Stabilität adsorbierter Polymerschichten an Grenzflächen

Note: This is an updated version of the original thesis (https://opus4.kobv.de/opus4-fau/frontdoor/index/index/docId/2844) The adsorption of P123 at the solid-liquid interface is investigated under various conditions (temperature, concentration, shear) using time-of-flight neutron reflectivity. Different types of adsorption can be shown to exists. Several slabs are adsorbed on top of the native Si oxid layer. Their adsorption varies with temperature and concentration, with the layers slightly affected by shear. These layers are denoted as intermediate layers. In addition, a Bragg reflection was observed in the temperature range between 48°C and 64 °C. This reflectivity profile is successfully fitted using the assumption of a periodic structure. Up to now, such crystallization was reported for high concentrations only. In SAXS measurements it was not possible to investigate such a bulk agglomeration due to the diluted solutions used in this work. Therefore, the surface crystallization is affected by the liquid-solid boundary. If the radii of the micelles are compared with the periodicity of the multi-layers, the alignment of micelles to a structured multi layer appears. A comparison between the fcc cell parameter measured at high concentration and the repetition length shows an increased distance between the individual micelles. This is an indication for a weaker intermicellar bonding. It has to be noted when only specular reflectometry is used it is not possible to distinguish an alignement of micelles (cylindrical or spherical) from the formation of a lamellar layer. Additionally, the effect of shear was investigated in this thesis. In concentrated solutions a difference could be shown in the relaxation behavior for the cubic or the hexagonal phase. Analyzing the Bragg intensity for the diluted solutions results in a Sigmoidal adsorption isotherme. Such an adsorption isotherme is known to exist in systems with a coupling in between the adsorbants. A spontaneous adsorption of a micelle in the beginning favors the attachment of further micelles. In these measurements a strong correlation between the ordering and temperature, concentration and substrate could be shown. In general, ordering increases considerably when shear is applied. This is in contrast to concentrated solutions. All measurements after the application of shear also indicate a lower periodicity. Possibly the lower intermicellar bonding can be attributed to these effects. Additionally two different timescales are observed during the analysis of the relaxation measurements. At a concentration of 10 wtp this change of relaxation type becomes dominant. A possible interpretation is a change of the structure within the adsorbed multi-layer. Thus, at lower concentrations the adsorbtion of micelles is favored as compared to a lamellar structure at high concentrations. Further, the periodicity decreases with rising temperature for all concentrations except 10 wtp. This shrinking of the layer distance may be affected by the decrease of hydration especially for the PPO block. The fact that such changes do not show for the 10 wtp solutions strengthens the assumption of a lamellar layer in this case. Using all points previously discussed a phasediagram can be drawn for adsorbed P123. Above an OTS coated and therefore hydrophobic Si substrate an adsorbed P123 layer was found. In contrast to the hydrophilic Si substrate the adsorbates did not change after applying shear. The layers are only affected by changes in concentration and temperature. Further GISANS measurements and reflectometry with an increased Q-range can reveal the structure of the adsorbed intermediate layers. It would be highly interesting to use concentrations even lower than the critical micellization concentration to allow direct measurements of the adsorbed intermediate layers.Hinweis: Dies ist eine überarbeitete Version der ursprünglichen Dissertation (https://opus4.kobv.de/opus4-fau/frontdoor/index/index/docId/2844) Im Rahmen dieser Promotionsarbeit konnte die Komplexität der Adsorption von P123 an der fest-flüssig Grenzfläche gezeigt werden. Dabei kann generell zwischen verschiedenen Arten der Adsorption unterschieden werden. Zum einen gibt es mehrere Schichten oberhalb des natürlichen Si-Oxids, die sowohl von der Temperatur als auch der Konzentration abhängig sind, durch Scherung jedoch nur gering beeinflusst werden. Diese werden im weiteren als Zwischenschichten bezeichnet. Zum anderen wurde im Temperaturbereich von 48 °C bis 64 °C die Ausbildung eines Bragg Reflexes, also eines Mehrschichtsystems, beobachtet. Es war möglich, die Reflektivität durch die Annahme einer periodischen Struktur anzunähern und die Periodizität zu bestimmen. Solch eine Kristallisation wurde bisher nur bei hohen Konzentrationen beobachtet. Bei solch niedrigen Konzentrationen ist dies ein reiner Oberflächeneffekt, da sonst auch in SAXS Messungen bei Q=0.05 Å^-1 eine konstruktive Interferenz festzustellen wäre. Eine Betrachtung der Mizellendurchmesser zeigt, dass eine regelmäßige Anordnung von Mizellen denkbar ist. Ob es sich bei der Oberflächenkristallisation jedoch um die strukturierte Anordnung von Mizellen (kugelförmig oder auch zylindrisch), oder um ein lamellares System handelt, kann anhand der durchgeführten Messungen generell nicht unterschieden werden. Wird zusätzlich die Wiederholperiode aus den Reflektivitätsmessungen mit dem fcc Gitterparameter der konzentrierten Lösung verglichen, weist die verdünnte Lösung einen größeren Abstand zwischen den einzelnen Schichten auf, was ein Indiz für eine schwächere intermizellare Bindung sein könnte. Zusätzlich wurde die Auswirkung von Scherung auf die angelagerten Schichten bei geringer Konzentration untersucht, da bereits an konzentrierten Lösungen im Bereich der kubischen und hexagonalen Phase Unterschiede in der Relaxation beobachtet wurden. Eine Analyse der integralen Bragg Intensität zeigt sehr deutlich eine Sigmoidale Adsorptionsisotherme, welche auf Kopplungseffekte zwischen den Mizellen hinweist. Eine solche Adsorptionsisotherme entsteht, wenn durch die anfänglich spontane Adsorption die Anlagerung weiterer Mizellen begünstigt wird. Hier offenbarte sich eine sehr starke Abhängigkeit sowohl von Temperatur und Konzentration als auch von der Grenzfläche. Generell ist es auffällig, dass die Ordnung durch Scherung immer stark verbessert wird, im Gegensatz zu den Messungen konzentrierter P123 Lösungen. Möglicherweise steht dies in Wechselwirkung zu der schwächeren intermizellaren Bindung, da sich nach Scherung auch die Wiederholperiode im Vergleich zu den statischen Messungen tendenziell erniedrigt. Die Auswertung der Relaxationsmessungen gibt zusätzlich einen Hinweis auf zwei unterschiedliche Zeitskalen für die Relaxation. Dies kann als Unterschied zwischen der strukturierten Anordnung von Mizellen und der lamellaren Anordnung interpretiert werden; vorwiegend ab einer Konzentration von 10 wtp. Eine Betrachtung der Wiederholperiode zeigt, dass für alle Konzentrationen -- bis auf 10 wtp -- der Abstand zwischen den einzelnen Schichten mit höherer Temperatur sinkt. Die sinkende Hydratation des Polyethers als Funktion der Temperatur könnte dafür eine Erklärung sein. Solch ein Verhalten kann jedoch nicht bei der 10 wtp P123 Lösung festgestellt werden, was die Vermutung einer lamellaren Adsorption weiter festigt. Somit ist es möglich, ein Phasendiagramm zu erstellen, welches die verschiedenen Adsorptionsarten als Funktion der Temperatur und Konzentration zusammenfasst. Oberhalb eines mit OTS beschichteten, hydrophoben Si Substrats konnte in den statischen Messungen eine adsorbierte Schicht P123 festgestellt werden. Diese zeigt jedoch keine Änderung durch das Anlegen von Scherung und war rein konzentrations- und temperaturabhängig. Weiterführende Arbeiten könnten durch GISANS oder anhand von Messungen der Reflektivität in einem größerem Q-Bereich zusätzliche Information über diese Zwischenschichten liefern und die genaue laterale Struktur aufklären. Des Weiteren wäre der Übergang zu noch niedrigeren Konzentrationen hochinteressant, so dass die Konzentration für die Bildung von Mizellen nicht mehr ausreichend ist und somit ein direkter Zugang zu diesen Zwischenschichten ermöglicht wird

