| 1. |
- Thompson, Katherine C., et al.
(författare)
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Degradation and Rearrangement of a Lung Surfactant Lipid at the Air-Water Interface during Exposure to the Pollutant Gas Ozone
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:14, s. 4594-4602
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Tidskriftsartikel (refereegranskat)abstract
- The presence of unsaturated lipids in lung surfactant is important for proper respiratory function. In this work, we have used neutron reflection and surface pressure measurements to study the reaction of the ubiquitous pollutant gas-phase ozone, 03, with pure and mixed phospholipid monolayers at the air-water interface. The results reveal that the reaction of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, with ozone leads to the rapid loss of the terminal C9 portion of the oleoyl strand of POPC from the air-water interface. The loss of the C9 portion from the interface is accompanied by an increase in the surface pressure (decrease in surface tension) of the film at the air-water interface. The results suggest that the portion of the oxidized oleoyl strand that is still attached to the lipid headgroup rapidly reverses its orientation and penetrates the air-water interface alongside the original headgroup, thus increasing the surface pressure. The reaction of POPC with ozone also leads to a loss of material from the palmitoyl strand, but the loss of palmitoyl material occurs after the loss of the terminal C9 portion from the oleoyl strand of the molecule, suggesting that the palmitoyl material is lost in a secondary reaction step. Further experiments studying the reaction of mixed monolayers composed of unsaturated lipid POPC and saturated lipid dipalmitoyl-sn-glycero-3-phosphocholine, DPPC, revealed that no loss of DPPC from the air-water interface occurs, eliminating the possibility that a reactive species such as an OH radical is formed and is able to attack nearby lipid chains. The reaction of ozone with the mixed films does cause a significant change in the surface pressure of the air-water interface. Thus, the reaction of unsaturated lipids in lung surfactant changes and impairs the physical properties of the film at the air-water interface.
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| 2. |
- Thompson, Katherine C., et al.
(författare)
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Reaction of a Phospholipid Monolayer with Gas-Phase Ozone at the Air-Water Interface : Measurement of Surface Excess and Surface Pressure in Real Time
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:22, s. 17295-17303
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Tidskriftsartikel (refereegranskat)abstract
- The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoy1-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known shout the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface. suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of H-1-POPC on D2O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air water interface leading to the formation of OH radicals. the highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation or oxidized lipids with shorter alkyl tails.
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| 3. |
- Ainalem, Marie-Louise, et al.
(författare)
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On the Ability of PAMAM Dendrimers and Dendrimer/DNA Aggregates To Penetrate POPC Model Biomembranes
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:21, s. 7229-7244
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Tidskriftsartikel (refereegranskat)abstract
- Poly(amido amine) (PAMAM) dendrimers have previously been shown, as cationic condensing agents of DNA, to have high potential for nonviral gene delivery. This study addresses two key issues for gene delivery: the interaction of the biomembrane with (i) the condensing agent (the cationic PAMAM dendrimer) and (ii) the corresponding dendrimer/DNA aggregate. Using in situ null ellipsometry and neutron reflection, parallel experiments were carried out involving dendrimers or generations 2 (G2), 4 (G4), and 6 (G6). The study demonstrates that free dendrimers of all three generations were able to traverse supported palmitoyloleoylphosphatidylcholine (POPC) bilayers deposited on silica surfaces. The model biomembranes were elevated front the solid surfaces upon dendrimer penetration, which offers a promising new way to generate more realistic model biomembranes where the contact with the supporting surface is reduced and where aqueous cavities are present beneath the bilayer. The largest dendrimer (GO) induced partial bilayer destruction directly upon penetration, whereas the smaller dendrimers (G2 and G4) leave the bilayer intact, so we propose that lower generation dendrimers have greater potential as transfection mediators. In addition to the experimental observations, coarse-grained simulations on the interaction between generation 3 (03) dendrimers and POPC bilayers were performed in the absence and presence of a bilayer-supporting negatively charged surface that emulates the support. The simulations demonstrate that G3 is transported across free-standing POPC bilayers by direct penetration and not by endocytosis. The penetrability was, however, reduced in the presence of a surface, indicating that the membrane transport observed experimentally was not driven solely by the surface. The experimental reflection techniques were also applied to dendrimer/DNA aggregates of charge ratio = 0.5, and while G2/DNA and G4/DNA aggregates interact with POPC bilayers. G6/DNA displays no such interaction. These results indicate that, in contrast to free dendrimer molecules, dendrimer/DNA aggregates of low charge ratios are not able to traverse a membrane by direct penetration.
