorted pattern persists under flow after MLV formation. A critical strain and critical capillary number based on the MLV viscosity are demonstrated for MLV formation, which is shown to be robust for other systems as well. These novel measurements provide fundamentally new information about the flow orientation of lamellae in the plane of flow that cannot be anticipated from the large body of previous literature showing nearly isotropic orientation in the 2,3 and 1,3 planes of flow. These observations are consistent with models for buckling-induced MLV formation but suggest that the instability is three-dimensional, thereby identifying the mechanism of MLV formation in simple shear flow.
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