133 research outputs found
Bestimmung und Beeinflußung von lateralen und vertikalen Eigenschaften von Polyelektroltymultischichten
No full textDiese Dissertation präsentiert experimentelle Untersuchungen zu vertikalen und lateralen Strukturen von Polyelektrolytmultischichten (PEM) adsorbiert auf festen Oberflächen. Zur Herstellung von PEM werden Polykationen (Poly-(allylamin)hydrochlorid (PAH) oder Poly-(diallyldimethylammonium)chlorid, PDADMAC) und Polyanionen (Polys-(styren)sulfonat (PSS)) aus einer wässrigen Lösung auf eine hydrophile Siliziumdioxid-Oberfläche sequentiell adsorbiert. Um nicht–elektrostatische (sekundäre) Kräfte während der Adsorption zu untersuchen, wird Reichweite und Stärke der elektrostatischen Wechselwirkung durch eine definierte Konzentration monvalenten Salzes (c_ads) in den Polyelektrolyt (PE)-Lösungen eingestellt. Schichtdicke, und Homogenität der Multischichten entlang der PEM-Normalen werden mit Röntgenreflexion gemessen. Dies ist in Übereinstimmung mit veröffentlichten Daten und wird auf die elektrostatische Abschirmung, beschrieben durch die Debye-Hückel Theorie zurückgeführt. Komplementär wird Neutronenreflexion genutzt, um die Interpenetration einzelner Polyelektrolytschichten zu quantifizieren. Hierzu wird ein PEM aus zwei Blöcken unterschiedlicher Streulängendichte (SLD) hergestellt. Der SLD-Kontrast wird durch Verwendung von protonierten und deuterierten PSS realisiert. Durch Variation der Anzahl protonierter und deuterierter PE-Schichten wird die Breite der inneren Grenzflächen positionsabhängig entlang der PEM-Normalen vermessen. So ist erstmals eine eindeutige Bestimmung der Interpenetration (inneren Rauigkeit, sigma_int) benachbarter Polykat-/Polyananiondoppelschichten möglich. Die PEM-Dicke skaliert mit der Wurzel der Salzkonzentration in der Adsorptionslösung. Sowohl für PAH/PSS als auch für PDADMAC/PSS-Multischichten ist sigma_int nahe an der Film/Luft-Grenzfläche am geringsten und steigt mit zunehmendem Abstand. Für das PAH/PSS-System ist die Zunahme monoton, während beim PDADMAC/PSS-System sigma_int zunächst anwächst und sich dann eine konstante innere Rauigkeit (sigma_int, max) einstellt. Bei PADMAC/PSS steigt sigma_int,max mit zunehmendem c_ads. Erklärt wird diese Beobachtung durch eine höhere extrinsische Ladungsträgerkompensation der Polyelektrolytketten und eine verringerte elektrostatische Wechselwirkung, letzteres führt zu einer erhöhten Flexibilität der Polyelektrolytketten. Die Änderung von sigma_int wird über ein 1-dimensionales Diffusionsmodell quantifiziert. Zusätzlich wird der Polymerisationsgrad (Anzahl Monomere pro Kette) des Polykations variiert. Bei einer Vergrößerung des Polymerisationsgrades und großem c_ads nimmt die maximale innere Rauigkeit ebenfalls zu. Dies weist auf kooperative Effekte zwischen Polykat- und Polyanion hin, da nur das PSS deuteriert ist. Bei geeignetem c_ads nimmt die Dicke pro adsorbierter Polykation/Polyanion-Doppelschicht (d_Bl) zu. Während für den salzfreien Fall (c_ads = 0) die Parameter d_Bl und Polymerisationsgrad entkoppelt sind, wird die Kopplung mit steigendem c_ads immer deutlicher. Dies wird mit einer PE-Schicht erklärt, in der die PE-Ketten bei der Adsorption eine flache (c_ads = 0) bzw. geknäulte (c_ads > 0) Konformation einnehmen. In diesem Fall steigt sigma_int bei großem Polymerisationsgrad rapide nahe der PEM/Luft-Grenzfläche, d.h. die Diffusionskonstante wächst. An dieser Stelle wird die These aufgestellt, daß entropische Kräfte und Stressrelaxation die Interpenetration verursachen. sigma_int, max stellt einen metastabilen Gleichgewichtszustand dar. Da die Diffusionskonstante einer Kette invers mit der Anzahl der Segmente skaliert, erklärt Stressrelaxation warum die Diffusionskonstante mit steigendem Polymerisationsgrad zunimmt.This thesis represents experimental investigations of vertical and lateral structures of polyelectrolyte multilayer (PEMs) adsorbed on solid surfaces. PEMs are prepared by sequential adsorption of dissolved polycations (poly-(allylamine) hydrochloride (PAH) or poly-(diallyldimethylammonium) chloride (PDADMAC)) and polyanions (poly-(styrenesulfonate) sodium salt (PSS)). In order to investigate secondary (non-electrostatic) forces during the absorption process, a defined concentration of monovalent salt (c_ads) in the absorption solution is used to control range and strength of electrostatic interactions. PEM thickness and homogeneity are explored by x-ray reflectivity. The PEM thickness scales with the square root