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| 4. |
- Berts, Ida, et al.
(författare)
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Polymeric Smart Coating Strategy for Titanium Implants
- 2014
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Ingår i: Advanced Engineering Materials. - : Wiley. - 1438-1656 .- 1527-2648. ; 16:11, s. 1340-1350
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Tidskriftsartikel (refereegranskat)abstract
- Hyaluronan based hydrogel coatings can mimic extracellular matrix components and incorporate growth factors that can be released during a progressive degradation while new tissue regenerates. This paper describes a structural characterization of a hydrogel coating made of modified hyaluronan polymers and how these coatings interact with bone morphogenetic protein-2 (BMP-2). Quartz crystal microbalance and neutron reflectivity measurements were used for in-situ, real-time measurements of the adsorption properties of polymers and proteins on smooth titanium oxide surfaces that mimic implant products in orthopedics. The adsorption of BMP-2 on a bare titanium oxide surface is compared to that on titanium oxide coated with different chemically modified hyaluronan, the most important being hyaluronan with bisphosphonate groups (HA-BP). The subsequent release of the BMP-2 from these hydrogel coatings could be triggered by calcium ions. The amount of adsorbed protein on the surfaces as well as the amount of released protein both depend on the type of hyaluronan coating. We conclude that HA-BP coated titanium oxide surfaces provide an excellent material for growth factor delivery in-vivo.
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| 5. |
- Berts, Ida, 1984-
(författare)
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Relating the Bulk and Interface Structure of Hyaluronan to Physical Properties of Future Biomaterials
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation describes a structural investigation of hyaluronan (HA) with neutron scattering techniques. HA is a natural biopolymer and one of the major components of the extracellular matrix, synovial fluid, and vitreous humor. It is used in several biomedical applications like tissue engineering, drug delivery, and treatment of osteoarthritis. Although HA is extensively studied, very little is known about its three-dimensional conformation and how it interacts with ions and other molecules. The study aims to understand the bulk structure of a cross-linked HA hydrogel, as well as the conformational arrangement of HA at solid-liquid interfaces. In addition, the structural changes of HA are investigated by simulation of physiological environments, such as changes in ions, interactions with nanoparticles, and proteins etc. Small-angle neutron scattering and neutron reflectivity are the two main techniques applied to investigate the nanostructure of hyaluronan in its original, hydrated state.The present study on hydrogels shows that they possess inhomogeneous structures best described with two correlation lengths, one of the order of a few nanometers and the other in the order of few hundred nanometers. These gels are made up of dense polymer-rich clusters linked to each other. The polymer concentration and mixing governs the connectivity between these clusters, which in turn determines the viscoelastic properties of the gels. Surface-tethered HA at a solid-liquid interface is best described with a smooth varying density profile. The shape of this profile depends on the immobilization chemistry, the deposition protocol, and the ionic interactions. HA could be suitably modified to enhance adherence to metal surfaces, as well as incorporation of proteins like growth factors with tunable release properties. This could be exploited for surface coating of implants with bioactive molecules. The knowledge gained from this work would significantly help to develop future biomaterials and surface coatings of implants and biomedical devices.
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| 6. |
- Berts, Ida, et al.
(författare)
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Structure of polymer and particle aggregates in hydrogel composites
- 2013
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Ingår i: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 51:6, s. 421-429
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the structure of a biomaterial is usually vital to control its function. This article provides a structural characterization of a hyaluronan scaffold that has demonstrated good biocompatibility and is used to induce bone regeneration. Hyaluronan hydrogels are appealing materials that can function as a matrix to incorporate both organic and inorganic substances to enhance tissue growth. Because of the intrinsic properties of this swollen matrix, one needs a very sensitive technique that can be applied in situ to determine the organization of the polymers in a gel. Small-angle neutron scattering is used to determine the characteristics of the inhomogeneous structure of the hydrogel both with and without added particles. The results are interpreted using models of structure with two length scales that are beyond the traditional picture of homogeneous gels. The observed structure and the dimensions can explain the previously reported rheological properties of gels containing different amount of polymers. Hydroxyapatite nanoparticles added to the gel are frozen in the gel matrix. We are able to determine the distribution and shape of these particles as they aggregate around the polymer chains. We have also concluded, in this case, that the particle structure is concentration independent. Information about the nanostructure for an applicable biomaterial guides the formulation, preparation, and use that should lead to further understanding of its exploitation.
