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Dissertations / Theses on the topic 'Air – water interfaces'

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Published: 4 June 2021
Last updated: 2 February 2022

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1

Roland, Christopher. "Phase transitions of phospholipid monolayers on air-water interfaces." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66032.

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2

Knock, Mona Marie. "Monolayers of cationic surfactants at the air-water and oil-water interfaces." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:c0cdaf66-716a-4b48-b22c-659d1fe2a342.

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Monolayers of the cationic surfactant hexadecyltrimethylammonium halide (CTAX, where X = F¯, Cl¯, Br¯, and I¯) have been studied at the air-water and oilwater interfaces. At the air-water interface, the effects of the halide counterion and the addition of counterion were investigated. Sum-frequency spectroscopy (SFS), ellipsometry, and surface tensiometry indicated that the counterion changed the efficiency and effectiveness of the surfactant, both decreasing in the order of Br¯> Cl¯>F¯. The addition of salt in the form of 0.1 M KX was found to reduce the cmc but had little effect on the limiting area per molecule attained at the cmc, which increased from 44 Å2 for CTAB to 65 Å2 for CTAC and ca. 94 Å2 for CTAF. Neither SFS nor ellipsometry provided any firm evidence for specific effects of the halide ions on the structure of the surfactant monolayers. For CTAB monolayers in the absence of excess electrolyte, the effect of area per molecule on the sum-frequency (SF) spectra was studied. Mixed monolayers of CTAB and tetradecane at the air-water interface exhibit a first-order phase transition from a conformationally disordered to a conformationally ordered state as the temperature is lowered. The phase transition occurs ca. 11 °C above the bulk melting point of tetradecane. A new experimental arrangement is described for acquiring SF spectra from surfactants at the oil-water interface. The key features of this approach are the stabilisation of a thin oil film between a sapphire prism and an aqueous phase, and the use of total internal reflection to enhance the total signal and discriminate against signals from other interfaces in the system. With this new methodology, the first SF vibrational spectra of surfactant monolayers at an alkane-water interface were obtained. Surface tensiometry was used to characterise the monolayers further. The structure of CTAB monolayers at the hexadecane-water interface was determined by SFS and compared with monolayers of CTAB at the air-water interface. At low concentrations, CTAB/hexadecane showed the expected features in the C-H stretching region, characteristic of a conformationally disordered monolayer. As the bulk concentration approached the critical micelle concentration, the spectra changed to one characteristic of a more ordered, upright conformation. Ellipsometric measurements supported this conclusion. This qualitative structural change is not observed in analogous monolayers at the air-water interface or CCl4-water interface, or in surfactant solutions in contact with a hydrophobic solid surface.
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3

Boudala, Faisal S. "Mercury flux measurements across air/water and air/soil interfaces at Kejimkujik National Park." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0028/MQ36400.pdf.

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4

Casillas-Ituarte, Nadia Ninel. "Spectroscopic Studies of Atmospheric Relevant Air-Aqueous and Air-Silica Interfaces." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268155570.

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5

Bell, Graham Ronald. "Sum-frequency spectroscopy of surfactant monolayers at the air-water and oil-water interfaces." Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.600035.

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In order to improve understanding of the relationship between molecular structure and interfacial structure, surfactant monolayers at the air-water (A-W) and oil-water (O-W) interfaces, and counterions bound to surfactant monolayers, have been studied using sum-frequency spectroscopy (SFS) and complementary techniques, including neutron reflection (NR) and ellipsometry. The non-linear optical technique of SFS is applied first to the study of surfactants at the A-W interface. Various theoretical models used to explain peak intensities in the resulting vibrational spectra are critically assessed. Values of mean tilt and degree of conformational disorder of adsorbed surfactant molecules are inferred. It is observed that the molecular conformation of monolayers of different surfactants cannot be predicted solely from the area per hydrocarbon chain, depending also on the nature of the head-group. At constant area per molecule, monolayer structure is found to be unaffected by chain length. The behaviour of binary mixtures of a non-ionic and an anionic or zwitterionic surfactant is found to be indicative of ideal mixing thermodynamically in the monolayer, whereas strong synergistic interactions are observed for an anionic-zwitterionic mixture. Two counterions known to induce viscoelasticity in surfactant solutions are then investigated. The orientations of benzoate and p-tosylate ions bound to surfactant monolayers at the A-W interface are quantified. Both are found to be located deep within the hydrophobic region of the monolayer. The presence of p-tosylate causes structural changes in the monolayer, and p-tosylate is found to be acting as both ion and cosurfactant. Specifically, through the joint application of SFS and NR, the structure of a monolayer of hexadecyltrimethylammonium p-tosylate is established, revealing that the hydrocarbon chains of the surfactant rise steeply away from the water before turning over to lie flatter in the region above the p-tosylate ions. These findings are related to micelles in solution to provide an insight into the sphere-to-rod transitions thought to be responsible for dramatic changes in the physical properties of surfactant solutions in the presence of specific counterions. Finally, an entirely new experimental arrangement is developed to address the significant technical problems standing in the way of obtaining SF spectra of surfactants adsorbed at the O-W interface. The same basic design was later used to acquire the first SF spectra of surfactant monolayers at this interface.
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6

Villa, Stefano. "Behaviour of a Colloid close to an Air-Water Interface : Interactions and Dynamics." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS074/document.

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Malgré un rôle important en physique, biologie et dans les processus industriels tels l’agroalimentaire et la dépollution de l’eau, la dynamique d'une particule colloïdale à proximité d'une interface fluide et ses interactions avec l’interface sont des phénomènes physiques encore débattus.Dans cette thèse, nous explorons la dynamique et l'interaction de particules colloïdales individuelles à proximité d'une interface air-eau à l’équilibre thermique.Afin de mener cette étude sans perturber le système expérimental, nous avons conçu et construit un microscope interférentiel à double onde adapté à l'interface air-eau. Contrairement à d'autres techniques expérimentales, notre configuration permet la mesure précise de la distance absolue entre particule l'interface sans nécessiter d’étalonnage ou d’hypothèse sur l'emplacement de l'interface. Nous avons ainsi pu obtenir des trajectoires hautement résolues de particules en 3D proches de l'interface, permettant la mesure précise des diffusions proche de l’interface et des interactions particules-interface.Le système montre deux profils d’énergie potentielle différents. Deux distances d’équilibre particule-interface sont ainsi observées. La plus grande peut être expliquée par la compétition des interactions de Van der Waals et électrostatiques avec la pesanteur. La distance d’équilibre plus courte ne peut s’expliquer que par la présence d’une interaction attractive supplémentaire. Les origines possibles de cette interaction sont discutées.En utilisant une nouvelle méthode d'analyse des déplacements quadratiques moyens des particules dans un potentiel générique, nous avons pu accéder aux coefficients de friction visqueuse des particules en fonction de la distance à l'interface. De manière singulière, l’interface air-eau se comporte comme une paroi liquide pour le mouvement des particules parallèlement à l’interface et comme une paroi solide pour le mouvement des particules perpendiculaire à l’interface. Ce résultat expérimental peut être partiellement rationalisé en considérant des modèles récents basés sur l’incompressibilité de surface. Cependant, certaines différences entre les expériences et les théories demeurent. Les coefficients de friction visqueuse sont plus importants que les prédictions hydrodynamiques et dépendent de la charge électrique des particules, ce qui suggère un possible rôle des phénomènes électrocinétiques.Enfin, le piégeage des particules à l'interface air-eau et leur angle de contact ont été mesurés tout en modifiant la force ionique de la solution aqueuse et en faisant varier l‘état de surface des colloïdes
Despite the relevance to environmental, biological and industrial processes, the motion of a colloidal particle close to a fluid interface and the way it interacts with the water surface are still largely elusive and intriguing physical phenomena.In this thesis, we explore the motion dynamics and the interaction of individual colloidal particles close to an air-water interface in thermal equilibrium.In order to investigate them without perturbing or altering the experimental system, we designed and built a dual-wave reflection interference microscope working with an air-water interface geometry. Contrary to other established experimental techniques, our set-up allows accurate measurements of the absolute particle-interface distance and thus does not require any calibration or assumption to know the location of the interface. Highly resolved 3D particle trajectories close to the interface were obtained, from which information on particle diffusion close to the interface and particle-interface interactions are obtained.The system shows two different potential energy landscapes resulting in two different equilibrium particle-interface distances. The larger one can be fairly explained by Van der Waals and electrostatic interactions combined with gravity. The shorter one highlights the existence of an unexpected additional attractive interaction. The possible origins of such an interaction are discussed.Using a method of analysis of the particle mean square displacements in a generic potential we developed, we were able to access to particle drag coefficients as a function of the distance from the interface. Peculiarly, the air-water interface acts as a slip boundary for the particle motion parallel to the interface and as a no-slip boundary for the particle motion perpendicular to the interface. This experimental result can be partially rationalized considering recent models based on surface incompressibility. However, some discrepancies between experiments and theories remain. Experimental drag coefficients are larger than the hydrodynamic predictions and depend on the particle electrical charge, pointing therefore to a possible role of electrokinetic phenomena.Finally, the particle trapping at the air-water interface and its contact angle were observed while tuning the ionic strength of the aqueous solution and varying the surface state of the colloids
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7

Moglianetti, Mauro. "Polymer surfactant mixtures confined at the air/water and solid/waste interfaces." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504920.

