Dokument: Untersuchung des Aggregationsverhaltens von Tensiden an festen Oberflächen mittels hochauflösender TIRF-Mikroskopie

Titel:	Untersuchung des Aggregationsverhaltens von Tensiden an festen Oberflächen mittels hochauflösender TIRF-Mikroskopie
Weiterer Titel:	Analysis of the aggregation behavior of surfactants on solid surfaces via high-resolution TIRF-microscopy
URL für Lesezeichen:	https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=61134
URN (NBN):	urn:nbn:de:hbz:061-20221107-114942-3
Kollektion:	Dissertationen
Sprache:	Deutsch
Dokumententyp:	Wissenschaftliche Abschlussarbeiten » Dissertation
Medientyp:	Text
Autor:	Bous, Maria Johanna [Autor]
Dateien:	[Dateien anzeigen] Adobe PDF [Details] 14,79 MB in einer Datei [ZIP-Datei erzeugen] Dateien vom 07.11.2022 / geändert 07.11.2022
Beitragende:	Prof. Dr. von Rybinski, Wolfgang [Gutachter] Prof. Dr. Seidel, Claus [Gutachter]
Stichwörter:	hochauflösende TIRF-Mikroskopie, Tenside, Aggregationsverhalten, Oberflächenaggregate, AFM, Oberflächenspannung, PE10500, CTAB, Nilrot
Dewey Dezimal-Klassifikation:	500 Naturwissenschaften und Mathematik » 540 Chemie
Beschreibungen:	In der vorliegenden Arbeit wurde der Aufbau der Adsorptionsschicht sowie der Adsorptionsprozess verschiedener selbstassoziierender Tenside an hydrophilen und hydrophoben Oberflächen mithilfe der TIR-Fluoreszenzmikroskopie untersucht. Die Fluoreszenzmikroskop-Bilder wurden zudem mit dem PAINT-Bildverarbeitungsverfahren aufbereitet, um hochaufgelöste Bilder und Informationen zu Aufbau und zeitlichen Veränderung der Adsorptionsschicht zu erhalten. Ziel der Arbeit war es, den Aggregationsprozess von Tensiden an verschiedenen Oberflächen durch die Kombination verschiedener Methoden möglichst detailliert aufzuklären und die Möglichkeiten der TIRF-Mikroskopie sowie PAINT-Methode zur Untersuchung von Tensidaggregaten zu erfassen. Mittels umgebungssensitiven Farbstoffs gelang die Visualisierung der hydrophoben Domänen von PE10500-Aggregaten an hydrophobiertem Glas oder einer CTAB-Schicht an Glas mit der TIRF-Mikroskopie. Die bereits anhand von Adsorptionsisothermen gefundene Zunahme von PE10500-Aggregatgrößen oder aber auch Verdichtung der Oberfläche mit Aggregaten konnte detaillierter charakterisiert werden. Die Helligkeit der Fluoreszenzereignisse der TIRF-M-Bilder lässt sowohl auf eine Zunahme der Hydrophobie einzelner Aggregate mit zunehmender Tensidkonzentration als auch auf eine Zunahme der Anzahl hydrophober Domänen schließen. Mithilfe der PAINT-Analyse konnten PAINT-Bilder dieser separaten, runden hydrophoben Domänen von PE10500-Aggregaten erstellt werden. Zudem konnte durch Untersuchung der Trefferdichteverteilung nachgewiesen werden, dass die visualisierten hydrophoben Domänen aus adsorbierten Tensidmolekülen in Wechselwirkung mit den Alkylketten der Silanschicht bestehen. Die Auswertung der Länge der Fluoureszenzsignal-Spur zeigte, dass die meisten hydrophoben Domänen nur sehr kurzzeitig zu beobachten sind, d.h. sie sind aufgrund des Verteilungsgleichgewichts von Tensidmolekülen zwischen adsorbierten und in Lösung befindlichen Spezies und aufgrund der Brown'schen Kettenbewegung adsorbierter Moleküle starken räumlichen und zeitlichen Veränderungen unterworfen. Die PAINT-Methode eignet sich zur Größenabschätzung im Bereich 13-60 nm. Sie bietet neben der Erstellung hochaufgelöster Bilder die Möglichkeit, Informationen über zeitliche Veränderungen einer Adsorptionsschicht bzw. die Wechselwirkung von Aggregaten mit der Oberfläche zu erhalten. Anders als bei AFM oder cryo-TEM liegt der Fokus der TIRF-Mikroskopie und PAINT-Auswertung weniger auf der geometrischen Abbildung von Adsorptionsschichten, sondern der Untersuchung der Wechselwirkung der Moleküle in der Adsorptionsschicht mit Oberfläche und Farbstoffmolekülen und der Erfassung lokaler Heterogenitäten unter natürlichen Bedingungen. In this work the structure of the adsorption layer and the adsorption process of different surfactants at both hydrophilic and hydrophobic surfaces were investigated via TIR-fluorescence microscopy. In addition, for selected adsorption systems the fluorescence microscope images were post-processed using the PAINT-method. This produced super-resolved images from which information on temporal changes of the adsorption layer was derived. The aim of this work was to examine the aggregation process of surfactants at different surfaces and to explore the potential of the PAINT-method regarding the study of surfactant aggregates. A total internal reflection fluorescence microscope (TIRF-M) was used to study the adsorption process at the water-solid-interface. The dye 'nile red' was added to visualize hydrophobic domains of surfactant aggregates by means of fluorescence. For the first time, the PAINT-method was applied to non-fixed, self-associated structures. The applicability of the PAINT-method on surfactant systems was evaluated using the well-studied system of lipid vesicles on glass. So far, the PAINT-method was applied to locally fixed probes which did not move or change in size or shape during the exposure time. By microscoping self-assembling surfactant structures the underlying dynamic structural and time dependent changes due to equilibrium states between different locations of surfactant molecules could be studied. This also includes dynamics of adsorption processes. Different adsorption layer types of surfactants could be visualized via TIRF-microscopy. At relatively plane and hydrophilic