| 1. |
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| 2. |
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| 3. |
- Ericsson, A., et al.
(författare)
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Crystallization of a Zr-based metallic glass produced by laser powder bed fusion and suction casting
- 2021
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier. - 0022-3093 .- 1873-4812. ; 571
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Tidskriftsartikel (refereegranskat)abstract
- The crystallization behaviour during low temperature annealing of samples of the Zr59.3Cu28.8Al10.4Nb1.5 (at%) bulk metallic glass produced by suction casting and the laser powder bed fusion (LPBF) process were studied with small angle neutron scattering (SANS), X-ray diffraction and scanning electron microscopy. The in-situ SANS measurements during isothermal annealing reveals that the phase separation in the LPBF processed material proceeds at a smaller characteristic length-scale than the cast material. Quantitative analysis of the SANS data shows that, while the crystallization process in both materials proceed through rapid nucleation followed by diffusion limited growth, the LPBF processed material crystallizes with a smaller cluster size and at a higher rate. The smaller cluster size is attributed to the elevated oxygen content in the LPBF processed material which reduces the nucleation barrier and thus the thermal stability.
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| 4. |
- Hemming, Joanna M., et al.
(författare)
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Environmental Pollutant Ozone Causes Damage to Lung Surfactant Protein B (SP-B)
- 2015
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 54:33, s. 5185-5197
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Tidskriftsartikel (refereegranskat)abstract
- Lung surfactant protein B (SP-B) is an essential protein found in the surfactant fluid at the air water interface of the lung. Exposure to the air pollutant ozone could potentially damage SP-B and lead to respiratory distress. We have studied two peptides, one consisting of the N-terminus of SP-B [SP-B(1-25)] and the other a construct of the N- and C-termini of SP-B [SP-B-(1-25,B-63-78)], called SMB. Exposure to dilute levels of ozone (similar to 2 ppm) of monolayers of each peptide at the air water interface leads to a rapid reaction, which is evident from an increase in the surface tension. Fluorescence experiments revealed that this increase in surface tension is accompanied by a loss of fluorescence from the tryptophan residue at the interface. Neutron and X-ray reflectivity experiments show that, in contrast to suggestions in the literature, the peptides are not solubilized upon oxidation but rather remain at the interface with little change in their hydration. Analysis of the product material reveals that no cleavage of the peptides occurs, but a more hydrophobic product is slowly formed together with an increased level of oligomerization. We attributed this to partial unfolding of the peptides. Experiments conducted in the presence of phospholipids reveal that the presence of the lipids does not prevent oxidation of the peptides. Our results strongly suggest that exposure to low levels of ozone gas will damage SP-B, leading to a change in its structure. The implication is that the oxidized protein will be impaired in its ability to interact at the air water interface with negatively charged phosphoglycerol lipids, thus compromising what is thought to be its main biological function.
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| 5. |
- Larsen, Simon R., et al.
(författare)
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Sample cell for studying liquid interfaces with an in situ electric field using X-ray reflectivity and application to clay particles at oil–oil interfaces
- 2018
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 25:Part: 3, s. 915-917
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Tidskriftsartikel (refereegranskat)abstract
- Commissioning results of a liquid sample cell for X-ray reflectivity studies with an in situ applied electrical field are presented. The cell consists of a Plexiglas container with lateral Kapton windows for air-liquid and liquid-liquid interface studies, and was constructed with grooves to accept plate electrodes on the walls parallel to the direction of the beam. Both copper and ITO plate electrodes have been used, the latter being useful for simultaneous optical studies. Commissioning tests were made at the I07 beamline of the Diamond Light Source.
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| 6. |
- 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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| 7. |
- 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
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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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| 8. |
- 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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| 9. |
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| 10. |
- Berts, Ida, 1984-, et al.