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8

Crichton, Donna. "The interaction of oils with surfactant monolayers at the air-water surface." Thesis, University of Hull, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310247.

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9

Castada, Hardy Zingalaoa. "Brewster Angle Microscopy Study of Model Lung Surfactant Systems at the Air-Water and Air-Physiological Buffer Interfaces." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1281642097.

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10

Zang, Duyang. "The dynamics of interfaces : rheology of silica nanoparticle monolayers at the air-water interface and dendritic growth in multicomponent alloys." Paris 11, 2009. http://www.theses.fr/2009PA112145.

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Cette thèse présente les deux sujets liés à la dynamique d'interfaces: la rhéologie des particules monocouches et de la croissance dendritique des alliages. Dans la première partie, chapitre1-6, les propriétés des monocouches de nanoparticules de silice à l’interface air-eau sont présentées et reliées à la stabilité des mousses faites avec les dispersions aqueuses de ces particules. Les propriétés des couches: évolution de texture, pression de surface, épaisseur, angle de contact des particules et concentration de surface sont caractérisées pour différentes hydrophobicités des particules. La viscoélasticité de compression des couches a été déterminée par trois méthodes basées sur l’utilisation de deux plaques de Wilhelmy dans des cuves Langmuir. Les différences remarquables entre les couches comprimées et les couches déposées ont été trouvés. Les modules présentent un maximum à l'hydrophobicité intermédiaire des particules et dépendent de la vitesse de déformation, de la quantité de particule initiale, de la longueur de la cuve et de l'âge de la couche. La viscoélasticité de cisaillement des couches a été également déterminée. Une analogie fréquence-gradient de vitesse a été trouvée comme chez d’autres solides mous tridimensionnels. La relaxation structurale s’effectue avec un temps de relaxation qui varie comme l’inverse du gradient de vitesse. Un comportement d'auto-guérison des fractures a été observé et lié à la relaxation structurale. Dans la deuxième partie, Chapitre 7, la croissance dendritique rapide d’alliages surfondus ternaires Ni-Co-Cu et quaternaires Ni-Co-Cu-Ge a été étudiée. La surfusion élevée est obtenue par lévitation électromagnétique et des méthodes de flux de verre. Les vitesses de croissance dendritiques ont été mesurées en fonction de la surfusion. Nous proposons une double fonction exponentielle pour décrire la relation entre la vitesse de croissance et la surfusion dans les alliages monophasiques. Un nouveau comportement a été observé : la vitesse de croissance des dendrites est abaissée en cas de séparation de phase et des mécanismes possibles sont proposés
This dissertation presents two topics related to the dynamics of interfaces: rheology of particle monolayers and the dendritic growth of alloys. In the first part, chapter1-6, the properties of silica nanoparticle monolayers at the air-water surface is presented and related to foam stability. The properties of the layers: textural evolution, surface pressure, thickness, particle contact angle with interface and effective surface concentration are characterized with respect to different particle hydrophobicities. The viscoelasticity of the layers are determined by three methods based on two Wilhelmy plates in the Langmuir trough. Remarkable differences between compressed layers and deposited layers have been found. The moduli present the maximum at intermediate particle hydrophobicity and depend on strain rate, initial particle quantity, trough length and age of the layer. The same universal linear and nonlinear behaviour as three-dimensional soft materials is found by a shear rheological study. The structural relaxation has been observed and the corresponding relaxation time has been characterized by SRFS method. A self-healing behavior is observed and a microscopic mechanism is proposed to account for the slow self-healing. The results suggests that the same physical process may involved in self heal as in structural relaxation. In the second part, chapter7, rapid dendritic growth in undercooled liquid ternary Ni-Co-Cu and quarternary Ni-Co-Cu-Ge alloys has been investigated. The high undercooling is obtained by electromagnetic levitation and glass flux methods. The dendritic growth velocities are measured as a function of undercooling. We propose a double exponential function to describe the relationship between growth velocity and undercooling in single phase alloys. A novel behavior that the dendritic growth velocity is reduced by liquid phase separation is found and the possible mechanism is proposed
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11

Farnoud, Amir Mohammad. "Interaction of polymeric particles with surfactant interfaces." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/4627.

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Films of phospholipids and biologically relevant surfactants at the air-water interface provide a well-defined medium to study molecular alignment, phase behavior and interactions of biomembranes and lung surfactant with exogenous materials. Interactions between lung surfactant interfaces and solid particles are of particular interest due to the increased use of nanomaterials in industrial applications and the promise of polymeric particles in pulmonary drug delivery. Understanding such interactions is necessary to avoid potential adverse effects on surfactant function after exposure to particles. In this thesis, the mechanisms of surfactant inhibition after exposure to submicron particles via different routes were investigated. The effects of carboxyl-modified polystyrene particles (200 nm) on films of dipalmitoyl phosphatidylcholine (DPPC) and Infasurf (calf lung surfactant extract) were studied. Surfactants were exposed to different concentrations of particles in a Langmuir trough with symmetric surface compression and expansion. Surface tension, potential, microstructure and topology were examined to monitor particle effects on surfactant function. Several methods of surfactant exposure to particles were studied: particle injection into the subphase after spreading surfactant monolayers (subphase injection), mixing the particles with the subphase and spreading the surfactant on top (monolayer addition) and particle aerosolization onto surfactant films. Studies with DPPC monolayers revealed that particle-surfactant interactions are dependent on the particle introduction method. In the subphase injection method, particles did not penetrate the monolayer and no inhibitory effects on surfactant function were observed. However, in the monolayer addition method, particles caused a premature monolayer collapse and hindered surfactant respreading likely by penetrating into the DPPC monolayer. Finally, particle aerosolization on surfactant was performed to mimic the physiologically relevant route of surfactant exposure to particles. Particle aerosolization on DPPC monolayers significantly inhibited surfactant function in the lung-relevant surface tension range. When aerosolized on Infasurf, particles caused inhibitory effects as a function of time suggesting adsorption of surfactant components on particle surfaces as the main mechanism of interaction. This research will enhance understanding of the mechanisms of particle-induced surfactant dysfunction, thereby providing information for the safe design of polymeric particles for drug delivery and for developing guidelines for particles used in occupational settings.
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12

Tinel, Liselotte. "Des réactions photochimiques aux interfaces atmosphériques." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10263/document.

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Les travaux présentés dans cette thèse portent premièrement sur la caractérisation de nouveaux photosensibilisateurs par des méthodes spectroscopiques. Ainsi les cinétiques de la réaction d'oxydation entre deux photosensibilisateurs à l'état triplet, imidazole-2-carboxaldehyde et 6-carboxypterine, et trois halogénures ont été déterminées par photolyse laser. La réactivité de l'état singulet de la 6- carboxypterine avec les halogénures et quatre acides organiques a été étudiée par fluorimétrie. Ces photosensibilisateurs sont relevants pour la photochimie à la surface de l'océan, mais également à la surface des particules atmosphériques. Les réactions mises en évidence mènent à la formation d'espèces radicalaires très réactives, influençant ainsi la composition de la phase condensée et gazeuse de l'environnement marin. La suite de cette étude s'est focalisée sur l'analyse des produits formés à partir de processus photo-induites à interface air-eau en présence d'une microcouche de surface d'un organique, utilisant deux organiques différents, l'octanol et l'acide nonanoique. En présence d'un photosensibilisateur et de lumière UVA, les changements en phase gaz ont été suivi par SRI-ToF-MS en ligne et en phase condensée par UPLC-(ESI)-HRMS. Ainsi on a démontré que la photochimie à la surface mène à la formation de produits fonctionnalisés et insaturés initiée par une abstraction d'hydrogène sur l'organique surfactant. Ces produits, observés en phase condensée et gazeuse, ont le potentiel de contribuer à la formation d'aérosols. Etonnamment, des produits ont également été observés dans les deux phases sans l'ajout d'un photosensibilisateur et montrant une activité photochimique de l'acide nonanoique seul à l'interface air-eau. Les mécanismes potentiels et les conséquences environnementales sont discutés
The works presented in this thesis concern firstly the characterization of two new photosensitizers by spectroscopic methods. This way the kinetics of the oxidation reaction between the triplet state of the photosensitizers, imidazole-2-carboxaldehyde and 6-carboxypterin, and three halides have been determined by laser flash photolysis. Also, the reactivity of the singlet state of 6-carboxypterin with halides and four organic acids has been studied by static fluorimetry. These photosensitizers are relevant for the photochemistry at the surface of the ocean, but also at the surface of atmospheric particles. The reactions evidenced by these studies lead to the formation of very reactive radical species influencing the composition of the condensed and gas phase of the marine environment. This study then focalized on the analysis of the products formed at the organic coated air-water interface through photo-induced processes. Two different organics were used as surfactants, octanol and nonanoic acid. In the presence of a photosensitizer and UVA light, the changes in the gas phase were monitored online by SRI-ToF-MS and in the condensed bulk phase by UPLC-(ESI)-HRMS offline analysis. These analysis showed that photochemical reactions at the interface lead to the formation of functionalized and unsaturated compounds initiated by a hydrogen abstraction on the organic surfactant. These products, observed in the condensed and gas phase have the potential to contribute to the formation of aerosols. Surprisingly, some of these products were also observed in the two phases without the presence of a photosensitizer, bringing into evidence a photochemistry of nonanoic acid at the air-water interface. Potential formation mechanisms of the products and environmental consequences are discussed
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13

Araújo, Juliana Botelho. "Measuring Air-Water Interfacial Areas: Contributions of Capillary and Film Domains in Natural Porous Media." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/333353.