of c_ads. This is in agreement with other published data and can be described by the Debye-Hückel theory. To quantify the interdigitation of adjacent polycation/ polyanion layer pairs (inner roughness) neutron reflection is used as a complementary technique. Each PEM consists of a protonated and a deuterated block. The contrast in the scattering length density (SLD) is realized by deuterated PSS. The total amount of adsorbed bilayers is kept constant while the position of the interface between the protonated and deuterated block is varied systematically. This approach enables the investigation of selected inner interfaces of PEMs for the first time. For both the PAH/PSS- and the PDADMAC/PSS multilayers, the inner roughness (sigma_int) next to the air/film surface is smallest and increases with distance from the film/air interface. In detail, sigma_int grows for PAH/PSS-multilayers monotonically, while for PEMs built from PDADMAC and PSS a constant inner roughness (sigma_int, max) in the centre of the PEM is found. For the centre of PDADMA/PSS films, the width of the inner interface (sigma_int, max) increases with c_ads. This behavior is explained by a higher degree of extrinsic charge compensation and an increased electrostatic shielding. Thus a decrease of attractive polyanion/polycation interaction results, which in turn leads to an increased polyelectrolyte flexibility. The change of sigma_int is quantified with a 1-dimensional diffusion process. Furthermore an increase in the sigma_int, max is observed by increasing the degree of polymerization of PDADMAC. Due to the fact that only the polyanions give a contrast in the SLD-profile, cooperative effects take place. The thickness per adsorbed bilayer (d_Bl) scales with the degree of polymerization of PDADMAC, if c_ads is suitable. If c_ads = 0 (salt free) d_Bl is independent of degree of polymerization, while by increasing c_ads the dependency of d_Bl on the degree of polymerization gets more pronounced. This is explained by different conformations during the adsorption (flat if c_ads = 0 and more coiled if c_ads > 0). Furthermore, the diffusion constant is higher for PEMs made of PDADMAC with llarger degree of polymerization. To explain this finding it is proposed that entropy gain and stress relaxation cause the interpenetration of adjacent bilayers. In fact the polycation/polyanion bilayer in the centre of the PEM represent a metastable state where the chains are partly relaxed. Given that the diffusion constant is inversely proportional to the degree of polymerization, an increased change in the inner roughness due to longer chains has to be attributed to stress relaxation
Pigments of sediment cores of the Northwest European Continental Margin
No full textIn the context of the European OMEX Programme this investigation focused on gradients in the biomass and activity of the small benthic size spectrum along a transect across the Goban Spur from the outer Celtic Sea into Porcupine Abyssal Plain. The effects of food pulses (seasonal, episodic) on this part of the benthic size spectrum were investigated. Sediments sampled during eight expeditions at different seasons covering a range from 200 m to 4800 m water depth were assayed with biochemical bulk measurements: determinations of chloroplastic pigment equivalents (CPE), the sum of chlorophyll a and its breakdown products, provide information concerning the input of phytodetrital matter to the seafloor; phospholipids were analyzed to estimate the total biomass of small benthic organisms (including bacteria, fungi, flagellata, protozoa and small metazoan meiofauna). A new term 'small size class biomass' (SSCB) is introduced for the biomass of the smallest size classes of sediment-inhabiting organisms; the reduction of fluorescein-di-acetate (FDA) was determined to evaluate the potential activity of ester-cleaving bacterial exoenzymes in the sediment samples.
At all stations benthic biomass was predominantly composed of the small size spectrum (90% on the shelf; 97–98% in the bathyal and abyssal parts of the transect). Small size class biomass (integrated over a 10 cm sediment column) ranged from 8 g C/m**2 on the shelf to 2.1 g C/m**2 on the adjacent Porcupine Abyssal Plain, exponentially decreasing with increasing water depth. However, a correlation between water depth and SSCB, macrofauna biomass as well as metazoan meiofauna biomass exhibited a significantly flatter slope for the small size classes in comparison to the larger organisms.