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| 7. |
- Berts, Ida, et al.
(författare)
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Tuning the density profile of surface-grafted hyaluronan and the effect of counter-ions
- 2013
-
Ingår i: European Physical Journal E. - : Springer Science and Business Media LLC. - 1292-8941 .- 1292-895X. ; 36:7, s. 70-
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Tidskriftsartikel (refereegranskat)abstract
- The present paper investigates the structure and composition of grafted sodium hyaluronanat a solid-liquid interface using neutron reflection. The solvated polymer at the surface could be described with a density profile that decays exponentially towards the bulk solution. The density profileof the polymer varied depending on the deposition protocol. A single-stage deposition resulted in denser polymer layers, while layers created with a two-stage deposition process were more diffuse and had an overall lower density. Despite the diffuse density profile, two-stage deposition leads to a highersurface excess. Addition of calcium ions causes a strong collapse of the sodium hyaluronan chains, increasing the polymer density near the surface. This effect is more pronounced on the sample prepared by two-stage deposition due to the initial less dense profile. This study provides an understanding at a molecular level of how surface functionalization alters the structure and howsurface layers respond to changes in calcium ions in the solvent.
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| 8. |
- Hellsing, Maja S., 1975-
(författare)
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Adsorption and Ordering of Surface Active Molecules and Particles at Solid Interfaces and in the Bulk
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Factors that influence the process of adsorption and order of dilute and concentrated systems of molecules and particles are explored in this thesis. The results are based largely on neutron scattering techniques. Study of the adsorption from dilute solutions of a common surfactant, AOT (sodium bis (2-ethylhexyl) sulfosuccinate), at a solid/liquid interface showed that AOT molecules adsorbed to the interface in a bilayer structure, with the hydrocarbon tails at maximum packing density even at very low concentrations. At higher AOT concentrations, a stack of fluctuating layers each separated by large amounts of water next to the dense bilayer was seen. The driving force for adsorption is dominated by self-assembly of AOT. It was found that an oriented lamellar phase wets the interface below the bulk concentration for formation of this phase.Proteins can be viewed as polymeric surfactants. The adsorption of proteins from seeds of the Moringa oleifera tree to a silicon oxide surface was studied to elucidate the mechanism of the protein as a flocculent in water treatment processes. The protein was found to adsorb at the interface as dense layers with a thickness suggestive of co-adsorption rather than single isolated molecules. The strong adsorption and tendency to associate in solution suggest mechanisms for flocculating particulate impurities in water.As with surfactants, dispersions of colloidal particles can assemble in regular structures by self-assembly. Polystyrene latex particles were studied and could form large three-dimensional crystals of about 1×1 cm2 in a 2 mm path cell. The diffraction pattern indicated a close packed structure with the 110 axis perpendicular to the container wall. The crystal was well-aligned and oriented by the direction of flow. At the solid interface large two-dimensional domains of about 20 cm2 of highly oriented particles were formed. The particle-particle separation at the surface and in the bulk was determined by the charge repulsion of the particles.
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| 9. |
- Hellsing, Maja S., et al.
(författare)
-
Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
- 2012
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:22, s. 221601-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the formation of large two-dimensional domains (about 20 cm2) of oriented and ordered structures of polystyrene particles dispersed in water at a solid/liquid interface. Gentle flow of the dispersed sample into the holder at a shear strain rate of about 0.1 s−1 caused particles at the air/latex meniscus to self-assemble in a regular structure on both solid silica or alumina surfaces. Scattering experiments show that the particle separation at the surface was the same as in the bulk and determined by repulsion arising from the charges on the particles. Close-packed planes formed parallel to the interface.
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| 10. |
- Hellsing, Maja S., et al.