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The air-water interface in variably saturated porous media is recognized to influence interfacial retention of organic and inorganic contaminants, and mediate various mass-transfer processes. The formation and presence of water films commonly solvating the surfaces of soil/sediment grains in unsaturated systems, as well as their impact on flow and retention processes have been of sustained interest. X-ray microtomography was used to measure air-water interfacial area at multiple wetting-phase saturations for natural porous media. First, a study was conducted to evaluate image-processing procedures suitable for characterizing fluids and associated interfaces in natural porous media. A simple method was developed for the analysis of all phases in the system, using global threshold for phase identification and combination of binary files (M1). This method was then compared to a simultaneous multiphase segmentation approach using locally adaptive threshold selection (M2). Both methods were used to process data sets comprised of multiple drainage steps for water-saturated packed columns imaged via synchrotron x-ray microtomography. The results of both methods were evaluated based on comparison of values determined for porosity and specific solid surface area to independently measured porosity and specific solid surface areas. The results show both methods are suitable for determination of total air-water interfacial area, which requires characterization of only the non-wetting phase. Conversely, determination of capillary interfacial area requires characterization of all phases present and thus, is more sensitive to the challenges associated with image processing. The simultaneous multiple-phase segmentation (M2) method provides an integrated and consistent analysis of the phases, and anticipated to improve water-phase detection. Using the advanced segmentation approach, the air-water interfacial area is presented as a result of direct measurement of contact areas between the two fluids. This is in contrast to previously reported data, which were derived indirectly from calculations based on individually measured phase surface areas and conceptualizations of fluid distributions. The effects of these assumptions on the capillary interfacial behavior are evaluated. Results from this study confirmed the initial hypothesis that the behavior of fluid surface areas will affect the theoretical shape of the capillary curve. The results support the understanding of the capillary interfacial area behavior in response to changes in the configuration of fluid surface areas during a drainage cycle. Furthermore, results for the measured air-water interface allows for further identification of fluid domains, such as the relationship between film interfacial area, capillary domains (menisci), and the total-measurable interfacial area. Experiments were also conducted using aqueous-phase interfacial partitioning tracer tests for comparison. Results support the hypothesis that different methods provide characterization of different interfacial domains. Overall, this study provides an imaging-based approach for evaluation of water configuration, and presents a measurement-based framework for further understanding of the role of fluid-fluid interfaces in natural porous media.
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14

Kim, Young Shin. "Investigating Langmuir films at the air-water interface using a planar array infrared reflection-absorption spectrograph." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 127 p, 2008. http://proquest.umi.com/pqdweb?did=1601522541&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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15

Ponzio, Florian. "Synthesis at different interfaces of bio-inspired films from mussels' byssus : influence of the oxidant nature at the solid/liquid interface and the addition of polymer at the air/water interface." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE041/document.

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Les matériaux à base de polydopamine (PDA) s’inspirent de la forte adhésion du byssus de la moule sous l’eau. L’oligomérisation de la dopamine dans un milieu basique permet la formation de revêtement de PDA sur n’importe quel matériau. En plus de la simplicité du procédé celui-ci est vert et versatile. La PDA a des propriétés similaires aux mélanines, d’où son utilisation dans le domaine des phénomènes de conversion d’énergie, de l’environnement et du biomédical. Cependant la structure de la PDA étant inconnue, l’élaboration de matériaux basés sur la relation structure propriétés est difficile. L’un des buts de cette thèse a été de comprendre cette relation pour élaborer de nouveaux matériaux de PDA. En choisissant l’oxydant adéquat nous avons déposé un film épais, superhydrophile et biocompatible sur n’importe quels substrats. De plus nous avons découverts la possibilité de former des films de PDA à l’interface air/eau. L’étude de ce phénomène a permis de former des membranes autosupportées et stimuli responsives
Polydopamine (PDA) materials are inspired from mussels’ byssus strong adhesion underwater. The oligomerization of dopamine in a basic medium allows forming a PDA coating on virtually any materials. In addition to the simplicity, ecofriendly and versatility of the deposition method, PDA has properties similar to those of melanin pigments and displays many outstanding properties. Thus PDAis widely used in energy, environmental and biomedical sciences. However design of PDA based new materials with tailored properties is a challenge since its structure is still unknown. In that sense one of the aims of this thesis is to gain knowledge in PDA structure-property relationship in order to design PDA materials with new properties. By choosing the appropriate oxidant we deposited thick and superhydrophylic films on any materials for the elaboration of low fouling and biocompatible surfaces. Additionally we discovered the possibility to form PDA films at the air/water interface. The investigation of this phenomenon led to the formation of stimuli responsive free standing membranes
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16

Andersen, Audrée. "Surfactant dynamics at interfaces : a series of second harmonic generation experiments." Phd thesis, Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2006/655/.

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Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus.

There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model.

The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model.

Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants.
Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen.

Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert.

Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden.
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17

Matmour, Rachid. "Application of lithium/halide exchange reactions to the synthesis of complex polymer architectures : investigation of their self-assembling properties at the air/water." Bordeaux 1, 2006. http://www.theses.fr/2006BOR13368.

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Une nouvelle famille d'amorceurs et de macroamorceurs pluricarbanioniques solubles en solvant apolaire a été synthétisée par une réaction d'échange halogène-lithium (réaction de Gilman) effectuée sur des composés halogénés (macro)moléculaire. L'utilisation de ces espèces pluricarbanioniques comme (macro)amorceurs a permis la synthèse de différentes architectures polymères complexes -copolymères triblocs, polymères en étoile, polymères à architecture dentrique- par polymérisation anionique par voie divergente. L'intérêt potentiel d'architectures polymères tels que les copolymères amphiphiles en étoile poly-butadiène-b-oxyde d'éthylène) à l'interface air/eau a pu être démontré à travers la synthèse de nanomatériaux polymères bidimensionnels basés sur un réseau en deux dimensions de polybutadiène réticulé possédant des domaines de poly(oxydes d'éthylène) de tailles contrôlées piégés au sein du réseau. Pour atteindre cet objectif de nouveaux copolymères en étoile (PB(Si(OEt)3-b-PEO)3 ont été synthétisés par hydrosilylation des doubles liaisons pendantes du précurseur en étoile (PB-b-PEO)3 en présence de triéthoxysilaine. La condensation des groupements triéthoxysilane en condition acide à permis la réticulation des blocs polybutadiène directement à l'interface air/eau en l'absence de tout additif ou réactif.
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18

Pezzotti, Simone. "DFT-MD simulations and theoretical SFG spectroscopy to characterize H-Bonded networks at aqueous interfaces : from hydrophobic to hydrophilic environments Structural definition of the BIL and DL: a new universal methodology to rationalize non-linear χ(2)(ω) SFG signals at charged interfaces, including χ(3)(ω) contributions What the Diffuse Layer (DL) Reveals in Non-Linear SFG Spectroscopy 2D H-Bond Network as the Topmost Skin to the Air-Water Interface Combining ab-initio and classical molecular dynamics simulations to unravel the structure of the 2D-HB-network at the air-water interface 2D-HB-Network at the air-water interface: A structural and dynamical characterization by means of ab initio and classical molecular dynamics simulations Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface Molecular hydrophobicity at a macroscopically hydrophilic surface Graph theory for automatic structural recognition in molecular dynamics simulations DFT-MD of the (110)-Co3O4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLE008.