(författare)
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Controlling adsorption of albumin with hyaluronan on silica surfaces and sulfonated latex particles
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 504, s. 315-324
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Tidskriftsartikel (refereegranskat)abstract
- Polysaccharides are known to modify binding of proteins at interfaces and this paper describes studies of these interactions and how they are modified by pH. Specifically, the adsorption of human serum albumin on to polystyrene latex and to silica is described, focusing on how this is affected by hyaluronan. Experiments were designed to test how such binding might be modified under relevant physiological conditions. Changes in adsorption of albumin alone and the co-adsorption of albumin and hyaluronan are driven by electrostatic interactions. Multilayer binding is found to be regulated by the pH of the solution and the molecular mass and concentration of hyaluronan. Highest adsorption was observed at pH below 4.8 and for low molecular mass hyaluronan (<= 150 kDa) at concentrations above 2 mg ml(-1). On silica with grafted hyaluronan, albumin absorption is reversed by changes in solvent pH due to their strong electrostatic attraction. Albumin physisorbed on silica surfaces is also rinsed away with dilute hyaluronan solution at pH 4.8. The results demonstrate that the protein adsorption can be controlled both by changes of pH and by interaction with other biological macromolecules.
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| 11. |
- 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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| 12. |
- 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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| 13. |
- 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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| 14. |
- Berts, Ida, et al.
(författare)
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Tuning the density profile of surface-grafted hyaluronan and the effect of counter-ions
- 2013
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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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| 15. |
- Cárdenas, Marité, et al.
(författare)
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Human Saliva Forms a Complex Film Structure on Alumina Surfaces
- 2007
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:1, s. 65-69
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Tidskriftsartikel (refereegranskat)abstract
- Films formed from saliva on surfaces are important for the maintenance of oral health and integrity by protection against chemical and/or biological agents. The aim of the present study was to investigate adsorbed amounts, thickness, and structure of films formed from human whole saliva on alumina surfaces by means of in situ ellipsometry, neutron reflectivity, and atomic force microscopy. Alumina (Al2O3, synthetic sapphire) is a relevant and interesting substrate for saliva adsorption studies as it has an isoelectric point close to that of tooth enamel. The results showed that saliva adsorbs rapidly on alumina. The film could be modeled in two layers: an inner and dense thin region that forms a uniform layer and an outer, more diffuse and thicker region that protrudes toward the bulk of the solution. The film morphology described a uniformly covering dense layer and a second outer layer containing polydisperse adsorbed macromolecules or aggregates.
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| 16. |
- Chien, Yu-Chuan, 1990-, et al.
(författare)
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Correlations between precipitation reactions and electrochemical performance of lithium-sulfur batteries probed by operando scattering techniques
- 2022
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Ingår i: Chem. - : Elsevier. - 2451-9294. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive description of electrochemical processes in the positive electrode of lithium-sulfur batteries is crucial for the utilization of active material. However, the discharge mechanisms are complicated due to various reactions in multiple phases and the tortuosity of the highly porous carbon matrix. In this work, simultaneous measurements of small-angle and wide-angle scattering and cell resistance are performed on operating lithium-sulfur cells. Results indicate that precipitates grow mostly in number, not in size, and that the structure of the carbon matrix is not affected. The comparison of the small-angle and wide-angle scattering reveals the amorphous discharge products found at a low discharge rate. Further analysis demonstrates the correlation between the diffusion resistance and the compositional change of electrolyte in the mesopores at the end of discharge, which suggests that Li-ion deficiency is the limiting factor for sulfur utilization at a medium discharge rate.
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| 17. |
- Chien, Yu-Chuan, 1990-, et al.
(författare)
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Mechanistic Insights on the Mesoscale in the Positive Electrode of Lithium–Sulfur Batteries
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A comprehensive description of the electrochemical processes in the positive electrodeof lithium–sulfur batteries is critical to the enhancement of sulfur utilization. However,the discharge mechanisms are complicated due to the various reactions in multiplephases and the tortuosity of the highly porous carbon matrix. While previous studieshave focused on the precipitation of Li2S, the effect of the limited mass transport insidethe micro-/mesopores of an electrode with optimized surface area have largely beenneglected. In this work, operando small-angle scattering with three different contrasts,and wide-angle scattering, has been performed with simultaneous resistance measure-ment of internal and diffusion. The results indicate that both electrode passivation andcomplete pore blockage are unlikely since the precipitates are surrounded by the elec-trolyte and grow mostly in number, not in size. The difference between the small- andwide-angle scattering reveals the amorphous discharge products at a low C-rate. Furtheranalyses demonstrate the correlation between the diffusion resistance and the contrastin the mesopores at the end of discharge, which suggests that Li-ion deficiency is thelimiting factor of sulfur utilization at a medium C-rate.
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| 18. |
- Cockcroft, Jeremy K., et al.
