| 1. |
- Burrows, Hugh D., et al.
(författare)
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Aqueous Solution Behavior of Anionic Fluorene-co-thiophene-Based Conjugated Polyelectrolytes
- 2009
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 1:4, s. 864-874
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Forskningsöversikt (refereegranskat)abstract
- Two anionic fluorene-thiophene alternating copolymers, poly[9,9-bis(4-sulfonylbutoxyphenyl)fluorene-2,7-diyl-2,5-thienylene] (PBS-PFT) and poly [9,9-bis(4-sulfonylbutoxyphenyl)fluorene-2,7-diyl-2,2'-bithiophene-5,5'- diyl] (PBS-PF2T), have been synthesized and their solution behaviors in water studied by UV-vis absorption spectroscopy, fluorescence, and electrical conductivity and compared with that of the previously studied conjugated polyelectrolyte (CPE) poly[9,9-bis(4-sulfonylbutoxyphenyl)fluorene-2,7-diyl-1,4-phenylene] (PBS-PFP). These conjugated polymers do not form solutions at the molecular level in water but instead form clusters. information on the structure of these clusters for PBS-PF2T comes from small-angle X-ray and neutron scattering. The relative ease of dispersing the copolymers in water increases with an increase in the number Of thiophene rings in these alternating copolymers. Semiempirical calculations on the structure suggest that this results from bending of the chains and increased conformational flexibility, decreasing interchain interactions. These CPEs can be dissolved in water at the molecular level using the nonionic surfactants n-dodecylpentaoxyethylene glycol ether (C12E5) or Triton X-100 to obtain systems with increased photoluminescence quantum yield and increased electrical conductivity that can be solution-processed for potential applications as components of sensory or optoelectronic devices.
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| 2. |
- Bastardo Zambrano, Luis Alejandro, et al.
(författare)
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Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
- 2007
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 312, s. 21-33
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Tidskriftsartikel (refereegranskat)abstract
- A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO45 MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 Å. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO45 MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.
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| 3. |
- Raj, Akanksha, et al.
(författare)
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Lubrication synergy : Mixture of hyaluronan and dipalmitoylphosphatidylcholine (DPPC) vesicles
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 488, s. 225-233
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Tidskriftsartikel (refereegranskat)abstract
- Phospholipids and hyaluronan have been implied to fulfil important roles in synovial joint lubrication. Since both components are present in synovial fluid, self-assembly structures formed by them should also be present. We demonstrate by small angle X-ray scattering that hyaluronan associates with the outer shell of dipalmitoylphophatidylcholine (DPPC) vesicles in bulk solution. Further, we follow adsorption to silica from mixed hyaluronan/DPPC vesicle solution by Quartz Crystal Microbalance with Dissipation measurements. Atomic Force Microscope imaging visualises the adsorbed layer structure consisting of non-homogeneous phospholipid bilayer with hyaluronan/DPPC aggregates on top. The presence of these aggregates generates a long-range repulsive surface force as two such surfaces are brought together. However, the aggregates are easily deformed, partly rearranged into multilayer structures and partly removed from between the surfaces under high loads. These layers offer very low friction coefficient (<0.01), high load bearing capacity (≈23 MPa), and self-healing ability. Surface bound DPPC/hyaluronan aggregates provide a means for accumulation of lubricating DPPC molecules on sliding surfaces.
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| 4. |
- Wieland, D. C. Florian, et al.
(författare)
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Studying solutions at high shear rates : A dedicated microfluidics setup
- 2016
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography. - 0909-0495 .- 1600-5775. ; 23:2, s. 480-486
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Tidskriftsartikel (refereegranskat)abstract
- The development of a dedicated small-angle X-ray scattering setup for the investigation of complex fluids at different controlled shear conditions is reported. The setup utilizes a microfluidics chip with a narrowing channel. As a consequence, a shear gradient is generated within the channel and the effect of shear rate on structure and interactions is mapped spatially. In a first experiment small-angle X-ray scattering is utilized to investigate highly concentrated protein solutions up to a shear rate of 300000 s-1. These data demonstrate that equilibrium clusters of lysozyme are destabilized at high shear rates.