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Améliorer notre connaissance de la structure de l'eau dans l'environnement spécial offert par une interface est essentiel pour la compréhension de nombreux phénomènes naturels et applications technologiques. Pour révéler cette structure interfaciale de l'eau, des techniques capables de fournir des informations microscopiques, de manière sélective, pour cette couche interfaciale (BIL) sont nécessaires. Dans le présent travail de thèse, nous avons donc étudié les interfaces aqueuses au niveau moléculaire, en couplant la modélisation théorique à partir de simulations DFT-MD avec les spectroscopies SFG et THz-IR. En développant de nouveaux protocoles/outils d'investigation associant simulations DFT-MD et spectroscopie SFG, en particulier pour la rationalisation plus complexe des interfaces chargées, nous avons fourni une compréhension globale de l'effet des conditions interfaciales d'hydrophilicité, de pH, de force ionique sur le réseau des liaisons-H formé dans la couche interfaciale BIL, sur ses signatures spectroscopiques et sur son impact sur les propriétés physico-chimiques. Nous avons montré pour la première fois que, dans des conditions suffisamment hydrophobes, l'eau interfaciale crée des réseaux des liaisons-H bidimensionnels, révélé expérimentalement par les spectres THz-IR. Le réseau-2D dicte la dynamique de l'eau interfaciale, le potentiel de surface, l'acidité de surface, la tension superficielle et la thermodynamique d'hydratation des solutés hydrophobes. Cet "ordre horizontal" aux interfaces hydrophobes est opposé à "l'ordre verticale" obtenu aux interfaces hydrophiles. Nous avons aussi révélé comment les ions et les conditions de pH modifient ces arrangements structuraux
Improving our knowledge on water H-Bonded networks formed in the special environment offered by an interface is pivotal for our understanding of many natural phenomena and technological applications. To reveal the interfacial water arrangement, techniques able to provide detailed microscopic information selectively for the interfacial layer are required. In the present thesis work, we have hence investigated aqueous interfaces at the molecular level, by coupling theoretical modeling from DFT-MD simulations with SFG & THz-IR spectroscopies. By developing new investigation protocols/tools, coupling DFT-MD simulations and SFG spectroscopy, in particular for the more complex rationalization of charged interfaces, we have provided a global comprehension of the effect of various interfacial conditions (hydrophilicity, pH, ionic strength) on the HB-Network formed in the interfacial layer (BIL), on its spectroscopic signatures and on its impact on physico-chemical properties. We have shown for the first time that, in sufficiently hydrophobic conditions, BIL interfacial water creates special 2-Dimensional HB-Networks, experimentally revealed by one specific THz-IR marker band. Such 2D-network dictates HBs and orientational dynamics of interfacial water, surface potential, surface acidity, water surface tension and thermodynamics of hydration of hydrophobic solutes. Such "horizontal ordering” of water at hydrophobic interfaces is found opposite to the “vertical ordering” of water at hydrophilic interfaces, while coexistence of the two orders leads to disordered interfacial water in intermediate hydrophilic/hydrophobic conditions. Both DFT-MD and SFG further revealed how ions & pH conditions alter these BIL-water orders
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19

Carter-Fenk, Kimberly Anne. "Structure, Adsorption Mechanisms, and Vibrational Exciton Formation at Proxy Marine Interfaces." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1617809603306859.

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20

Bai, Hongjuan. "Bio-colloidal transfer in saturated and unsaturated porous media : influence of the physical heterogeneity of the porous medium and cell properties on bacteria transport and deposition mechanisms." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2336/document.

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La compréhension du transport et du dépôt bio-colloïdal dans un milieu poreux présente un grand intérêt dans les applications environnementales, en particulier pour le contrôle de la bio-remédiation des sols et la protection des ressources en eau souterraine. Afin de mieux évaluer et prévenir les risques de contamination de la nappe phréatique et de proposer des solutions adéquates de remédiation, il est nécessaire d’avoir une bonne compréhension des mécanismes qui contrôlent le transport et le dépôt des bactéries dans les milieux poreux saturés et non saturés. L’objectif des ces travaux de thèse est d’étudier le rôle de l’hétérogénéité physique du milieu poreux (distribution granulométrique, porosité…) et de l’hydrodynamique du milieu sur les mécanismes de transport et de dépôt de particules bio-colloïdales, tout en prenant en compte l’impact des propriétés de cellules bactériennes sur ces mécanismes. Des expériences de traçage et d’injection de suspensions bactériennes ont été menées à l’échelle de colonnes de laboratoire dans trois milieux poreux avec une porosité et une distribution de taille de pore distincte. Afin de caractériser l’écoulement dans les milieux poreux, un soluté non-réactif a été utilisé comme traceur de l’eau. Trois souches bactériennes ont été utilisées pour préparer les suspensions bactériennes : une bactérie mobile (Escherichia coli), et deux non mobiles (Klebsiella sp. et R. rhodochrous). La caractérisation des propriétés cellulaires (telles que la taille et la forme des cellules, le potentiel zêta, la motilité et l'hydrophobicité) a été effectuée pour chaque souche. Des simulations numériques ont été réalisées en utilisant le code de calcul HYDRUS-1D afin de modéliser l’écoulement et d’estimer les paramètres de transport et de dépôt des bactéries. Ces derniers ont été explorés afin d'identifier le mode de transport bactérien et les mécanismes physico-chimiques ou physiques impliqués dans le dépôt des bactéries. Des expériences supplémentaires à l'échelle des pores ont été réalisées à l'aide de dispositifs microfluidiques conçus à cet effet. Un calcul théorique des différentes interactions entre les bactéries et le milieu poreux aux interfaces air/eau/solide a été effectué pour compléter les résultats expérimentaux ainsi que ceux issus de la modélisation numérique. Ainsi, les énergies d’interactions telles que les forces de van der Waals, électrostatiques de double couche, hydrophobes, stériques, capillaires et hydrodynamiques, impliquées dans le dépôt de bactéries ont été calculées pour décrire les interactions bactéries-interfaces afin d'identifier leur impact relatif sur le dépôt physico-chimique et physique des bactéries. Les résultats expérimentaux et la modélisation numérique ont mis en évidence un écoulement non uniforme, dépendant de la taille des grains ainsi que de la distribution de la taille des pores du milieu poreux. Pour un milieu poreux donné, l’écoulement devient plus dispersif quand la teneur en eau du milieu diminue. Ceci est dû à l’augmentation de la tortuosité du milieu, du fait de la présence de l’air dans les pores. Le transport des bactéries diffère de celui du traceur de l’eau. Le dépôt bactérien a été fortement influencé par la géométrie du réseau poral du milieu, les propriétés cellulaires et le degré de saturation en eau. Le piégeage physique et physico-chimique sont des mécanismes qui doivent être pris en compte pour bien décrire le dépôt bactérien, mais leur importance sur les mécanismes de dépôt est étroitement liée aux propriétés du milieu poreux et des cellules. Ces travaux mettent en évidence l’effet simultané des propriétés cellulaires, des propriétés physiques (granulométrie et distribution de taille de pores) et de l'hydrodynamique du milieu poreux sur les mécanismes de transport et de dépôt bactérien. Le calcul des différentes énergies d’interaction a permis d’identifier leur importance sur les mécanismes de dépôt bactérien
The investigation of the transport and retention of bacteria in porous media has a great practical importance in environmental applications, such as protection of the surface and groundwater supplies from contamination, risk assessment from microorganisms in groundwater, and soil bioremediation. The aim of this study is to gain a fundamental understanding of the mechanisms that control bacteria transport and deposition in saturated and unsaturated porous media. Laboratory tracer and bacteria transport experiments at Darcy scale were performed in three porous media with distinct pore size distribution in order to investigate and quantify water and bacteria transport process under steady state flow conditions. A conservative solute was used as water tracer to characterize water flow pathways through porous media. A gram negative, motile Escherichia coli, a gram negative, non-motile Klebsiella sp. and a gram positive, non-motile R. rhodochrous were selected for the transport experiments. Characterization of cell properties (such as cell size and shape, zeta potential, motility and hydrophobicity) was performed for each strain. Numerical simulations with HYDRUS-1D code were performed to characterize water flow and to estimate bacteria transport and deposition parameters. The later were explored to identify bacteria flow patterns and physicochemical or physical mechanisms involved in bacteria deposition. To provide a better understanding of the mechanisms involved on bacteria transport and deposition, pore scale experiments were carried out by using microfluidic devices, designed for this purpose. The information obtained from laboratory experiments and numerical modeling was improved by theoretical calculation of different interactions between bacteria and porous media at air/water/solid interfaces. DLVO and non-DLVO interactions such as hydrophobic, steric, capillary and hydrodynamic forces involved in bacteria deposition were considered to describe bacteria-interface interactions in order to identify their relative impact on physicochemical and physical deposition of bacteria. Results obtained through both laboratory experiments and numerical simulationsoutlined non-uniform flow pathways, which were dependent on both grain/pore size as well as pore size distribution of the porous media. For a given porous medium, water flow patterns became more non-uniform and dispersive with decreasing water saturation due to the presence of air phase, which lead to an increase of the tortuosity of the flow pathways under unsaturated conditions. Bacteria transport pathways were different from the tracer transport, due to size exclusion of bacteria from smaller pore spaces and bacteria motility. Bacteria deposition was greatly influenced by pore network geometry, cell properties and water saturation degree. Both physical straining and physicochemical attachment should be taken into account to well describe bacteria deposition, but their importance on bacteria deposition is closely linked to porous media and cell properties. The results obtained in this work highlighted the simultaneous role of cell properties, pore size distribution and hydrodynamics of the porous media on bacteria transport and deposition mechanisms. The calculation of DLVO and non-DLVO interactions showed that bacteria deposition in saturated and unsaturated porous media was influenced by both kinds of interactions
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21

Zhang, Ju. "Poly(N-isopropylacrylamide) at the air/water interface." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0024/NQ51026.pdf.

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22

Zhang, Ju. "Poly(N-isopropylacrylamide) at the air/water interface /." *McMaster only, 1998.

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23

Chang, Brian Lida. "Crossing the Air-Water Interface: Inspiration from Nature." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/83445.