(författare)
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Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:47, s. 25945-25951
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Tidskriftsartikel (refereegranskat)abstract
- A homologous series of n-alkyl trimethylammonium bromide surfactants, H(CH2)(n)N+(CH3)(3) Br-, from C(10)TAB to C(18)TAB have been studied systematically in the bulk over a wide range of temperatures. Common features in the structures are identified, with packing dominated by the co-ordination of the cationic head groups with bromide anions and interdigitation of the hydrocarbon chains. This arrangement provides an explanation for the thin adsorbed bilayers that have been observed at various hydrophilic surfaces from aqueous solutions in previous studies. The molecular volumes and arrangement are comparable with structures of a number of different self-assembled amphiphiles. For these surfactants with bromide counter-ions, formation of crystal hydrates was not observed. The alkyl chains are highly mobile and at high temperatures a plastic phase is found for all materials with a transition enthalpy that is similar to the melting enthalpy of many long alkyl chains. Other unexpected phase transitions depend more markedly on the hydrocarbon chain length and evidently depend on delicate balances of the various contributions to the free energy.
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| 19. |
- Dicko, Cedric, et al.
(författare)
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NUrF-Optimization of in situ UV-vis and fluorescence and autonomous characterization techniques with small-angle neutron scattering instrumentation
- 2020
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Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 91:7
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Tidskriftsartikel (refereegranskat)abstract
- We have designed, built, and validated a (quasi)-simultaneous measurement platform called NUrF, which consists of neutron small-angle scattering, UV-visible, fluorescence, and densitometry techniques. In this contribution, we illustrate the concept and benefits of the NUrF setup combined with high-performance liquid chromatography pumps to automate the preparation and measurement of a mixture series of Brij35 nonionic surfactants with perfluorononanoic acid in the presence of a reporter fluorophore (pyrene).
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| 20. |
- Gustafsson, Emil, et al.
(författare)
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Understanding interactions of plasticisers with a phospholipid monolayer
- 2024
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 20:13, s. 2892-2899
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Tidskriftsartikel (refereegranskat)abstract
- The use of DEHP (diethylhexyl phthalate) is now banned for most applications in Europe; the exception is for blood bags, where its toxicity is overshadowed by its ability to extend the storage life of red blood cells. Another plasticiser, BTHC (butanoyl trihexyl citrate), is used in paediatric blood bags but does not stabilise blood cells as effectively. Interactions between plasticisers and lipids are investigated with a phospholipid, DMPC, to understand the increased stability of blood cells in the presence of DEHP as well as bioaccumulation and identify differences with BTHC. Mixed monolayers of DMPC and DEHP or BTHC were studied on Langmuir troughs where surface pressure/area isotherms can be measured. Neutron reflection measurements were made to determine the composition and structure of these mixed layers. A large amount of plasticiser can be incorporated into a DMPC monolayer but once an upper limit is reached, plasticiser is selectively removed from the interface at high surface pressures. The upper limit is found to occur between 40–60 mol% for DEHP and 20–40 mol% for BTHC. The areas per molecule are also different with DEHP being in the range of 50–100 Å2 and BTHC being 65–120 Å2. Results indicate that BTHC does not fit as well as DEHP in DMPC monolayers which could help explain the differences observed with regards to the stability of blood cells.
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| 21. |
- Gustafsson, Emil, et al.
(författare)
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Understanding interactions of plasticisers with a phospholipid monolayer
- 2024
-
Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 20:13, s. 2892-2899
-
Tidskriftsartikel (refereegranskat)abstract
- The use of DEHP (diethylhexyl phthalate) is now banned for most applications in Europe; the exception is for blood bags, where its toxicity is overshadowed by its ability to extend the storage life of red blood cells. Another plasticiser, BTHC (butanoyl trihexyl citrate), is used in paediatric blood bags but does not stabilise blood cells as effectively. Interactions between plasticisers and lipids are investigated with a phospholipid, DMPC, to understand the increased stability of blood cells in the presence of DEHP as well as bioaccumulation and identify differences with BTHC. Mixed monolayers of DMPC and DEHP or BTHC were studied on Langmuir troughs where surface pressure/area isotherms can be measured. Neutron reflection measurements were made to determine the composition and structure of these mixed layers. A large amount of plasticiser can be incorporated into a DMPC monolayer but once an upper limit is reached, plasticiser is selectively removed from the interface at high surface pressures. The upper limit is found to occur between 40-60 mol% for DEHP and 20-40 mol% for BTHC. The areas per molecule are also different with DEHP being in the range of 50-100 Å2 and BTHC being 65-120 Å2. Results indicate that BTHC does not fit as well as DEHP in DMPC monolayers which could help explain the differences observed with regards to the stability of blood cells.
