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Adsorption and Ordering of Surface Active Molecules and Particles at Solid Interfaces and in the Bulk
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 915
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-171739ISBN: 978-91-554-8327-2 (print)OAI: oai:DiVA.org:uu-171739DiVA: diva2:512536
Public defence
2012-05-16, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2012-04-24 Created: 2012-03-27 Last updated: 2012-08-01Bibliographically approved
List of papers
1. Effect of Concentration and Addition of Ions on the Adsorption of Aerosol-OT to Sapphire
Open this publication in new window or tab >>Effect of Concentration and Addition of Ions on the Adsorption of Aerosol-OT to Sapphire
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 18, 14567-14573 p.Article in journal (Refereed) Published
Abstract [en]

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

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-134827 (URN)10.1021/la101969p (DOI)000281690600030 ()
Available from: 2010-12-02 Created: 2010-12-01 Last updated: 2012-08-01Bibliographically approved
2. Adsorption of Aerosol-OT to Sapphire: Lamellar Structures Studied with Neutrons
Open this publication in new window or tab >>Adsorption of Aerosol-OT to Sapphire: Lamellar Structures Studied with Neutrons
2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 8, 4669-4678 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-152837 (URN)10.1021/la1048985 (DOI)000289321000053 ()
Available from: 2011-05-02 Created: 2011-05-02 Last updated: 2017-12-11Bibliographically approved
3. Structure of a large colloidal crystal: controlling orientation and three-dimensional order
Open this publication in new window or tab >>Structure of a large colloidal crystal: controlling orientation and three-dimensional order
2012 (English)In: RSC Advances, ISSN 2046-2069, Vol. 2, no 18, 7091-7098 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-171737 (URN)10.1039/c2ra21092d (DOI)000306946500014 ()
Note

Original manucript title: Structure of colloidal crystal : controlling size and three-dimensional order

Available from: 2012-03-26 Created: 2012-03-26 Last updated: 2012-10-02Bibliographically approved
4. Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
Open this publication in new window or tab >>Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
Show others...
2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 22, 221601- p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-171738 (URN)10.1063/1.4723634 (DOI)000304823800012 ()
Available from: 2012-03-26 Created: 2012-03-26 Last updated: 2017-12-07Bibliographically approved
5. Adsorption of a Water Treatment Protein from Moringa oleifera Seeds to a Silicon Oxide Surface Studied by Neutron Reflection
Open this publication in new window or tab >>Adsorption of a Water Treatment Protein from Moringa oleifera Seeds to a Silicon Oxide Surface Studied by Neutron Reflection
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 6, 3902-3910 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Biological Sciences Physical Sciences
Identifiers
urn:nbn:se:uu:diva-135431 (URN)10.1021/la9031046 (DOI)000275226700025 ()20163083 (PubMedID)
Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2012-08-01Bibliographically approved

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