(författare)
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Effect of Concentration and Addition of Ions on the Adsorption of Aerosol-OT to Sapphire
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:18, s. 14567-14573
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol-OT (sodium bis 2-ethylhexyl sulfosuccinate or NaAOT) adsorbs to hydrophilic sapphire solid surfaces The structure of the formed bilayer has been determined over the concentration range 0 2-7 4mM NaAOT It was found that the hydrocarbon tails pack at maximum packing limit at very low concentrations, and that the thickness of the bilayer was concentration-independent The adsorption was found to increase with concentration, with the surfactant molecules packing closer laterally The area per molecule was found to change from 138 +/- 25 to 51 +/- 4 angstrom(2) over the concentration range studied, with the thickness of the layer being constant at 33 2 A Addition of small amounts of salt was found to increase the surface excess, with the bilayer being thinner with a slightly larger area per molecule Addition of different salts of the same valency was found to have a very similiar effect, as had the addition of NaOH and HCl Hence, the effects of adding acid or base should be considered an effect of ionic strength rather than an effect of pH Adsorption of NaAOT to the sapphire surface that carries an opposite charge to the anionic surfactant is similar in many respects to the adsorption reported previously for hydrophilic and hydrophobic silica surfaces This suggests that the adsorption of NaAOT to a sui face is driven primarily by NaAOT self-assembly rather than effects of electrostatic at to the interface
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| 11. |
- Hellsing, Maja S., et al.
(författare)
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Scattering from Dilute and Lamellar Phase Solutions of Aerosol-OT Simultaneous Probe of Surface Structures and Bulk
- 2011
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Ingår i: Trends in colloid andinterface science XXIV. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642190377 ; , s. 139-142
-
Konferensbidrag (refereegranskat)abstract
- The benefits of simultaneous studies of adsorbed layers and bulk structures are shown for solutions of the surfactant Aerosol-OT. Above the critical micelle concentration, Aerosol-OT forms an aligned lamellar phase at the sapphire/solution interface which is in equilibrium with a bulk phase that consists of coexisting micellar solution and dispersed lamellar phase. Measurements of the aligned surface layers and the bulk scattering from a 2% wt solution by grazing incidence and small-angle neutron scattering show that the bulk consist of lamellar structures with the same d-spacing as seen at the surface but without the surface induced alignment. The surface lamellar structure corresponds to a 10% volume fraction for a 2% wt bulk which implies that there must be coexistence of regions of different concentration. Scattering patterns measured in grazing incidence geometry clearly show the relative contributions from small-angle scattering and specular reflectivity.
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| 12. |
- Hellsing, Maja S., et al.
(författare)
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Structure of a large colloidal crystal : controlling orientation and three-dimensional order
- 2012
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 2:18, s. 7091-7098
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Tidskriftsartikel (refereegranskat)abstract
- The three-dimensional crystal structure of charge stabilised polystyrene latex in deionised water was investigated by small-angle neutron diffraction. Crystallisation with a grain size of approximately 1 x 1 cm(2) was observed when the sample was flowed gently in to a 2 mm path cell. Bragg scattering peaks arising from the structure were observed under rotation about three perpendicular axes of the sample. The diffraction patterns indicate clearly that there is a cubic close packed structure with a 110 axis perpendicular to the cell wall. Rotations in small steps show large changes and indicate that the crystal is well oriented and has three-dimensional order. The crystal orientation was controlled by the meniscus and direction of flow when filling the cell.
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| 13. |
- Hellsing, Maja S., et al.
(författare)
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Structure of flocs of latex particles formed by addition of protein from Moringa seeds
- 2014
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 460, s. 460-467
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Tidskriftsartikel (refereegranskat)abstract
- Proteins extracted from the seeds of Moringa trees are effective flocculents for particles dispersed in water and are attractive as a natural and sustainable product for use in water purification. Studies with a model system consisting of polystyrene latex particles have shown that the protein adsorbs to the surface and causes flocculation as unusually dense aggregates. Small-angle neutron scattering that exploits contrast matching of deuterated latex particles dispersed in D2O to highlight bound protein has shown that the adsorbed amount reaches about 3 mg m(-2). The particles form very compact flocs that are characterized by fractal dimensions that approach the theoretical maximum of 3. Ultra small-angle neutron scattering allows these flocs to be characterized for a range of particle and protein concentrations. Proteins from two species of Moringa trees were investigated. The protein from Moringa stenopetala seeds gave rise to slightly lower fractal dimensions compared to Moringa oleifera, but still much larger than values observed for conventional ionic or polymeric flocculents that are in the range 1.75-2.3. Compact flocs are desirable for efficient separation of impurities and dewatering of sludge as well as other applications. A trend of increasing fractal dimension with particle concentration was observed when M. stenopetala seed protein was used and this resembles the behaviour predicted in Brownian dynamics simulation of flocculation. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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| 14. |
- Kwaambwa, Habauka M., et al.