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| 22. |
- 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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| 23. |
- Hellsing, Maja S., et al.
(författare)
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Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
- 2012
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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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| 24. |
- 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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| 25. |
- 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
-
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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| 26. |
- Hellsing, Maja S., et al.
(författare)
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Structure of a large colloidal crystal : controlling orientation and three-dimensional order
- 2012
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 2:18, s. 7091-7098
-
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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| 27. |
- Hellsing, Maja S., et al.
(författare)
-
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
-
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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| 28. |
- Hemming, Joanna M., et al.
(författare)
-
Changes to lung surfactant monolayers upon exposure to gas phase ozone observed using X-ray and neutron reflectivity
- 2022
-
Ingår i: Environmental Science. - : Royal Society of Chemistry. - 2634-3606. ; 2:4, s. 753-760
-
Tidskriftsartikel (refereegranskat)abstract
- Exposure to the secondary pollutant ozone in ambient air is associated with adverse health effects when inhaled. In this work we use surface pressure measurements, combined with X-ray and neutron reflection, to observe changes in a layer of lung surfactant at the air water interface when exposed to gas phase ozone. The results demonstrate that the layer reacts with ozone changing its physical characteristics. A slight loss of material, a significant thinning of the layer and increased hydration of the surfactant material is observed. The results support the hypothesis that unsaturated lipids present in lung surfactant are still susceptible to rapid reaction with ozone and the reaction changes the properties of the interfacial layer.
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| 29. |
- Jones, Stephanie H., et al.
(författare)
-
Aqueous Radical Initiated Oxidation of an Organic Monolayer at the Air-Water Interface as a Proxy for Thin Films on Atmospheric Aerosol Studied with Neutron Reflectometry
- 2023
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:42, s. 8922-8934
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry has been used to study the radical initiated oxidation of a monolayer of the lipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) at the air–solution interface by aqueous-phase hydroxyl, sulfate, and nitrate radicals. The oxidation of organic films at the surface of atmospheric aqueous aerosols can influence the optical properties of the aerosol and consequently can impact Earth’s radiative balance and contribute to modern climate change. The amount of material at the air–solution interface was found to decrease on exposure to aqueous-phase radicals which was consistent with a multistep degradation mechanism, i.e., the products of reaction of the DSPC film with aqueous radicals were also surface active. The multistep degradation mechanism suggests that lipid molecules in the thin film degrade to form progressively shorter chain surface active products and several reactive steps are required to remove the film from the air–solution interface. Bimolecular rate constants for oxidation via the aqueous phase OH radical cluster around 1010 dm3 mol–1 s–1. Calculations to determine the film lifetime indicate that it will take ∼4–5 days for the film to degrade to 50% of its initial amount in the atmosphere, and therefore attack by aqueous radicals on organic films could be atmospherically important relative to typical atmospheric aerosol lifetimes.
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| 30. |
- Jones, Stephanie H., et al.
(författare)
-
Are organic films from atmospheric aerosol and sea water inert to oxidation by ozone at the air-water interface?
- 2017
-
Ingår i: Atmospheric Environment. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1352-2310 .- 1873-2844. ; 161, s. 274-287
-
Tidskriftsartikel (refereegranskat)abstract
- The heterogeneous oxidation of thin films of organic material extracted from real aerosol and sea-water samples was studied at the air-water interface using X-ray reflectivity. Oxidation of thin films of organic material extracted from real aerosol and sea-water is important in further understanding the impact of coated aerosols on the climate of the Earth. Surface active insoluble organic material extracted from the atmosphere was found to form stable films at the air-water interface (thickness measured as 10-14 nm). On exposure of the films to gas-phase ozone, no reaction (or change in the relative scattering length of the interface) was observed, indicating a potential lack of unsaturated organic material in the samples. Gas chromatography and electrospray ionization mass spectrometry showed the presence of saturated compounds in the samples. It is therefore proposed that the amount of unsaturated compounds as compared to saturated compounds in the atmospheric material is so low that the mass spectrometry analyses, as well as gas-phase oxidation are dominated by saturated material. A reaction was observed on exposure of the same films to aqueous phase hydroxyl and nitrate radicals and a film thinning mechanism is proposed to explain the change in scattering length of the film at the air-water interface. It can be suggested tentatively that oxidation by gas-phase ozone is not important in the atmosphere for organic films on aqueous atmospheric aerosol and that further studies should focus on radical induced oxidation of saturated organic material instead of unsaturated proxies that are typically studied.