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This dissertation aims to contribute toward the understanding of water-entry and -exit behaviors in nature. Since water is nearly a thousand times denser than air, transitioning between the two mediums is often associated with significant changes in force. Three topics with implications in water-entry are discussed, along with a fourth topic on water-exit. For a plunge-diving seabird, the first two stages of water-entry (initial impact and air-cavity formation) create large stresses on the bird's neck. Linear stability analysis of a cone-beam system impacting water shows buckling and non-buckling behaviors on the beam, which is extended to the diving birds. The next topic is related to the third stage of water-entry (air-cavity pinch-off), in which the chest feathers come in contact with the water. Here, the elasticity of Northern Gannet contour feathers is calculated using the nonlinear bending equation. The third topic will explore the formation of ripples along air cavity walls and their resulting force after pinch-off. An acoustic model predicts the observed wavelengths of the ripples. The final topic will delve into the mechanics of how animals leap out of water. A scaling law that balances the power of thrust and drag will predict the height of the jump. Finally, a bio-inspired robot was built to help identify physical conditions required to jump out of water.
Ph. D.
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24

Williams, David F. "Aggregation of colloidal particles at the air-water interface /." Thesis, Connect to this title online; UW restricted, 1991. http://hdl.handle.net/1773/9912.

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25

De, Samaniego Maria Simon Saenz. "Photopolymerisation of surfactant monolayers at the air-water interface." Thesis, University of Manchester, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506596.

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26

Creazzo, Fabrizio. "Oxygen evolution reaction at cobalt oxides/water interfaces : heterogeneous electrocatalysis by DFT-MD simulations & metadynamics Ab initio molecular dynamics study of an aqueous NaCl solution under an electric field Ionic diffusion and proton transfer in aqueous solutions of alkali metal salts Ionic Diffusion and Proton Transfer in Aqueous Solutions under an Electric Field: State-of-The-Art Ionic diffusion and proton transfer of MgCl2 and CaCl2 aqueous solutions: an ab initio study under electric field DFT-MD of the (110)-Co 3 O 4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment Enhanced conductivity of water at the electrified air–water interface: a DFT-MD characterization Ions tune interfacial water structure and modulate hydrophobic interactions at silica surfaces." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASE012.

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Dans cette thèse, des simulations DFT-MD couplées à des techniques inno-vantes de métadynamique, sont appliquées pour acquérir une compréhensionglobale des interfaces aqueuses d'oxyde de cobalt Co3O4 et CoO(OH) dansla catalyse de la réaction d'évolution de l'oxygène (OER), et ainsi éventuellement aider à la conception de nouveaux catalyseurs basés sur des matériaux non précieux, un domaine clé de la recherche scientifique et technologique, particulièrement important pour l'économie de l'hydrogène, pour les technologies vertes dans une période de temps avec une demande toujours plus croissanteen énergie verte. Dans cette thèse, nous révélons étape par étape les mécanismes de l'OER sur les électrocatalyseurs aqueux d'oxyde de cobalt Co3O4 etCoO(OH) via de nouvelles techniques de métadynamique.Jusqu'à présent, la littérature n'a jamais pris en compte les modificationsau niveau atomique de la structure des électrodes ainsi que de l'eau interfaciale dans leur modélisation des processus OER. Ce manque de connaissances représente clairement un obstacle important au développement de catalyseurs améliorés, qui pourrait être surmonté en utilisant des méthodes capables de suivre les caractéristiques catalytiques de l'OER à l'échelle atomique. Pour la première fois, nous montrons combien il est important de prendre en considération la présence de l'environnement aqueux dans la caractérisation structurale des surfaces du catalyseur, c'est-à-dire (110)-Co3O4 et (0001)-CoO(OH) dans ce travail. Une caractérisation détaillée des propriétés chimiques et physiques des interfaces aqueuses est fournie (la structure, la dynamique, la spectroscopie, le champ électrique), pour les surfaces (110)-Co3O4 et (0001)-CoO(OH) en contact avec l'eau liquide.Une étude détaillée de l'OER est présentée non seulement du point de vue descatalyseurs, mais aussi en abordant le rôle de l'environnement de l'eau dans leprocessus catalytique, ce qui n'a pas été fait auparavant dans la littérature. En conséquence, l'OER en phase gazeuse et en phase liquide sont étudiés ici auxinterfaces aqueuses (110)-Co3O4 et (0001)-CoO(OH) en adoptant une nouvelleapproche de métadynamique d'échantillonnage amélioré, capable d'identifieret caractériser les mécanismes de réaction chimique et d'intégrer pleinement lerôle des degrés de liberté du solvant, permettant ainsi de dévoiler des réactivités chimiques d'une complexité remarquable. L'énergétique, la cinétique et la thermodynamique derrière l'OER sont donc trouvées à ces surfaces d'oxyde de cobalt à l'interface avec l'eau
In this thesis, DFT-MD simulations, coupled with state-of-the-art metadynamics techniques, are applied to gain a global understanding of Co3O4 and CoO(OH) cobalt oxide aqueous interfaces in catalyzing the oxygen evolution reaction (OER), and hence possibly help in the design of novel catalysts basedon non-precious materials, a current key field of research in science and technology, especially of importance for the hydrogen economy, for green technology in a period of time with an ever more growing demand in green-energy. In this thesis, we step-by-step reveal the OER mechanisms on spinel Co3O4 andCoO(OH) cobalt aqueous electrocatalysts carefully and rationally via novelmetadynamics techniques.Up to now, the literature has never taken into account the atomistic modifications on the electrode structure as well as on the interfacial water into their modeling of OER processes. Such lack of knowledge clearly represents a significant hurdle toward the development of improved catalysts, which couldbe overcome by employing methods able to track the catalytic features of theOER at the atomistic scale. For the first time, we show how important itis to take into consideration the presence of the liquid water environment inthe structural characterization of catalyst surfaces, i.e. for (110)-Co3O4 and(0001)-CoO(OH) in this work. A detailed characterization of chemical andphysical properties of the aqueous interfaces is provided (i.e. structure, dynamics, spectroscopy, electric field), for the (110)-Co3O4 and (0001)-CoO(OH)aqueous surfaces.A study of the OER is presented not only by looking at the catalysts, butalso by addressing the role of the water environment in the catalytic process,not done before in literature. Accordingly, both gas-phase and liquid-phaseOER are here investigated at the (110)-Co3O4 and (0001)-CoO(OH) adoptinga novel enhanced sampling metadynamics approach able to address a widerange of chemical reaction mechanisms and to fully include the role of thesolvent degrees of freedom, allowing to unveil reaction networks of remarkablecomplexity. The energetics, kinetics and thermodynamics behind the OER aretherefore found at these cobalt oxide surfaces
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27

Meszaros, Caroline Michele. "Morphologies of block polyelectrolyte aggregates at the air-water interface." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69642.

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The surface properties of novel 2-D nanoemulsions, composed of mixtures of the perquaternized diblock poly(styrene$ sb{260}$-block-4-vinylpyridinium$ sb{240}$) and homopolystyrene spread at the air-water interface, were thoroughly studied using the Langmuir film balance and microscopy techniques (transmission electron microscopy and atomic force microscopy). The effects of both the molecular weight of homopolystyrene and the amount added were explored. It was found that the surface morphology could be manipulated in a predictable way by the addition of homopolystyrene. The surface films of the diblock families poly(styrene-block-sodium acrylate) and poly(styrene-block-sodium methacrylate) spread at the air-water interface were also investigated. The morphologies of their surface aggregates, i.e., jellyfish micelle, ribbon, and plane, were studied as parameters such as temperature and sub-phase electrolyte concentration were varied. A novel morphology, the 2-D nanofoam, was also investigated. The cellular walls of the 2-D nanofoams are found to consist of the polystyrene blocks of thickness on the order of the radius of gyration of the polystyrene blocks. Quantitative analysis of these cellular networks provides results similar to macroscopic 2-D surfactant foams indicating that the same forces are operative in both systems.
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28

Jackson, Andrew. "Neutron scattering from surfactants adsorbed at the air/water interface." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289322.

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29

Zhang, Xiao Li. "Adsorption of polyelectrolyte/surfactant mictures at the air-water interface." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531793.

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30

Mizak, Constance Anne. "Ammonia flux at the air/water interface of Tampa Bay." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000273.

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31

Goodman, Matthew Dave. "Cadmium-based nanocrystals and nanocomposites at the air-water interface." [Ames, Iowa : Iowa State University], 2009.

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32

Gessner, Jana Verena. "Computational modelling of fatty acids at the air-water interface." Thesis, University of Reading, 2018. http://centaur.reading.ac.uk/78955/.