(författare)
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Interactions of surfactants with a water treatment protein from Moringa oleifera seeds in solution studied by zeta-potential and light scattering measurements
- 2012
-
Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 97:4, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- Protein extracted from Moringa oleifera (MO) seeds has been advocated as a cheap and environmental friendly alternative to ionic flocculants for water purification. However, the nature and mechanism of its interaction with particles in water, as well as with dissolved surface-active molecules, are not well understood. In this article, we report studies of the protein and its interaction with four surfactants using dynamic light scattering (DLS), zeta-potential and turbidity measurements. Zeta-potential measurements identified points of charge reversal and the turbidity and DLS measurements were used to characterize the microstructure and size of protein-surfactant complexes. From the points of charge reversal, it was estimated that 7 anions are required to neutralize the positive charges of each protein molecule at pH 7. For protein mixtures with sodium dodecyl sulfate and dodecyl di-acid sodium salt, the peak in turbidity corresponds to concentrations with a large change in zeta-potential. No turbidity was observed for protein mixtures with either the nonionic surfactant Triton X-100 or the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate. Changes of pH in the range 410 have little effect on the zeta-potential, turbidity, and the hydrodynamic radius reflecting the high isoelectric point of the protein. Addition of small amounts of salt has little effect on the size of protein in solution. These results are discussed in the context of the use of the MO protein in water treatment.
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| 15. |
- Li, Ningning, et al.
(författare)
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Adsorption of non-ionic surfactants to the sapphire/solution interface : Effects of temperature and pH
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 369, s. 287-293
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of the non-ionic surfactants tetraoxyethylene glycol monododecyl ether (C12EO4), pentaoxyethylene glycol monododecyl ether (C12EO5), and hexaoxyethylene glycol monododecyl ether (C12EO6) to single crystal sapphire substrates has been studied using specular neutron reflection for solutions at the critical micelle concentration. The effects of temperature and pH of the solutions were studied as well as the differences between two different crystal faces, the C and the R planes. At neutral pH, significant adsorption was only observed when the temperature was raised above the cloud temperature. This adsorption was reversible and surfactant was displaced on cooling. Reducing the pH to 3 results in significantly increased adsorption of C12EO5 at 25 degrees C with a central layer consisting mainly of surfactant (about 90%) on the C-plane substrate. A slightly smaller surface excess was observed for the R-plane. This contrasts with the significantly lower density observed even at high temperatures at neutral pH on both substrates. The results suggest that for neutral solutions surfactant association above the cloud point is the primary driving force for adsorption. At low pH, specific interactions with protonated surfaces are important. The structures of the highly hydrated layers are similar to those found for the surfactants at hydrophilic silica surfaces.
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| 16. |
- Li, Ningning, et al.
(författare)
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Effect of pH, surface charge and counter-ions on the adsorption of sodium dodecyl sulfate to the sapphire/solution interface
- 2012
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 378, s. 152-158
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Tidskriftsartikel (refereegranskat)abstract
- The role of ionic interactions between sodium dodecyl sulfate, SDS, and sapphire surfaces have been studied using specular neutron reflection to determine the structure and composition of adsorbed surfactant layers. Increasing the pH of the solution from 3 to 9 reduces the adsorption by reversing the charge of the alumina. This occurs at lower pH for the R-plane (1 (1) over bar 02) than the C-plane (0001), corresponding to the different points of zero charge. The largest surface excess is about 6.5 mu mol m(-2), the thickness of the adsorbed layer is about 24 angstrom and it contains roughly 20% water. The hydrocarbon tails of the surfactant molecules clearly interpenetrate rather than form an ordered bilayer. The structure is similar in either pure water or in 0.1 M NaCl when the surfactant is at the respective critical micelle concentration. Different structures were seen with lithium and cesium dodecyl sulfate. The CsDS forms dense layers with little or no hydration and a surface excess of about 10.5 mu mol m(-2). The metal cation strongly influences the hydration of the adsorbed surfactant. An overall picture of 'flattened micelles' for the structure of the adsorbed layer is observed.