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| 31. |
- King, Martin D., et al.
(författare)
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Oxidation of oleic acid at the air-water interface and its potential effects on cloud critical supersaturations
- 2009
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:35, s. 7699-7707
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of organic films on cloud condensation nuclei has the potential to affect climate and precipitation events. In this work we present a study of the oxidation of a monolayer of deuterated oleic acid (cis-9-octadecenoic acid) at the air-water interface by ozone to determine if oxidation removes the organic film or replaces it with a product film. A range of different aqueous sub-phases were studied. The surface excess of deuterated material was followed by neutron reflection whilst the surface pressure was followed using a Wilhelmy plate. The neutron reflection data reveal that approximately half the organic material remains at the air-water interface following the oxidation of oleic acid by ozone, thus cleavage of the double bond by ozone creates one surface active species and one species that partitions to the bulk (or gas) phase. The most probable products, produced with a yield of similar to(87 +/- 14)%, are nonanoic acid, which remains at the interface, and azelaic acid (nonanedioic acid), which dissolves into the bulk solution. We also report a surface bimolecular rate constant for the reaction between ozone and oleic acid of (7.3 +/- 0.9) x 10(-11) cm(2) molecule s(-1). The rate constant and product yield are not affected by the solution sub-phase. An uptake coefficient of ozone on the oleic acid monolayer of similar to 4 x 10(-6) is estimated from our results. A simple Kohler analysis demonstrates that the oxidation of oleic acid by ozone on an atmospheric aerosol will lower the critical supersaturation needed for cloud droplet formation. We calculate an atmospheric chemical lifetime of oleic acid of 1.3 hours, significantly longer than laboratory studies on pure oleic acid particles suggest, but more consistent with field studies reporting oleic acid present in aged atmospheric aerosol.
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| 32. |
- Kwaambwa, Habauka M., et al.
(författare)
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Interaction of Moringa oleifera seed protein with a mineral surface and the influence of surfactants
- 2015
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 448, s. 339-346
-
Tidskriftsartikel (refereegranskat)abstract
- The paper describes the adsorption of purified protein from seeds of Moringa olelfera to a sapphire interface and the effects of addition of the anionic surfactant sodium dodecylsulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). Neutron reflection was used to determine the structure and composition of interfacial layers adsorbed at the solid/solution interface. The maximum surface excess of protein was found to be about 5.3 mg m(-2). The protein does not desorb from the solid/liquid interface when rinsed with water. Addition of SDS increases the reflectivity indicating co-adsorption. It was observed that CTAB is able to remove the protein from the interface. The distinct differences to the behavior observed previously for the protein at the silica/water interface are identified. The adsorption of the protein to alumina in addition to other surfaces has shown why it is an effective flocculating agent for the range of impurities found in water supplies. The ability to tailor different surface layers in combination with various surfactants also offers the potential for adsorbed protein to be used in separation technologies.
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| 33. |
- Kwaambwa, Habauka M., et al.
(författare)
-
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
-
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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| 34. |
- Li, Ningning, et al.
(författare)
-
Adsorption of non-ionic surfactants to the sapphire/solution interface : Effects of temperature and pH
- 2012
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 369, s. 287-293
-
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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| 35. |
- Li, Ningning, et al.
(författare)
-
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
-
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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| 36. |
- Li, Ning Ning, et al.
(författare)
-
Neutron reflectometry of anionic surfactants on sapphire : A strong maximum in the adsorption near the critical micelle concentration
- 2016
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 471, s. 81-88
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of the anionic surfactants, lithium, sodium and cesium dodecylsulfates, and sodium decylsulfonate, on the positively charged C-plane (0001) of sapphire (alumina) has been measured using neutron reflection. For each of the four surfactants there is a strong maximum in the adsorption at about the critical micelle concentration. The maximum becomes more marked from lithium to cesium. The measurements were reproduced over a range of different physical conditions and could not be accounted for in terms of impurities. The maximum is explained quantitatively by using the combination of a mass action model to calculate the mean activity of the surfactant, and a cooperative model of the adsorption (Frumkin), in which saturation of the layer is not attained until well above the critical micelle concentration.