glass surfaces both separate surfactant aggregates and more continuous hydrophobic areas in CTAB-adsorption layers could be detected. From the adsorption isotherm, a Langmuir-like adsorption of CTAB at silica gel could be deduced, whereas by TIRF-microscopy images a random aggregation of adsorbed surfactant molecules could be verified. Changes in the adsorption layer by addition of other surfactants could be instantly visualized. For example, the addition of nonionic PE10500 resulted in dissolving of the homogenous CTAB-layer and the addition of C12EO7 in the formation of mixed aggregates. As expected from published data on the interaction between PE10500 and deprotonated glass surfaces, no fluorescence of nile red in the PE10500 solution on glass could be detected, even above cmc. However, on mica aggregates of only a few molecules could be visualized using atomic force microscopy. This means that PE10500-aggregates on glass consist of highly coiled surfactants which form small, poorly hydrophobic domains that weakly interact with nile red. From the adsorption isotherm the beginning of the aggregation process of PE10500 on hydrophobic silicagel well below the cmc could be deduced. At this concentration also separate PE10500-aggregates on hydrophobized glass could be visualized in TIRF-M-images. The analysis of brightness of these images showed an increase of both brightness and number of fluorescent objects with increasing surfactant concentration. This means there is a correlation between surfactant concentration and hydrophobicity and aggregate density. Super-resolved synthetic images of PE10500-aggregates on a hydrophobic surface could be generated from TIRF-M-images using the PAINT-method. These PAINT-images showed round shaped fluorescent objects in a 2d-projection. The PAINT-method is suitable for a size estimate of objects in the range of 13 to 60 nm. From the localization density analysis of the PAINT-images could be concluded that the hydrophobic domains visualized by nile red consist of both aggregated PE10500 and the alkyl chains of the silane layer (glass modification). Here, the interaction of surfactant with the surface due to chemical properties could be proved. The number of generated PAINT-objects did not rise abruptly at the cmc but increased significantly at concentrations 5-times above cmc. This evidences a participation of micelles in the adsorption process well above the cmc. From a mean square displacement analysis it could be concluded that there is no movement of surfactant aggregates in the range of 10 nm during the exposure time of 8-50 ms. So if micelles adsorb on the surface, they strongly interact with the silane layer without changing their position along the surface. At different CTAB-concentrations an establishment of equilibrium between adsorbed surfactant and CTAB in solution within minutes could be deduced from a brightness analysis of TIRF-M-images. The temporal limitation of a detected fluorescence trajectory proves that the CTAB-adsorption layer is dynamically changing due to Brownian motion of surfactant chain segments. A diffusion trajectory analysis of nile red in a CTAB-adsorption layer on glass showed that the dye diffusion is highly locally confined at 0.1-times cmc and more spacious at 11-times cmc. So the adsorption process begins with defined surface aggregates which merge and form connected domains with increasing surfactant concentration. For example, by adding 0.3-times cmc nonionic C12EO7-surfactant to a CTAB-solution (> cmc) PAINT-derived dye localization showed a more spacious diffusion than in a pure CTAB-layer, though TIRF-M-images did not show significant changes. This means that these mixed surfactant aggregates are less densely packed than CTAB-aggregates. Also, the detected fluorescence trajectory of nile red in PE10500-domains are temporally limited, proving dynamic changes in PE10500-aggregates on hydrophobized glass. The distribution of these observation durations suggests that most PE10500-PAINT-objects emit fluorescence with a total duration of less than 2.5 s. So like CTAB-aggregates, also PE10500-aggregates are dynamically changing due to Brownian motion of surfactant molecules and due to the equilibrium of distribution of PE10500 adsorbed to the surface and in solution. Different stages of the build-up of surfactant adsorption layers could be visualized on hydrophilic and hydrophobic surfaces using TIRF-microscopy. The interaction between surfactant molecules and the surface could be verified and the hydrophobicity of aggregates could be analyzed. The PAINT-method proved to be suitable for generating super-resolved images of hydrophobic domains, visualization of local heterogeneity in adsorption layers, analysis of temporal changes in packing density and local dimensions of adsorbed surfactant-domains and for analysis of interaction between surfactant and surface. By visualizing hydrophobic domains due to chemical properties of the adsorption layer the method used in this work sets itself apart from other super-resolution imaging techniques like AFM and cryo-TEM, which are based on imaging geometrical shapes.
Lizenz:	Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz
Fachbereich / Einrichtung:	Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie » Physikalische Chemie und Elektrochemie
Dokument erstellt am:	07.11.2022
Dateien geändert am:	07.11.2022
Promotionsantrag am:	04.05.2021
Datum der Promotion:	07.03.2022