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| 17. |
- Linton, Peter, et al.
(författare)
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Evolution of structure and composition during the synthesis of mesoporous silica SBA-15 studied by small-angle neutron scattering
- 2011
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Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 13:4, s. 793-799
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Tidskriftsartikel (refereegranskat)abstract
- In-situ time-resolved small-angle neutron scattering (SANS) has been applied for the study of the formation of mesoporous silica SBA-15. The advantage of neutron scattering, compared to X-ray scattering, is the possibility to contrast match i.e. highlight certain parts of the sample. Three different solvents with different scattering contrasts were used for each synthesis. Three different silica sources (tetramethyl orthosilicate, tetraethyl orthosilicate and tetrapropyl orthosilicate) were used and in three cases salts (sodium chloride or sodium bromide) were added prior to addition of the silica source. Hence, the effect of the silica sources and of the salts, on the formation of SBA-15 was investigated. The main focus was on the evolution of the ordered hexagonal structure i.e. investigation of the (10) Bragg peak. In synchrotron SAXS measurements the intensity of the (10) Bragg peak continuously increases during the measurement. However, in the SANS measurements the (10) Bragg peak area decreases with time. The decrease of the (10) peak is highly dependent on the solvent, a larger fraction of D2O in the solvent results in a bigger reduction. The decrease is also more pronounced when salt is present in the synthesis. The reduction of intensity reflects the chemistry in the wall and is explained by the compositional change in the wall during the maturation of the hexagonal order.
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| 18. |
- Oleshkevych, Anna, et al.
(författare)
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Thermally driven redistribution of phases and components in Cu/Sn thin films
- 2012
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 535, s. 108-113
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Tidskriftsartikel (refereegranskat)abstract
- Unusual features of phase transformations under the thermal treatment of the thin films system Cu (80 nm)-Sn (20 nm) have been studied using a range of physical methods. Processes of mass transfer in thin layers were studied and regimes of thermal treatment were chosen to compare the influence of different temperatures for a given time and the influence of annealing time at a fixed temperature. Presence of the intermetallic phase Cu6Sn5 in the as-deposited state and its transformation into Cu3Sn phase after annealing at temperature 373 K for different times has been identified by grazing incidence X-ray diffraction. Annealing at a temperature of 473 K, and higher, leads to the formation, unexpectedly, of the Cu4Sn phase. The concentration distribution of tin through the depth of the sample was obtained by Rutherford backscattering spectroscopy and demonstrated the existence of the Cu4Sn composition. The topography of the surface of the samples was determined with atomic-force microscopy.
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| 19. |
- Olsson, Anders, et al.
(författare)
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A holder to rotate sample cells to avoid sedimentation in small-angle neutron scattering and ultra small-angle neutron scattering experiments
- 2013
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Ingår i: Measurement science and technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 24:10, s. 105901-
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentation, or creaming, of samples can significantly alter the amount of material in the beam during small-angle scattering experiments. Simple rotating mounts that ameliorate this effect are described and the design criteria are carefully discussed. A modular design permits simple adaptation to various instruments and different sample cells. Temperature control in the range 10 degrees C below ambient to about +40 degrees C has been implemented using air flow and a Peltier device. Example ultra small-angle neutron scattering data are shown that exploit the simplicity of the mounts and the capability to position several samples close together on a translation stage.
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| 20. |
- Pálsson, Gunnar K., et al.
(författare)
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Deuterium-induced volume expansion in Fe0.5V0.5/V superlattices
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:24, s. 245424-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry was used to investigate the deuterium uptake in a thin metal superlattice that displays an anisotropic elastic response [Fe0.5V0.5/V (6/21 monolayers)]. We see evidence of the presence of a coexistence region which has never before been seen in vanadium-based superlattices. The loading process is completely reversible from which we conclude that the phases must be coherent, in stark contrast to bulk VDx, where the two-phase region displays hysteresis. The deuterium-induced volume expansion exhibits changes in slope that correlate with the plateau region and the expansion is comparable and even larger than in the bulk. The spectacular cooperation between the elastic fields seems to be found only in one-dimensionally confined structures with biaxial compressive strain states.
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| 21. |
- Qazi, S. Junaid S., et al.