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| 37. |
- Linton, Peter, et al.
(författare)
-
Evolution of structure and composition during the synthesis of mesoporous silica SBA-15 studied by small-angle neutron scattering
- 2011
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 13:4, s. 793-799
-
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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| 38. |
- Linton, Peter, et al.
(författare)
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In Situ Observation of the Genesis of Mesoporous Silica SBA-15 : Dynamics on Length Scales from 1 nm to 1 mu m
- 2009
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:8, s. 4685-4691
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Tidskriftsartikel (refereegranskat)abstract
- We report on the mechanism of growth of mesoporous silica (SBA-15, plane group p6m). In situ studies of the formation using ultrasmall angle X-ray scattering (USAXS) and small-angle X-ray scattering (SAXS) covering length scales from 5 to 10000 A, complemented with UV-vis and transmission electron microscopy (TEM), provide unique data on particle growth coupled with information regarding the progression of the mesostructure formation and the micellar evolution.
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| 39. |
- Lundquist, Anna, et al.
(författare)
-
Melittin–Lipid interaction : A comparative study using liposomes, micelles and bilayer disks
- 2008
-
Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 1879-2642. ; 1778:10, s. 2210-2216
-
Tidskriftsartikel (refereegranskat)abstract
- Comparison of melittin interaction with liposomes, bilayer disks and micelles showed that melittin binding to lipid aggregates is largely dictated by the amount of highly curved areas in the aggregates. The PEG-stabilised bilayer disks were characterised by a combination of small angle neutron scattering, cryo-transmission electron microscopy and dynamic light scattering. Importantly, the theoretically foreseen partial segregation of the lipid components, important for maintaining the structure of the bilayer disk, was confirmed. Steady state fluorescence spectroscopy indicated that melittin mainly resides at the rim of the bilayer disks. Results of the present study help increase the understanding of the mechanisms behind, and the physico-chemical factors affecting, melittin–lipid interaction. We suggest that bilayer disks, due to their stable structure, constitute interesting vehicles for transport of peptides that have high propensity to associate with lipid surfaces of high curvature.
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| 40. |
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| 41. |
- Moulin, Martine, et al.
(författare)
-
Perdeuteration of cholesterol for neutron scattering applications using recombinant Pichia pastoris
- 2018
-
Ingår i: Chemistry and Physics of Lipids. - : Elsevier. - 0009-3084 .- 1873-2941. ; 212, s. 80-87
-
Tidskriftsartikel (refereegranskat)abstract
- Deuteration of biomolecules has a major impact on both quality and scope of neutron scattering experiments. Cholesterol is a major component of mammalian cells, where it plays a critical role in membrane permeability, rigidity and dynamics, and contributes to specific membrane structures such as lipid rafts. Cholesterol is the main cargo in low and high-density lipoprotein complexes (i.e. LDL, HDL) and is directly implicated in several pathogenic conditions such as coronary artery disease which leads to 17 million deaths annually. Neutron scattering studies on membranes or lipid-protein complexes exploiting contrast variation have been limited by the lack of availability of fully deuterated biomolecules and especially perdeuterated cholesterol. The availability of perdeuterated cholesterol provides a unique way of probing the structural and dynamical properties of the lipoprotein complexes that underly many of these disease conditions. Here we describe a procedure for in vivo production of perdeuterated recombinant cholesterol in lipid-engineered Pichia pastoris using flask and fed batch fermenter cultures in deuterated minimal medium. Perdeuteration of the purified cholesterol was verified by mass spectrometry and its use in a neutron scattering study was demonstrated by neutron reflectometry measurements using the FIGARO instrument at the ILL.
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| 42. |
- Nouhi, Shirin, et al.
