Spehr, Tinka Luise (2010)
Water Dynamics In Soft Confinement - Neutron Scattering Investigations On Reverse Micelles.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
In the present experimental study we investigate the dynamical behaviour of water in soft confinement. As a model system we choose the AOT (sodium bis[ethylhexyl] sulfosuccinate) based water-in-oil droplet microemulsion which we precharacterize in detail. Using small angle neutron scattering we determine the microemulsion structure as a function of composition. Spherical water droplets (reverse micelles) coated by a monomolecular layer of the surfactant are dispersed in the continuous oil matrix. By variation of the molar ratio of water to surfactant one may control the droplet size between a few Angström and several nanometers. We extend the phase diagram to temperatures far below the freezing point of bulk water to determine the range of structural stability of the droplets as a function of water loading. The supercooling of the confined water is investigated by means of elastic fixed window scans on neutron backscattering. The freezing point of the confined water as well as the lower stability temperature decrease with decreasing droplet size. Moreover we use neutron- spin-echo spectroscopy to measure droplet diffusion and form fluctuations, whereof we deduce the temperature dependency of the bending modulus of the surfactant shell. The influence of confinement on the water mobility is then studied using two systems with different droplet sizes. We access the water dynamics over three orders of magnitude from pico- to nanoseconds by the combination of neutron backscattering and time-of-flight spectroscopy. We analyze the data taking into account rotation and jump diffusion. We find the water diffusion inside the droplets on average to be considerably slowed down with respect to bulk water. The translational mobility further decreases with decreasing droplet size. We extract values for rotational and translational diffusion coefficients. Dependent on water loading, two dynamically separated water fractions inside the droplets are resolved, one probably corresponding to surfactant bound water and the other one corresponding to less hindered water in the middle of the droplet core. We determine the absolute number of tightly bound water molecules per AOT molecule.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2010 | ||||
Autor(en): | Spehr, Tinka Luise | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Water Dynamics In Soft Confinement - Neutron Scattering Investigations On Reverse Micelles | ||||
Sprache: | Englisch | ||||
Referenten: | Stühn, Prof. Dr. Bernd ; Vogel, Prof. Dr. Michael | ||||
Publikationsjahr: | 3 Februar 2010 | ||||
Ort: | Darmstadt | ||||
Verlag: | Technische Universität | ||||
Datum der mündlichen Prüfung: | 25 Januar 2010 | ||||
URL / URN: | urn:nbn:de:tuda-tuprints-20403 | ||||
Kurzbeschreibung (Abstract): | In the present experimental study we investigate the dynamical behaviour of water in soft confinement. As a model system we choose the AOT (sodium bis[ethylhexyl] sulfosuccinate) based water-in-oil droplet microemulsion which we precharacterize in detail. Using small angle neutron scattering we determine the microemulsion structure as a function of composition. Spherical water droplets (reverse micelles) coated by a monomolecular layer of the surfactant are dispersed in the continuous oil matrix. By variation of the molar ratio of water to surfactant one may control the droplet size between a few Angström and several nanometers. We extend the phase diagram to temperatures far below the freezing point of bulk water to determine the range of structural stability of the droplets as a function of water loading. The supercooling of the confined water is investigated by means of elastic fixed window scans on neutron backscattering. The freezing point of the confined water as well as the lower stability temperature decrease with decreasing droplet size. Moreover we use neutron- spin-echo spectroscopy to measure droplet diffusion and form fluctuations, whereof we deduce the temperature dependency of the bending modulus of the surfactant shell. The influence of confinement on the water mobility is then studied using two systems with different droplet sizes. We access the water dynamics over three orders of magnitude from pico- to nanoseconds by the combination of neutron backscattering and time-of-flight spectroscopy. We analyze the data taking into account rotation and jump diffusion. We find the water diffusion inside the droplets on average to be considerably slowed down with respect to bulk water. The translational mobility further decreases with decreasing droplet size. We extract values for rotational and translational diffusion coefficients. Dependent on water loading, two dynamically separated water fractions inside the droplets are resolved, one probably corresponding to surfactant bound water and the other one corresponding to less hindered water in the middle of the droplet core. We determine the absolute number of tightly bound water molecules per AOT molecule. |
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Alternatives oder übersetztes Abstract: |
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Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 530 Physik | ||||
Fachbereich(e)/-gebiet(e): | 05 Fachbereich Physik > Institut für Festkörperphysik (2021 umbenannt in Institut für Physik Kondensierter Materie (IPKM)) 05 Fachbereich Physik |
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Hinterlegungsdatum: | 15 Feb 2010 09:31 | ||||
Letzte Änderung: | 05 Mär 2013 09:31 | ||||
PPN: | |||||
Referenten: | Stühn, Prof. Dr. Bernd ; Vogel, Prof. Dr. Michael | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 25 Januar 2010 | ||||
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