CPE values indicated a pronounced seasonal cycle on the shelf and upper slope with twin peaks of phytodetrital deposition in mid spring and late summer. The deeper stations seem to receive a single annual flux maximum in late summer. SSCB and heterotrophic activity are significantly correlated to the amount of sediment-bound pigments. Seasonality in pigment concentrations is clearly followed by SSCB and activity. In contrast to macro- and megafauna which integrate over larger periods (months/years), the small benthic size classes, namely bacteria and foraminifera, proved to be the most reactive potential of the benthic communities to any perturbations on short time scales (days/weeks). The small size classes, therefore, occupy a key role in early diagenetic processes
Biogeochemical investigation of surface sediments from the Atlantic
No full textBiogeochemical investigation of surface sediments from the Atlanti
Biochemical investigation of sediment core D204_MUC1
No full textBiochemical investigation of sediment core D204_MUC
The size structure of deep-sea meiobenthos in the North-Eastern Atlantic: Nematode size spectra in relation to environmental variables
No full textThe size distribution of benthic nematodes was investigated along different gradients of food availability in various regions of the NE Atlantic: I. across the continental margin and II. with increasing distance from the continental rise. An overall trend for miniaturization with increasing distance from the food source was found. However, a series of physical, chemical and biological factors clearly lead to variations in nematode size structure. Moreover, our results indicate that seasonally varying food supply or a periodically pulsed input of organic matter to the sea floor affects nematode size spectra. The hypothesis is proposed that the life cycle of deep-sea nematode species and hence the size structure of their populations are related to seasonal energy availability. This dependence might result in one-year life spans of deep-sea nematodes and probably other meiofauna
Small benthic size classes along the NW European Continental Margin: spatial and temporal variability in activity and biomass
No full textIn the context of the European OMEX Programme this investigation focused on gradients in the biomass and activity of the small benthic size spectrum along a transect across the Goban Spur from the outer Celtic Sea into Porcupine Abyssal Plain. The effects of food pulses (seasonal, episodic) on this part of the benthic size spectrum were investigated. Sediments sampled during eight expeditions at different seasons covering a range from 200 m to 4800 m water depth were assayed with biochemical bulk measurements: determinations of chloroplastic pigment equivalents (CPE), the sum of chlorophyll a and its breakdown products, provide information concerning the input of phytodetrital matter to the seafloor; phospholipids were analyzed to estimate the total biomass of small benthic organisms (including bacteria, fungi, flagellata, protozoa and small metazoan meiofauna). A new term `small size class biomass' (SSCB) is introduced for the biomass of the smallest size classes of sediment-inhabiting organisms; the reduction of fluorescein-di-acetate (FDA) was determined to evaluate the potential activity of ester-cleaving bacterial exoenzymes in the sediment samples.
At all stations benthic biomass was predominantly composed of the small size spectrum (90% on the shelf; 97–98% in the bathyal and abyssal parts of the transect). Small size class biomass (integrated over a 10 cm sediment column) ranged from 8 g C m−2 on the shelf to 2.1 g C m−2 on the adjacent Porcupine Abyssal Plain, exponentially decreasing with increasing water depth. However, a correlation between water depth and SSCB, macrofauna biomass as well as metazoan meiofauna biomass exhibited a significantly flatter slope for the small size classes in comparison to the larger organisms.
CPE values indicated a pronounced seasonal cycle on the shelf and upper slope with twin peaks of phytodetrital deposition in mid spring and late summer. The deeper stations seem to receive a single annual flux maximum in late summer. SSCB and heterotrophic activity are significantly correlated to the amount of sediment-bound pigments. Seasonality in pigment concentrations is clearly followed by SSCB and activity. In contrast to macro- and megafauna which integrate over larger periods (months/years), the small benthic size classes, namely bacteria and foraminifera, proved to be the most reactive potential of the benthic communities to any perturbations on short time scales (days/weeks). The small size classes, therefore, occupy a key role in early diagenetic processes
NREX: Neutron reflectometer with X-ray option
No full textThe high resolution neutron/ X-ray contrast reflectometer NREX, operated by the Max Planck Institute for Solid State Research, is designed for the determination of structural and magnetic properties of surfaces, interfaces, and thin film systems
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