(författare)
-
Comparative study of flocculation and adsorption behaviour of water treatment proteins from Moringa peregrina and Moringa oleifera seeds
- 2019
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Trees of Moringa oleifera are the most widely exploited species of Moringa and proteins extracted from its seeds have been identified as the most efficient natural coagulant for water purification. Largely for climatic reasons, other Moringa species are more accessible in some regions and this paper presents a comparative study of the adsorption to different materials of the proteins extracted from seeds of Moringa peregrina and Moringa oleifera to explore their use as flocculating agents in regions where each is more readily accessible. Results showed that Moringa peregrina seed proteins had higher adsorption to alumina compared to silica, in contrast to opposite behavior for Moringa oleifera. Both species provide cationic proteins that can act as effective coagulants for the various impurities with different surface potential. Despite the considerable similarity of the amino acid composition, the seed proteins have significantly different adsorption and this presents the opportunity to improve processes by choosing the optimal species or combination of species depending on the type of impurity or possible development of separation processes.
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| 43. |
- Nouhi, Shirin, et al.
(författare)
-
Distortion of surfactant lamellar phases induced by surface roughness
-
Tidskriftsartikel (refereegranskat)abstract
- Self-assembly is a characteristic property of soft matter and understanding the factors which assist or perturb this process is of a great importance in many biological and industrial processes. Amphiphiles self-assemble and order into a variety of structures including well-ordered lamellar phases. The present work uses neutron reflectometry to explore the effects of both interface roughness and temperature on the lamellar-phase structure of a non-ionic surfactant at a solid/liquid interface. The structure of concentrated solutions of tetraethyleneglycol dodecyl ether has been compared against a smooth surface and one with a roughness of the order of the lamellar spacing. The results showed that the surfactant forms a well-order and aligned structure at smooth surface that extends to a depth of micrometers from the interface. Increasing the temperature of the sample and subsequent cooling helped the alignment and increased the number of oriented layers at the surface. The same sample formed a significantly less aligned structure at a rough surface that did not align to same extent after heating. The perturbation of the structure caused by thermal fluctuations was found to be much less than that imposed by a small surface roughness. Keywords
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| 44. |
- Nouhi, Shirin, et al.
(författare)
-
Grazing-Incidence Small Angle Neutron Scattering from Structures below an Interface
- 2017
-
Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 50:4, s. 1066-1074
-
Tidskriftsartikel (refereegranskat)abstract
- Changes of scattering are observed as the grazing angle of incidence of an incoming beam increases and probes different depths in samples. A model has been developed to describe the observed intensity in grazing incidence small angle neutron scattering (GISANS) experiments. This includes the significant effects of instrument resolution, the sample transmission, which depends on both absorption and scattering, as well as the sample structure. The calculations are tested with self-organised structures of two colloidal samples with different size particles that were measured on two different instruments. The model allows calculations for various instruments with defined resolution and can be used to design future improved experiments. The possibilities and limits of GISANS for different studies are discussed using the model calculations.
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| 45. |
- Nouhi, Shirin, et al.
(författare)
-
Sticking particles to solid surfaces using Moringa oleifera proteins as a glue
- 2018
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 168, s. 68-75
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental studies have been made to test the idea that seed proteins from Moringa oleifera which are novel, natural flocculating agents for many particles could be used to promote adhesion at planar interfaces and hence provide routes to useful nanostructures. The proteins bind irreversibly to silica interfaces. Surfaces that had been exposed to protein solutions and rinsed were then exposed to dispersions of sulfonated polystyrene latex. Atomic force microscopy was used to count particle density and identified that the sticking probability was close to 1. Measurements with a quartz crystal microbalance confirmed the adhesion and indicated that repeated exposures to solutions of Moringa seed protein and particles increased the coverage. Neutron reflectivity and scattering experiments indicate that particles bind as a monolayer. The various results show that the 2S albumin seed protein can be used to fix particles at interfaces and suggest routes for future developments in making active filters or improved interfaces for photonic devices.