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The organic fraction of aqueous atmospheric aerosols has received much recent attention due to the ability of fatty acids to partition to the air-water interface, thus altering the surface properties of the aerosol. With the complex surface films formed, there is a need for an efficient model system to understand key features. To further both our understanding of film formation processes and changes in films due to ozonolysis reactions within the atmosphere, this work employs coarse-grained molecular dynamics simulations of model surfactants at the air-water interface. Molecular dynamics simulations of surface films have not yet been widely used in atmospheric science; however, they can provide useful insight into sub-micrometre aerosols, giving a molecular level view of the structure and dynamics of the system. Thus, this work paves the way for future coarse-grained simulations in the field of atmospheric chemistry. In the simulations in this thesis, a planar interface is assumed, mimicking a cross-section through a large aerosol with low curvature and allowing direct comparison to experimental studies on Langmuir troughs. Based on structural data derived from allatom simulations, pressure-area isotherms were calculated from coarse-grained simulations of single component monolayers of oleic acid, stearic acid and palmitoleic acid, which were in good agreement with experimental isotherms. The phase behaviour of the main reaction products of the ozonolysis of both oleic acid and palmitoleic acid, assuming an analogue reaction pathway as for oleic acid, were determined. The simulations suggest that the only products remaining at the interface from these reactions are nonanoic acid and heptanoic acid. Pressure-area isotherms of mixed component films, which are more realistic proxies for the complex mixtures on real atmospheric aerosols, were then calculated. For systems below 10 % unsaturated material, ordered liquid-condensed phase and solid state films were formed. These may act as a transport barrier and hence supress the growth of aerosols in the atmosphere. For surface films containing more than 33 % of unsaturated material, disordered liquidexpanded films were formed. For such films, the higher the amount of unsaturated material, the higher the surface pressure of the system, and the lower the surface tension. It was shown that the ozonolysis of a surface film can lead to phase changes, hence influencing the growth potential of the aerosol, and highlighting the importance of a complete understanding of aged surface films in the atmosphere.
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33

Hendrickson, Kelli L. "Navier-Stokes simulations of steep breaking water waves with a coupled air-water interface." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33559.

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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2005.
Includes bibliographical references (p. 367-378).
Wave breaking on the ocean surface significantly facilitates the transfer of mass, momentum, heat and energy across the air-sea interface. In the context of the near field flow about a surface ship, the breaking bow wave is a key element to the bubbly signature and an appreciable portion of the wave drag of the ship. Yet, despite its direct effect on many aspects of ocean engineering, this phenomenon is not well understood even at a basic level. Most of the knowledge has been contributed by experiments in the laboratory and the field although results are often limited due to the difficulty in taking measurements of local quantities during the breaking event. Numerical solution of the breaking wave problem has generally been limited to the pre-breaking phase as it avoids complex mechanisms such as surface re-entry, spray formation, air entrainment and strong turbulence. Additionally, relatively few experimental or numerical studies exist which dynamically couple the air-water interface. The objective of this thesis is to contribute to the knowledge of steep breaking waves in the context of the coupled air-water interface. Of central importance are basic kinematics and dynamics, the rate of energy dissipation and energy flux at the interface during the breaking event.
(cont.) To this end, a systematic study of a range of breaking waves is performed by direct numerical simulation (DNS) of the Navier- Stokes equations using an Eulerian interface capturing method. The advantage of the DNS approach is that all physical scales are resolved and no turbulence closure models are necessary. However, because of this, DNS is limited to the study to moderate Reynolds numbers with a relatively high computational cost for each simulation. For this reason, this study is limited to two-dimensional flows at Reynolds number 0(10³). The interface capturing method used is a modified form of the level set method which is better suited for simulating coupled air-water flows. The level set method provides a natural numerical treatment of the coupled air-water interface through complex surface topology changes. Thus, no ad-hoc treatment of the air-water interface during the breaking event is necessary. The key findings of this thesis represent new contributions to the study of breaking waves in three distinct areas. The first is the kinematics and dynamics of deep water breaking waves for both spilling and plunging types. For the waves in this study, there was no indication of flow reversal or separation in the water while the air flow showed separation on the front face of the wave and over the crest.
(cont. ) Localized shear regions are found in spilling breaking waves and curvature effects are identified as the dominant mechanism of vorticity generation in both types of breaking waves. The second area is the energy dissipated by breaking waves. The volumetric dissipation rates as well as its spatial variation for both air and water are presented for the range of waves in this study. While the water volume experienced an increase in dissipation rate during the breaking event, the increase is more pronounced in the air volume to the point that it becomes the same order of magnitude as that in the water for some waves. The amount of energy in the wave lost due to breaking is quantified as a function of the energy in the wave prior to breaking. A threshold below which waves do not break is identified and qualitative comparisons to experiment are made when applicable. The third area is the transfer of energy at the air-water interface during breaking which is an aspect of the breaking process that has not received much attention in the literature. In this thesis, the formulation of a term in the energy equation which accounts for the energy flux rate at the air-water interface is presented. The waves in this numerical study give evidence that this quantity is appreciable.
(cont.) Although the calculation of this term is sensitive to errors associated with the conservation of energy, values as high as 25% of the energy lost to breaking are found. At the Reynolds numbers in this study, the dominant mechanism for each type of wave is identified as inviscid for spilling breaking waves and viscous for plunging breaking waves. This numerical effort has contributed to the basic knowledge of wave breaking at moderate Reynolds numbers. Through the inclusion of the coupled air-water interface, unique insight to the kinematics, dynamics, dissipation and energy fluxes of breaking waves was obtained. The information gained in this study provides an initial step towards physics-based turbulence models for the study of wave breaking at larger scales.
by Kelli L. Hendrickson.
Sc.D.
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34

Wang, Xiaolu. "Janus Colloids Surfing at the Surface of Water." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS272/document.

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Considérant une particule isolée, la différence principale entre un colloïde actif et un colloïde passif réside dans le temps de persistance du régime balistique. La transition du régime balistique vers le régime diffusif est déterminée dans les deux cas par des coefficients de friction ou de manière équivalente par des coefficients de diffusion. Le mouvement d’une particule colloïdale passive micrométrique est diffusif lorsqu’il est observé sur des intervalles de temps d’au moins une microseconde, suffisamment longs pour que la direction de la quantité de mouvement soit rendue aléatoire par des collisions avec les molécules de solvant. A l’échelle macroscopique ces collisions se traduisent par un coefficient de friction de translation. Pour une particule colloïdale active, un mouvement diffusif est observé pour des intervalles de temps de plusieurs secondes, suffisamment longs pour que la direction d’auto-propulsion soit rendue aléatoire par la diffusion rotationnelle de la particule.Dans cette thèse, nous étudions le mouvement d’une particule colloïdale active déposée à la surface de l’eau. Des particules Janus aux propriétés catalytiques ont été préparées par dépôt de platine métal à la surface de particules de silice. La profondeur d’immersion des particules ainsi que leur orientation par rapport à la surface de l’eau ont été caractérisées et discutées en tenant compte des propriétés de mouillage non-uniformes de la surface des particules Janus. Le mouvement de particules isolées en présence de quantités variables d’eau oxygénée utilisée comme source d’énergie, a été enregistré par vidéo-microscopie optique et les trajectoires analysées en termes de déplacement carré moyen et de fonction d’auto-corrélation des vitesses. L’observation de deux types de trajectoires, rectilignes et circulaires, révèle la force effective ainsi que le couple induit par la décomposition catalytique de l’eau oxygénée à la surface de la particule Janus. Le résultat principal de ce travail est que le mouvement des particules actives confinées à l’interface persiste plus longtemps dans le régime balistique que celui de particules actives totalement immergées en solution. Ceci est dû au confinement qui réduit le nombre de degrés de liberté de rotation mais aussi aux conditions de mouillage partiel qui font apparaître des contributions supplémentaires à la friction de rotation
At the single-particle level, the main difference between active colloids and passive ones is the time scale over which the motion crosses over from ballistic to diffusive regime. In both cases, friction coefficients or equivalently diffusion coefficients determine this time scale. For instance, the motion of a passive colloid of 1m radius is diffusive when observed over lag times longer than a microsecond, once the direction of its momentum has been randomized by collisions with solvent molecules. At the macroscopic scale these collisions are accounted for by the translational friction coefficient. For an active colloid the effective diffusive behavior observed over lag times larger than few seconds results from the randomization of the direction of self-propulsion by rotational diffusion. In this thesis we investigated the motion of an active Janus colloid trapped at air-water interface. Spherical catalytic Janus colloids have been prepared through the deposition of platinum metal at the surface of silica particles. Immersion depth of the Janus colloid as well as their orientation with respect to the water surface, has been characterized and interpreted in terms of the non-uniform wetting properties of the Janus particles. The motion of the active Janus colloids in the presence of various concentration of hydrogen peroxide H2O2 as fuel was characterized by video microscopy and the trajectories analyzed through the mean square displacement and the velocity autocorrelation function. The types of trajectories, directional and circular ones that we observed in our experiments, revealed the effective force and torque induced by the catalytic decomposition of H2O2. At the water surface, active colloids perform more persistent directional motions as compared to the motions performed in the bulk. This has been interpreted as due to the loss of degrees of freedom resulting from the confinement at interface and also to the partial wetting conditions that possibly bring new contributions to the rotational friction at interface
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35

Ann, De Bry Beth. "Optical spectroscopy of organic thin films at the air-water interface." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/30405.

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36

Rippner, Blomqvist Brita. "Non-ionic block copolymers and proteins at the air-water interface." Doctoral thesis, Stockholm : Surface Chemistry, Department of Chemistry, Royal Institute of Technology, Ytkemiska institutet, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-165.

