| 1. |
- Hellsing, Maja, et al.
(författare)
-
Adsorption of Aerosol-OT to Sapphire : Lamellar Structures Studied with Neutrons
- 2011
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:8, s. 4669-4678
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of sodium bis 2-ethylhexyl sulfosuccinate, NaAOT, to a sapphire surface from aqueous solution has been studied by neutron reflection at concentrations above the critical micelle concentration (cmc). Complementary measurements of the bulk structure were made with small-angle neutron scattering and grazing incidence small-angle neutron scattering. At a concentration of about 1% wt (10 X cmc), lamellar phase NaAOT was observed both at the surface and in the bulk. The structure seen at the interface for a solution of 2% wt NaAOT is a 35 +/- 2 angstrom thick bilayer adsorbed to the sapphire surface at maximum packing density, followed by an aligned stack of fluctuating bilayers of thickness 51 +/- 2 angstrom and with an area per molecule of 40 +/- 2 angstrom(2). Each bilayer is separated by a water: at 25 degrees C, this layer is 148 +/- 2 angstrom. A simple model for the reflectivity from fluctuating layers is presented, and for 2.0% wt NaAOT the fluctuations were found to have an amplitude of 25 +/- 5 angstrom. The temperature sensitivity of the structure at the surface was investigated in the range 15-30 degrees C. The effect of temperature was pronounced, with the solvent layer becoming thinner and the volume occupied by the NaAOT molecules in a bilayer increasing with temperature. The amplitude of the fluctuations, however, is approximately temperature independent in this range. The adsorption of NaAOT at the sapphire surface resembles that previously found at hydrophilic and hydrophobic silica surfaces. The coexisting bulk lamellar phase has a spacing of layers similar to that observed at the surface. These observations are an indication that the major driving force for adsorption is self-assembly, independent of the chemical nature of the interface.
|
|
| 2. |
- Hellsing, Maja S., 1975-
(författare)
-
Adsorption and Ordering of Surface Active Molecules and Particles at Solid Interfaces and in the Bulk
- 2012
-
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.
|
|
| 3. |
- 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-
-
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.
|
|
| 4. |
- Hellsing, Maja S., et al.
(författare)
-
Effect of Concentration and Addition of Ions on the Adsorption of Aerosol-OT to Sapphire
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:18, s. 14567-14573
-
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
|
|
| 5. |
- Hellsing, Maja S., et al.
(författare)
-
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.
|
|
| 6. |
- Hellsing, Maja S., et al.
(författare)
-
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
-
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.
|
|
| 7. |
- Hellsing, Maja S., et al.
(författare)
-
Structure of flocs of latex particles formed by addition of protein from Moringa seeds
- 2014
-
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.
|
|
| 8. |
- Kwaambwa, Habauka M., et al.
(författare)
-
Adsorption of a Water Treatment Protein from Moringa oleifera Seeds to a Silicon Oxide Surface Studied by Neutron Reflection
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:6, s. 3902-3910
-
Tidskriftsartikel (refereegranskat)abstract
- An extract from the seeds of the Moringa oleifera tree that is principally a low molecular mass protein is known to be efficient as a coagulating agent for water treatment. The present paper investigates the adsorption of the purified protein to silica interfaces in order to elucidate the mechanism of its function as a flocculent. Neutron reflection permits the determination of the structure and composition of interfacial layers at the solid/solution interface. Dense layers of protein with about 5.5 mg m(-2) were found at concentrations above 0.025% wt. The overall thickness with a dense layer in excess of 60 angstrom at 0.05 wt % suggests strong co-operative binding rather than single isolated molecules. All ionic surfactant, sodium dodecyl sulfate, was also seen to coadsorb. This strong adsorption of protein in combination with the tendency for the protein to associate suggests a mechanism for destabilizing particulate dispersions to provide filterable water. This call occur even for the protein that has previously been identified as being of low mass (about 7 kDaltons) and thus is unlikely to be efficient in bridging or depletion flocculation.
|
|
| 9. |
- Olsson, Anders, et al.
(författare)
-
A holder to rotate sample cells to avoid sedimentation in small-angle neutron scattering and ultra small-angle neutron scattering experiments
- 2013
-
Ingår i: Measurement science and technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 24:10, s. 105901-
-
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.
|
|
| 10. |
- Rennie, Adrian R., et al.
(författare)
-
Learning about SANS instruments and data reduction from round robin measurements on samples of polystyrene latex
- 2013
-
Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 46:5, s. 1289-1297
-
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.
|
|