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| 46. |
- Nouhi, Shirin, 1987-
(författare)
-
Structure formation at solid/liquid interfaces : Understanding self-assembly and environmental challenges
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work described in the present dissertation has explored the structure of particles and molecules at solid/liquid interfaces, aiming to understand the physics of self-organizing systems and use this knowledge to address some environmental issues. Surface-sensitive neutron scattering techniques, such as reflectometry and grazing incidence small angle scattering, have been used as the primary tool to investigate structures in proximity to an interface. Some of the challenges in the interpretation of neutron scattering data are discussed, and new methods for analyzing the signal have been proposed.It was shown that charged stabilized colloidal particles can self-assemble and form large areas (20 cm2) of crystalline structures, close to a smooth solid surface extending to depths of several micrometers, while orienting themselves into smaller crystallites in the bulk of the suspension. The adsorption of proteins from the seeds of different species of Moringa trees on alumina, silica and polystyrene surfaces was studied, as a means for using proteins from different sources and with different properties, for the water clarification step in the purification process. The seed proteins also showed to enable locking the structure of colloidal particles at the solid/liquid interface, acting as a molecular glue.Perfluorinated surfactants (PFASs), widely used in industrial, pharmaceutical and food packing products, have been identified as emerging pollutants, raising a global concern for the environment and wildlife. The present study has shown how PFASs molecules of different fluorocarbon chain length and with different functional groups, create defects in model membranes by partitioning and removing phospholipids from the bilayer, making the bilayer thin and less dense.The effect of interface roughness was studied on the lamellar structure of a non-ionic surfactant. Concentrated solutions of the surfactant have been shown to form well-ordered and well-aligned structures at a smooth interface, which could be modified further by simply heating the sample. However it was found that even small roughness, of the same order as the bilayer thickness, can distort the structure to a depth of several micrometers from the interface. Heating the sample could improve the alignment but not as much as that formed at a smooth surface.
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| 47. |
- Nylander, Tommy, et al.
(författare)
-
Neutron Reflectometry to Investigate the Delivery of Lipids and DNA to Interfaces
- 2008
-
Ingår i: Biointerphases. - : American Vacuum Society. - 1559-4106 .- 1934-8630. ; 3:2, s. FB64-FB82
-
Forskningsöversikt (refereegranskat)abstract
- The application of scattering methods in the study of biological and biomedical problems is a field of research that is currently experiencing fast growth. In particular, neutron reflectometry (NR) is a technique that is becoming progressively more widespread, as indicated by the current commissioning of several new reflectometers worldwide. NR is valuable for the characterization of biomolecules at interfaces due to its capability to provide quantitative structural and compositional information on relevant molecular length scales. Recent years have seen an increasing number of applications of NR to problems related to drug and gene delivery. We start our review by summarizing the experimental methodology of the technique with reference to the description of biological liquid interfaces. Various methods for the interpretation of data are then discussed, including a new approach based on the lattice mean-field theory to help characterize stimulus-responsive surfaces relevant to drug delivery function. Recent progress in the subject area is reviewed in terms of NR studies relevant to the delivery of lipids and DNA to surfaces. Lastly, we discuss two case studies to exemplify practical features of NR that are exploited in combination with complementary techniques. The first case concerns the interactions of lipid-based cubic phase nanoparticles with model membranes (a drug delivery application), and the second case concerns DNA compaction at surfaces and in the bulk solution (a gene delivery application).
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| 48. |
- Oleshkevych, Anna, et al.
(författare)
-
Thermally driven redistribution of phases and components in Cu/Sn thin films
- 2012
-
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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| 49. |
- Olsmats, Eleonora, et al.
(författare)
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Pea protein [Pisum sativum] as stabilizer for oil/water emulsions
- 2024
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier. - 0001-8686 .- 1873-3727. ; 326
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Tidskriftsartikel (refereegranskat)abstract
- A map of stability for various water/oil/pea protein compositions has been plotted from the numerous reported results. Two clear regions of stability were identified. High internal oil phase emulsions with 70–80%, v/v oil content stabilized by total pea protein concentration <2.5%, w/v showed stability. Low oil content of 10–30%, v/v for a range of total pea protein concentrations >0.5%, w/v have also been identified as stable. Intermediate oil content and pea protein concentrations >4% w/v are unexplored regions and are likely to be areas of fruitful future research. The wide range of stability suggests that different stabilization mechanisms could be important for different compositions and careful consideration has to be taken to avoid oversimplification. Both stabilization with particles, i.e. Pickering emulsions, and protein unfolding have been suggested as mechanisms. The diverse way of describing stability makes it difficult to intercompare results in different studies. A summary of different oil types used have been presented and several properties such as dynamic viscosity, density, the dielectric constant and interfacial tension have been summarized for common vegetable oils. The type of vegetable oil and emulsion preparation techniques were seen to have rather little effect on emulsion stability. However, the different extraction methods and processing of the pea material had more effect, which could be attributed to changing composition of different proteins and to the states of aggregation and denaturing. Careful consideration has to be taken in the choice of extraction method and an increased understanding of what contributes to the stability is desirable for further progress in research and eventual product formulation.
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| 50. |
- 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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