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Structure formation at solid/liquid interfaces: Understanding self-assembly and environmental challenges
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.ORCID iD: 0000-0002-5203-8057
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 64
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1732
Keywords [en]
Solid/liquid interface, neutron scattering, colloidal particles, self-assembly, perfluoroalkyl substance, Moringa seed proteins, adsorption, lamellar disorder, thermal fluctuations.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-362075ISBN: 978-91-513-0475-5 (print)OAI: oai:DiVA.org:uu-362075DiVA, id: diva2:1255624
Public defence
2018-12-14, Å80127, Ångströmlaboratoriet, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2018-11-19 Created: 2018-10-13 Last updated: 2018-11-30
List of papers
1. Comparative study of flocculation and adsorption behavior of Moringa peregrina and Moringa oleifera seed proteins for water treatment
Open this publication in new window or tab >>Comparative study of flocculation and adsorption behavior of Moringa peregrina and Moringa oleifera seed proteins for water treatment
(English)In: Article in journal (Refereed) Submitted
National Category
Earth and Related Environmental Sciences Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-362073 (URN)
Available from: 2018-09-30 Created: 2018-09-30 Last updated: 2018-10-17Bibliographically approved
2. Grazing-Incidence Small Angle Neutron Scattering from Structures below an Interface
Open this publication in new window or tab >>Grazing-Incidence Small Angle Neutron Scattering from Structures below an Interface
2017 (English)In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 50, no 4, p. 1066-1074Article in journal (Refereed) Published
Abstract [en]

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. 

Keywords
GISANS, Solid/liquid interface, colloidal particles
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-322577 (URN)10.1107/S1600576717007518 (DOI)000407040700011 ()28808432 (PubMedID)
Funder
Swedish Research Council, 621-2012-4382
Available from: 2017-05-26 Created: 2017-05-26 Last updated: 2018-10-13Bibliographically approved
3. Sticking particles to solid surfaces using Moringa oleifera proteins as a glue
Open this publication in new window or tab >>Sticking particles to solid surfaces using Moringa oleifera proteins as a glue
Show others...
2018 (English)In: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 168, p. 68-75Article in journal (Refereed) In press
Abstract [en]

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.

National Category
Physical Chemistry Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-338407 (URN)10.1016/j.colsurfb.2018.01.004 (DOI)000443630200010 ()29373240 (PubMedID)
Funder
Swedish Research Council, 348-2011-7241Swedish Research Council, 621-2012-4382
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2018-11-01Bibliographically approved
4. Interactions of perfluoroalkyl substances with a phospholipid bilayer studied by neutron reflectometry
Open this publication in new window or tab >>Interactions of perfluoroalkyl substances with a phospholipid bilayer studied by neutron reflectometry
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2017 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 511, p. 474-481Article in journal (Refereed) Published
Abstract [en]

The interactions between perfluoroalkyl substances (PFASs) and a phospholipid bilayer (1,2-dimyristoyl-sn-glycero-3-phosphocholine) were investigated at the molecular level using neutron reflectometry. Representative PFASs with different chain length and functional groups were selected in this study including: perfluorobutane sulfonate (PFBS), perfluorohexanoate (PFHxA), perfluorohexane sulfonate (PFHxS), perfluorononanoate (PFNA), perfluorooctane sulfonate (PFOS), and perfluorooctane sulfonamide (FOSA). All PFASs were found to interact with the bilayer by incorporation, indicating PFAS ability to accumulate once ingested or taken up by organisms. The interactions were observed to increase with chain length and vary with the functional group as SO2NH2" role="presentation">(FOSA) > SO2O−" role="presentation">(PFOS) > COO(PFNA). The PFAS hydrophobicity, which is strongly correlated with perfluorocarbon chain length, was found to strongly influence the interactions. Longer chain PFASs showed higher tendency to penetrate into the bilayer compared to the short-chain compounds. The incorporated PFASs could for all substances but one (PFNA) be removed from the lipid membrane by gentle rinsing with water (2 mL min−1). Although short-chain PFASs have been suggested to be the potentially less bioaccumulative alternative, we found that in high enough concentrations they can also disturb the bilayer. The roughness and disorder of the bilayer was observed to increase as the concentration of PFASs increased (in particular for the high concentrations of short-chain substances i.e. PFHxA and PFBS), which can be an indication of aggregation of PFASs in the bilayer.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-330505 (URN)10.1016/j.jcis.2017.09.102 (DOI)000417008200053 ()29073553 (PubMedID)
Funder
Swedish Research Council, 621-2012-4382Swedish Research Council, 2015-03938
Available from: 2017-10-02 Created: 2017-10-02 Last updated: 2018-10-13Bibliographically approved
5. Distortion of surfactant lamellar phases induced by surface roughness
Open this publication in new window or tab >>Distortion of surfactant lamellar phases induced by surface roughness
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

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

Keywords
Roughness, thermal fluctuations, disorder, neutron reflectometry, nonionic surfactant
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-363134 (URN)
Available from: 2018-10-13 Created: 2018-10-13 Last updated: 2018-10-17Bibliographically approved

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