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37

Gokhale, Prasad N. "Mixed convective heat transfer and evaporation at the air-water interface." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1202500424/.

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38

Peace, Stella Kirsten. "Organisation and dynamics of amphiphilic systems at the air-water interface." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5389/.

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The behaviour of polymeric amphiphiles, specifically systems containing poly( methyl methacrylate), PMMA, and poly(ethylene oxide), PEO, spread at the air water interface is reported. An amphiphilic graft copolymer containing a PMMA backbone and PEO side chains forms the main subject of the study. Films of PMMA spread onto a 0.1 wt.% solution of PEO have also been considered. Due to the presence of a surface excess, both PEO and PMMA populate the surface and the latter system provides a model of the graft copolymer. Monolayer behaviour has been characterised by recording surface pressure isotherms. It has been demonstrated that the behaviour of the graft copolymers is highly composition dependent, exhibiting characteristics associated with the constituent homopolymers. In contrast the surface pressure isotherm for PMMA on PEO solution is quite unlike that for PMMA on water. Details of the structural organisation in these systems have been determined using neutron reflectometry. The surface organisation adopted by the graft copolymers varies as the surface concentration increases. The PEO side chains penetrate the subphase and stretch increasingly whereas the PMMA backbone behaves much like the homopolymer. This is in contrast to the behaviour of PMMA on PEO solution where the PMMA occupies a wider region of the interface. The structure of the adsorbed PEO differs from that of the bare solution but maintains a constant surface excess. Dynamic behaviour has been studied using surface quasi elastic light scattering. For the graft copolymers surface wave evolution is very unusual. The dilational parameters provide evidence, e.g. a negative dilational viscosity, indicating that surface wave propagation is complex and not described fully by current theories. Similar behaviour is exhibited by PMMA on a PEO solution. These features are believed to be associated with subphase penetration and are discussed in this context.
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39

Timson, Andrew John. "Second harmonic generation of molecules located at the air/water interface." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326716.

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40

Mölder, Erik. "Measurement of the oxygen mass transfer through the air-water interface /." Tartu: Tartu University Press, 2005. http://dspace.utlib.ee/dspace/bitstream/10062/616/5/molder.pdf.

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41

Li, Tao. "Self-assembly of rod-like colloids at the air-water interface." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20993.

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Two-dimensional (2D) colloidal materials and their assembly are of scientific significance and industrial importance. The development of 2D colloidal structures is a key stepping stone towards three-dimensional (3D) structures in relation to controlled chemical composition, morphology, assembly and so on. Nowadays, uniform colloidal structures with complexity in both shape and interactions have become a popular topic in fundamental colloid science and applications. Being motivated by this, in this thesis, micro-scale colloidal rods and self-assembled dipeptides have been studied experimentally at the air-water interface. Monolayers containing these colloidal materials were created in a Langmuir trough. Surface pressure measurements, microscopic observations and many other techniques were combined for the investigation. The aim of this work is to understand the phase behaviours in complex monolayers, including the phase transitions during compression, the flipping dynamics of micro-rods, the contribution of dipole-dipole interactions between magnetic rods, and the interfacial self-assembly process of dipeptide molecules. Iron oxide micro-rods (β-FeOOH @silica) with different aspect ratios have been synthesized to create the monolayers at an air-water interface. Microscopic observations reveal a sequence of phase transitions by compressing the monolayers. It has been proved that the aspect ratio of the rods plays an important role in the phase transitions, —short rods flip into a perpendicular position relative to the interface to relieve the compressional stress, while longer rods form multilayers under compression. Magnetic rods (Fe3O4) were converted from the synthesized FeOOH rods. They can be aligned in an external field, which further induces the reorganization at the interface. To study these magnetic rods, differential dynamic microscopy (DDM) was carried out to measure the magnetic moment. Their interfacial properties were investigated in an external field applied perpendicular and parallel to the interface, respectively. A magnetic field-induced flipping process has been observed, which proves the theoretical prediction. Besides rod-like particles, naphthalene dipeptides have been successfully trapped at the interface of a low pH subphase, self-assembling into a hydrogel film. The mechanism of interfacial self-assembly has been studied. Both FTIR spectra and AFM images are used to investigate the fibrous structures of the film. The film has elastic properties and buckles under compression. Moreover, dipeptide hydrogel induced by metal ions has been used to create a wet foam system, which owns the advantages of long-term stability (more than two weeks), low cost, and easy preparation.
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42

Omur-Ozbek, Pinar. "Macromolecular Reactions and Sensory Perception at the Air-Water-Human Interface." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/77226.

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During 20th century main concern was to have sanitary water flowing through the tap. In 21st century constant supply of safe drinking water is common at any home in USA. Hence consumers pay attention to aesthetic quality of tap water. Odorous algal metabolites in source water and metals introduced to drinking water due to corrosion of pipes in the distribution system cause taste, odor and color problems, and result in complaints and perception of tap water as unhealthy. Millions of dollars are spent each year by water industry to address and prevent these issues. This research focused on some of the taste-and-odor issues associated with drinking water. First aim was to understand when geosmin, 2-MIB, and nonadienal become detectable, employing two-resistance mass transfer theory to determine the concentration of odorants in bathroom air. Results showed that water temperature and odorant concentration in water play an important role. Next focus was to develop an international odor standard to be used for training of sensory analysis panelists. There are many sensory methods to monitor drinking water to detect the off-flavors however an odor standard has been missing. Hexanal was studied with trained flavor profile analysis panels and was proposed as an ideal odor reference standard to be used for training and sensory assessment of water samples. Main focus was to understand metallic flavor of drinking water caused by iron and copper. It was shown that metallic sensation has taste and retronasal components creating the flavor and humans are very sensitive to it. Occurrence of lipid oxidation in the oral cavity was shown when metals were ingested, that produces carbonyls which are responsible for the metallic flavor. Antioxidants and chelators were investigated to study prevention of lipid oxidation and, chelators were determined to be more effective. Oral epithelial cell cultures were developed as a model for oral cavity to further investigate lipid oxidation and effectiveness of the antioxidants and chelators. This dissertation is a result of inter-disciplinary work and possibly a good example for how problems may be solved by incorporating different methods and point of views from several disciplines.
Ph. D.
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43

Li, Bingbing. "Surface Characterization of Poly (epsilon-caprolactone) at the Air/Water Interface." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/10125.

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Surface behavior of poly (epsilon-caprolactone) (PCL) have been studied at the air/water interface (A/W). PCL is a hydrophobic and crystalline polyester with a glass transition temperature around -60 degrees centigrade, a melting point around 55 degrees centigrade, excellent biocompatibility, and low toxicity. In the past decade, PCL based systems have attracted considerable interest for controlled-release drug delivery and as scaffolds for tissue engineering, that require a fundamental understanding of PCL's degradation mechanisms and crystallization properties. PCL spherulites were commonly observed in previous bulk studies. This thesis focuses on PCL crystallization in Langmuir monolayers. Brewster angle microscopy (BAM) studies show that square, distorted rectangular, and dendritic crystals form at the A/W interface. While dendritic structures have been observed in poly (ethylene oxide) (PEO) thin film on solid substrates, this study of PCL is the first time that dendritic morphologies have been observed at the A/W interface for a linear flexible-coil polymer. As far as we know, the crystallization of flexible-coil polymers at the A/W interface is a brand new area of research. These findings may provide an interesting model system for studying crystallization in confined geometries and the effect of crystallinity on enzyme catalyzed hydrolysis of this important biodegradable polymer at the A/W interface. The main objectives of this thesis were to investigate the phase behavior of PCL at the A/W interface, gain a deeper understanding of the nucleation and growth mechanism of PCL crystallization at the A/W interface through surface pressure-area isotherms and isobaric area relaxation analyses, and interpret the effects of molecular weight on the nucleation and growth mechanism, and morphologies of semicrystalline PCL crystallized in Langmuir monolayers at the A/W interface.
Master of Science
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44

Dubreuil, Nicolas. "Etude de films mixtes d'acide gras et d'enzyme élaborés par la technique de Langmuir-Blodgett." Rouen, 1995. http://www.theses.fr/1995ROUES049.

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Le but de ce travail a été de caractériser des films mixtes acide gras/enzyme élaborés par la technique de Langmuir-Blodgett. L'acide gras utilisé est l'acide béhénique (AB) et l'enzyme est la glucose oxydase (GOx). Les études sur le film à l'interface eau/air (isothermes de compression, stabilité, hystérésis, microscopie à l'angle de Brewster) ont montré que l'enzyme s'adsorbait entre les molécules d'acide béhénique et sous le film, ce qui a pour effet de stabiliser le film. Ces études ont aussi permis de mettre au point un protocole d'élaboration du film mixte à l'interface. Les spectroscopies IR et UV-Vis ont permis de quantifier les deux espèces. La quantité d'enzyme déterminée indique que l'enzyme présente dans le film LB provient principalement de l'enzyme présente à l'interface, ce qui montre que les interactions AB/GOx sont faibles. La microscopie à force atomique montre qu'à l'échelle micrométrique, les échantillons préparés par les techniques de transferts vertical et horizontal sont hétérogènes. Les échantillons préparés sur graphite laissent apparaître des agrégats enzymatiques. A l'échelle nanométrique, nous avons observé l'arrangement des molécules de GOx présentant une organisation en quasi cristaux 2D et mis en évidence l'arrangement des molécules d'acide béhénique sur les molécules de GOx. Les échantillons préparés sur mica se caractérisent par la présence d'une monocouche d'acide béhénique et d'agrégats enzymatiques non recouverts par l'acide béhénique. Il apparaît que la structure des échantillons préparés sur mica est plus proche de la structure du film à l'interface eau/air que celle des échantillons préparés sur graphite
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45

Kölsch, Patrick. "Static and dynamic properties of soluble surfactants at the air/water interface." Phd thesis, Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2005/571/.