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| 5. |
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| 6. |
- Bergström, L. Magnus, et al.
(författare)
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Geometrical Shape of Micelles Formed by Cationic Dimeric Surfactants Determined with Small-Angle Neutron Scattering
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:25, s. 9311-9321
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Tidskriftsartikel (refereegranskat)abstract
- The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C12H25N(CH3)(2)(CH2)(5)N(CH3)(2)C12H25 (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 124-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 <= s <= 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 <= s <= 12.
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| 7. |
- Bergström, L. Magnus, et al.
(författare)
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The growth of micelles, and the transition to bilayers, in mixtures of a single-chain and a double-chain cationic surfactant investigated with small-angle neutron scattering
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 7:22, s. 10935-10944
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembly in aqueous mixtures of a single-chain (DTAB) and a double-chain cationic surfactant (DDAB) has been investigated with small-angle neutron scattering (SANS). Small oblate spheroidal micelles formed by DTAB grow with respect to width and length to form mixed ellipsoidal tablet-shaped micelles as an increasing fraction of DDAB is admixed into the micelles. The growth behaviour of the micelles is rationalized from the general micelle model in terms of three bending elasticity constants spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant ((k(c)) over bar kc). It is found that micelles grow with respect to width, mainly as a result of decreasing k(c)H(0), and in the length direction as a result of decreasing k(c). The micelles are still rather small, i.e. about 140 angstrom in length, as an abrupt transition to large bilayer aggregates is observed. The micelle-to-bilayer transition is induced by changes in aggregate composition and is observed to occur at a mole fraction of DDAB equal to about x = 0.48 in D2O, which is a significantly higher value than previously observed for the same system in H2O (x = 0.41). An abrupt micelle-to-bilayer transition is in agreement with predictions from the general micelle model, according to which an abrupt transition from micelles to bilayers is expected to occur at xi H-0 = 1/4, where x is the thickness of the self-assembled interface, and we may conclude that H-0(D2O) > H-0(H2O) for the system DDAB/DTAB in absence of added salt. Samples with bilayers are found to be composed of bilayer disks coexisting with vesicles. Disks are found to always predominate over vesicles with mass fractions about 70-90% disks and 10-30% vesicles. Micelles, disks and vesicles are observed to coexist in a few samples close to the micelle-to-bilayer transition.
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| 8. |
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| 9. |
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| 10. |
- Meister, Anette, et al.
(författare)
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Formation of square lamellae by self-assembly of long-chain bolaphospholipids in water
- 2010
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:6, s. 1317-1324
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembly process of the symmetric single-chain polymethylene-1,omega-bis(phosphocholine) (PC-C34-PC) with a chain length of 34 carbon atoms and two polar phosphocholine headgroups when put into water is exclusively driven by hydrophobic interactions of the long alkyl chains. This process leads to the formation of a dense network of helical nanofibers and the formation of a hydrogel (Meister et al. J. Phys. Chem. B, 2008, 112, 4506). In contrast, the single-chain bolalipids tetra-and hexatriacontane-1,omega-diyl-bis[2-(dimethylammonio)ethylphosphate] (Me2PE-Cn-Me2PE, n = 34, 36) and the partly deuterated analogue Me2PE-C11-(CD2)12-C11-Me2PE (dMe(2)PE-C34-Me2PE) form a different type of stable aggregate. In a first step, the self-assembly of these long-chain bolalipids in water at room temperature leads to the formation of a dense network of nanofibers which eventually form a hydrogel. Within one day, the nanofibers transform into square lamellae that grow up to an edge length of about 100 nm. Nanofibers are linked to one or two (opposite) corners of the squares leading to the appearance of a kite-like structure. After one week, all fibers have been transformed into square lamellae which are apparently stacked and form a gel cake. Within several weeks, a more compact cake is formed by syneresis, i.e. the expulsion of water.
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