(författare)
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Alignment of Dispersions of Plate-Like Colloidal Particles of Ni(OH)(2) Induced by Elongational Flow
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 115:13, s. 3271-3280
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Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering, SANS, has been used to study the alignment of a sterically stabilized colloidal dispersion of nickel hydroxide induced by elongational flow. Two different concentrations, 20 and 23 wt %, of well-defined hexagonal platelets have been studied. Significant anisotropy in the scattering patterns has been observed for the higher concentration dispersion that increases with increasing elongational strain rate. The effect of pipe flow (shear flow) on the orientational ordering at the inlets is also described. Near the outlets there is also a shear stress and this tends to increase the alignment. The orientational distribution of the particles under flow is described in terms of an order parameter calculated with respect to an individual director for each scattering pattern. The experimental measurements are supported by comparison with computer simulations which help to explain the effects of local velocity on the alignment induced by elongational flow. A slight decrease in the observed alignment was found after continuous flow for approximately 30 min and possible reasons are discussed.
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| 22. |
- Qazi, S. Junaid S., et al.
(författare)
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Alignment of Plate-Like Particles in a Colloidal Dispersion under Flow in a Uniform Pipe Studied by High-Energy X-ray Diffraction
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:24, s. 18701-18709
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Tidskriftsartikel (refereegranskat)abstract
- High-energy angle-dispersive X-ray diffraction has been used to study the alignment of colloidal suspension of kaolinite particles in water as they flow along a pipe. X-rays with energies above 25 keV have a major advantage, as they can penetrate through thick samples and walls of containers and permit investigation of samples under realistic flow conditions. As an example of the method, flow through a circular cross-section pipe with an internal diameter of 5 mm has been studied: this is typical of industrial applications. The angular distribution of intensities of peaks in the diffraction pattern as a function of the location of the pipe in the X-ray beam provides information about the alignment of particles under flow. Order parameters have been calculated to describe the alignment and direction of orientation. It is observed that the particles align in the direction of flow with their flat faces parallel to the flow. The experimental results are compared with the calculations of the local strain rate that help to explain the onset of alignment of the particles.
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| 23. |
- Qazi, S. Junaid S., et al.
(författare)
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Dispersions of plate-like colloidal particles : Cubatic order?
- 2010
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 348:1, s. 80-84
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Tidskriftsartikel (refereegranskat)abstract
- Experimental evidence for the existence of 'cubatic' order in a colloidal dispersion of plate-like particles is presented. In a 'cubatic' phase, disk-like particles self-assemble with domains of a few parallel plates and the director tends to be orthogonal in adjacent domains. This phase has been predicted previously by computer simulation. The domains are approximately equiaxial and are predicted to exist only within a limited range of aspect ratios and volume fractions. This locally ordered structure cannot be identified readily using scattering techniques, since the patterns are expected to be similar to those of isotropic liquid phases. For this reason, we have used a real-space technique of cryo-transmission electron microscopy that directly probes such locally ordered structures to study dispersions of nickel hydroxide particles. Polydispersity of particle size is expected to require some local tilting in order to include larger particles in a dense structure and this is discussed with respect to the concentration range for which cubatic order is observed. This new structure offers the possibility of novel materials that could be prepared by self-assembly and have applications in a wide range of fields.
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| 24. |
- Qazi, S. Junaid S., et al.
(författare)
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Impact of Ni(OH)(2) Platelike Particles on Lamellar Surfactant Mesophases and the Orientation of Their Mixtures under Elongational Flow
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 115:35, s. 10413-10424
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the behavior under elongational flow of mixtures of lamellar fragments and platelike colloidal particles. Mixtures of a dialkyl chain cationic surfactant, DHTAC (15 wt %), and the nonionic surfactant Brij 97 (0.5 wt %) form dispersions of lamellar phase fragments, and these were studied in the presence of smaller platelike colloidal particles of Ni(OH)(2) stabilized with sodium polyacrylate. Small-angle neutron scattering was used to follow the changes in the lamellar phase fragments in the mixture under elongational flow. The addition of a small fraction of the Ni(OH)(2) dispersion resulted in significantly increased viscosity and reduced the structure and size of the lamellar fragments, and this effect was further enhanced because of the flow induced alignment. The behavior of the mixture under elongational flow is described, and the induced orientation is discussed in terms of order parameters at the different positions using spatially resolved small-angle scattering. The effect of flow rate on the orientational alignment in the mixture is also described.
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| 25. |
- Qazi, S. Junaid S., et al.