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Amphiphilic molecules contain a hydrophilic headgroup and a hydrophobic tail. The headgroup is polar or ionic and likes water, the tail is typically an aliphatic chain that cannot be accommodated in a polar environment. The prevailing molecular asymmetry leads to a spontaneous adsorption of amphiphiles at the air/water or oil/water interfaces. As a result, the surface tension and the surface rheology is changed. Amphiphiles are important tools to deliberately modify the interfacial properties of liquid interfaces and enable new phenomena such as foams which cannot be formed in a pure liquid.

In this thesis we investigate the static and dynamic properties of adsorption layers of soluble amphiphiles at the air/water interface, the so called Gibbs monolayers. The classical way for an investigation of these systems is based on a thermodynamic analysis of the equilibrium surface tension as a function of the bulk composition in the framework of Gibbs theory. However, thermodynamics does not provide any structural information and several recent publications challenge even fundamental text book concepts.

The experimental investigation faces difficulties imposed by the low surface coverage and the presence of dissolved amphiphiles in the adjacent bulk phase. In this thesis we used a suite of techniques with the sensitivity to detect less than a monolayer of molecules at the air-water interface. Some of these techniques are extremely complex such as infrared visible sum frequency generation (IR-VIS SFG) spectroscopy or second harmonic generation (SHG). Others are traditional techniques, such as ellipsometry employed in new ways and pushed to new limits. Each technique probes selectively different parts of the interface and the combination provides a profound picture of the interfacial architecture.

The first part of the thesis is dedicated to the distribution of ions at interfaces. Adsorption layers of ionic amphiphiles serve as model systems allowing to produce a defined surface charge. The charge of the monolayer is compensated by the counterions. As a result of a complex zoo of interactions there will be a defined distribution of ions at the interface, however, its experimental determination is a big scientific challenge. We could demonstrate that a combination of linear and nonlinear techniques gives direct insights in the prevailing ion distribution. Our investigations reveal specific ion effects which cannot be described by classical Poisson-Boltzmann mean field type theories.

Adsorption layer and bulk phase are in thermodynamic equilibrium, however, it is important to stress that there is a constant molecular exchange between adsorbed and dissolved species. This exchange process is a key element for the understanding of some of the thermodynamic properties. An excellent way to study Gibbs monolayers is to follow the relaxation from a non-equilibrium to an equilibrium state. Upon compression amphiphiles must leave the adsorption layer and dissolve in the adjacent bulk phase. Upon expansion amphiphiles must adsorb at the interface to restore the equilibrium coverage. Obviously the frequency of the expansion and compression cycles must match the molecular exchange processes. At too low frequencies the equilibrium is maintained at all times. If the frequency is too fast the system behaves as a monolayer of insoluble surfactants. In this thesis we describe an unique variant of an oscillating bubble technique that measures precisely the real and imaginary part of the complex dilational modulus E in a frequency range up to 500 Hz. The extension of about two decades in the time domain in comparison to the conventional method of an oscillating drop is a tremendous achievement. The imaginary part of the complex dilational modulus E is a consequence of a dissipative process which is interpreted as an intrinsic surface dilational viscosity. The IR-VIS SFG spectra of the interfacial water provide a molecular interpretation of the underlying dissipative process.


Amphiphile Moleküle vereinen zwei gegensätzliche Strukturelemente. Sie bestehen aus einer polaren oder ionischen Kopfgruppe und einem unpolaren Molekülteil, häufig einer Kohlenwasserstoffkette. Die vorliegende molekulare Asymmetrie bewirkt eine spontane Adsorption der Amphiphile an der Wasser/Luft Grenzschicht. Als Folge verändern sich Oberflächenspannung und Grenzflächenrheologie. Amphiphile Moleküle werden benutzt, um die Eigenschaften flüssiger Grenzflächen zu verändern und begegnen uns z.B. in Form von Seifen oder anderen waschaktiven Substanzen im täglichen Leben.

Der erste Teil dieser Doktorarbeit widmet sich der Verteilung von Ionen an geladenen flüssigen Grenzflächen. Adsorbtionsschichten ionischer Amphiphile bieten Modellsysteme zur Untersuchung dieses klassischen Bereiches der Kolloid- und Grenzflächenforschung. Durch die Adsorption der Amphiphile in der Grenzschicht werden definierte Oberflächenladungen erzeugt, welche durch die angrenzenden Gegenionen in der Sublage kompensiert werden.

In dieser Arbeit wird gezeigt, dass eine Kombination aus linearen und komplexen nichtlinearen optischen Methoden, die experimentelle Bestimmung der Verteilung der Gegenionen an geladenen Grenzflächen ermöglicht. Unsere Messungen zeigen ionenspezifische Effekte, die sich nicht in Reihenfolge des Periodensystems ordnen lassen. Insbesondere wurde ein Phasenübergang in der Verteilung der Gegenionen von einem Zustand, in dem sich die Ionen in der Sublage befinden, zu einem Zustand bestehend aus direkt kondensierten Ionen beobachtet. Dieser Phasenübergang geschieht innerhalb einer geringen Erhöhung der Oberflächenladung und lässt sich nicht mit klassischen Theorien beschreiben.

Der zweite Teil dieser Arbeit widmet sich der Stabilität von Schaumlamellen. Eine Schaumlamelle ist ein dünner Wasserfilm, der durch die Adsorption von oberflächenaktiven Molekülen an beiden Seiten stabilisiert wird. In Zusammenhang von Schäumen muss zwischen zwei Prozessen unterschieden werden: Der Schaumbildung und der Schaumstabilität. Die zugrundeliegenden Mechanismen der Schaumbildung sind weitestgehend verstanden, die der Schaumstabilität jedoch noch nicht.

Um die Stabilität von Schäumen zu untersuchen, müssen Nichtgleichgewichtszustände erzeugt und die anschließende Relaxation in das Gleichgewicht beobachtet werden. In dieser Arbeit wurde ein neues Verfahren entwickelt, welches es ermöglicht, das Elastizitätsmodul von Grenzflächen in einem Frequenzbereich von 1-500 Hz zu bestimmen. Dies bedeutet eine Erweiterung um zwei Dekaden gegenüber herkömmlichen Methoden. Die Idee ist denkbar einfach: In einer mit Flüssigkeit gefüllten Kammer wird über die Bewegung eines Piezos eine Luftblase in Schwingung versetzt und mit einem in der Kammer befindlichen Drucksensor die Schwingungsantwort der Blase aufgezeichnet. Unsere Untersuchungen zeigen, dass die Voraussetzung für die Ausbildung einer stabilen Schaumlamelle das Vorkommen einer intrinsischen Oberflächenviskosität ist. Eine anschauliche Erklärung verdeutlicht dies: Eine viskose Oberfläche ist in der Lage, eine eingehende Störung lokal zu dämpfen, im Gegensatz zu einer komplett elastischen Oberfläche, wo sich die Störung über die gesamte Schaumlamelle verbreiten kann.

Untersuchungen mittels der IR-VIS SFG Spektroskopie ergaben, dass die Struktur des Wassers bei der Beschreibung der Schaumstabilität auf molekularer Ebene eine entscheidende Rolle spielt: Die Oberflächenviskosität ist mit einem dissipativen Vorgang innerhalb der Grenzschicht verbunden. Dieser dissipative Vorgang konnte auf molekularer Ebene durch das Aufbrechen von Wasserstoffbrückenbindungen identifiziert werden. Ausschlaggebend war dabei der Austausch der adsorbierten Amphiphile in der Grenzfläche und der angrenzenden Sublage.

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46

Jochum, Mara Nikola [Verfasser]. "Simulations of amphiphilic peptides at the air-water interface / Mara Nikola Jochum." Mainz : Universitätsbibliothek Mainz, 2013. http://d-nb.info/1030598118/34.

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47

Herlina. "Gas transfer at the air-water interface in a turbulent flow environment." Karlsruhe : Univ.-Verl, 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976595842.

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48

Maltseva, Elena. "Model membrane interactions with ions and peptides at the air,water interface." Phd thesis, [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976724537.

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49

Kölsch, Peter. "Static and dynamic properties of soluble surfactants at the air, water interface." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976726548.

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50

Enright, Bryn Alison. "Adsorption of VOC vapors at the air-water interface in unsaturated media." Thesis, The University of Arizona, 1998. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0092_sip1_w.pdf&type=application/pdf.

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