(författare)
-
Orientation of a Dispersion of Kaolinite Flowing in a Jet
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:8, s. 3704-3713
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Tidskriftsartikel (refereegranskat)abstract
- Orientational alignment in a dilute dispersion of kaolinite particles has been investigated in a flow pattern that combines both shear and elongational stress, namely flow at a jet created by a 2 mm diameter nozzle inserted in a 6 mm diameter pipe. Spatially-resolved X-ray diffraction with synchrotron radiation permits detailed maps of the alignment to be deduced and compared with fluid mechanics calculations of the flow. The angular distribution of diffracted intensity from a given position in the pipe provides information about the orientation distribution of the particles. This is quantified and presented in terms of order parameters. The cone-shaped nozzle provides a jet of liquid giving a high degree of alignment of the particles that is uniform along lines across the conical section and constant in the small straight-sided region at the exit of the nozzle. The vortex motion that arises from the flow with a modest Reynolds number could be determined as well as the tendency for some particles to align with their large faces perpendicular to the overall flow direction at the flat surface of the nozzle outlet.
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| 26. |
- Rennie, Adrian R., et al.
(författare)
-
Diffusion Phase Formation in the Cu-Sn Nanofilms System
- 2011
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Ingår i: Grain Boundary Diffusion, Stresses and Segregation. - 9783037850558 ; , s. 167-176
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Processes involved in the structure and phase formation in the thin film systems Sn(4 nm)/Cu(14 nm) and Cu(14 nm)/Sn(8 nm) in the temperature range 130-500 degrees C were studied using "in situ" electron imaging and Transmission Electron Microscopy methods (TEM). Solubility of Sn alpha - solid solution Cu-Sn has been determined from the changes in the lattice parameter. This work was performed in the framework of the Swedish Institute supported cooperative research project "Thin metal films - the interplay of structure diffusion and boundaries" (SI dnr 00699/2009).
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| 27. |
- Rennie, Adrian R., et al.
(författare)
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Learning about SANS instruments and data reduction from round robin measurements on samples of polystyrene latex
- 2013
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 46:5, s. 1289-1297
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of a well-characterized `standard' sample can verify the performance of an instrument. Typically, small-angle neutron scattering instruments are used to investigate a wide range of samples and may often be used in a number of configurations. Appropriate `standard' samples are useful to test different aspects of the performance of hardware as well as that of the data reduction and analysis software. Measurements on a number of instruments with different intrinsic characteristics and designs in a round robin can not only better characterize the performance for a wider range of conditions but also, perhaps more importantly, reveal the limits of the current state of the art of small-angle scattering. The exercise, followed by detailed analysis, tests the limits of current understanding as well as uncovering often forgotten assumptions, simplifications and approximations that underpin the current practice of the technique. This paper describes measurements of polystyrene latex, radius 720 Å, with a number of instruments. Scattering from monodisperse, uniform spherical particles is simple to calculate and displays sharp minima. Such data test the calibrations of intensity, wavelength and resolution as well as the detector response. Smoothing due to resolution, multiple scattering and polydispersity has been determined. Sources of uncertainty are often related to systematic deviations and calibrations rather than random counting errors. The study has prompted development of software to treat modest multiple scattering and to better model the instrument resolution. These measurements also allow checks of data reduction algorithms and have identified how they can be improved. The reproducibility and the reliability of instruments and the accuracy of parameters derived from the data are described.
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| 28. |
- Tynkova, A., et al.
(författare)
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Interdiffusion in Au(120 nm)/Ni(70 nm) thin films at the low-temperature annealing in the different atmospheres
- 2013
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 87, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- The development of the interdiffusion processes and the surface morphology changes in thin films of Au(120 nm)/Ni(70 nm) during annealing at 200 degrees C for 20 min in vacuum with different residual atmosphere pressures of 10(-3) and 10(-6) Pa and in an environment of hydrogen at a pressure of 5 x 10(2) Pa have been studied. Secondary ion mass spectrometry, Auger electron spectroscopy, X-ray diffraction, optical microscopy, atomic force microscopy and scanning electron microscopy were used. Surface microdefects that form in the films are related to the local oxidation of nickel and to the stress that arises due to interdiffusion. Defect formation and reactions at the surface are found to be controlling factors in the transport of nickel to the surface and in the observed morphology.
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