Soil colloids as binding agents in the formation of soil microaggregates in wet-dry cycles: A case study for arable Luvisols under different management

In the hierarchical model of soil aggregates, small soil microaggregates (small SMA; 40 μm up to 1700 μm in maximum. Our study on aggregation in wet-dry cycles revealed that the colloidal content has a controlling effect on the size distribution of resulting aggregates by acting as a binding agent and provides hereby new insights into the evolvement of aggregate hierarchy in soils

Cache-oblivious dynamic dictionaries with update/query tradeoffs

Several existing cache-oblivious dynamic dictionaries achieve O(logB N) (or slightly better O(logB N over M )) memory transfers per operation, where N is the number of items stored, M is the memory size, and B is the block size, which matches the classic B-tree data structure. One recent structure achieves the same query bound and a sometimes-better amortized update bound of O (...) memory transfers. This paper presents a new data structure, the xDict, implementing predecessor queries in O(...)worstcase memory transfers and insertions and deletions in O (...) amortized memory transfers, for any constant " with 0 < epsilon < 1. For example, the xDict achieves subconstant amortized update cost when N = ..., whereas the B-tree’s ... is subconstant only when ... is subconstant only when N = .... The xDict attains the optimal tradeoff between insertions and queries, even in the broader external-memory model, for the range where inserts cost between (...) and O(1= lg3 N) memory transfers.Danish National Research Foundation (MADALGO (Center for Massive Data Algorithmics))National Science Foundation (U.S.) (NSF Grants CCF-0541209)National Science Foundation (U.S.) (NSF Grants CCF-0541209)Computing Innovation Fellow

Copper oxide nanoparticles induce oxidative stress, DNA strand breaks and laccase activity in aquatic fungi

This work was supported by the DAAD-FCT-2010-2011 project (Micro)analysis of nanoparticles on aquatic fungi and A. Pradhan received the FCT grant SFRH/BD/45614/2008

Responses of freshwater microbial decomposers to copper oxide nanoparticles

Intensive use of nano metals increases the chance of their release into natural watercourses and may pose at risk aquatic biota and their ecological functions. In streams, microbial decomposers, predominantly aquatic fungi, play a crucial role in organic matter turnover. We investigated the impact of nano CuO on stream-dwelling microbial decomposers of leaf litter by examining i) structure and functions of fungal and bacterial communities retrieved from a non-polluted stream, and ii) the physiological and cellular responses of fungal populations isolated from metal-polluted and non-polluted streams. Results were compared to those obtained after exposure to Cu2+. The exposure to nano CuO (≤500 ppm, 4 levels) and Cu2+ (≤30 ppm, 4 levels) significantly reduced leaf decomposition, bacterial and fungal biomass, fungal reproduction and diversity. Cluster analysis of DGGE based on DNA fingerprints showed that both forms of copper induced shifts in community structure. However, impacts were stronger for bacteria than fungi. At the cellular level, increased nano CuO concentrations (≤200 ppm, 5 levels) induced activity of laccase by single fungal populations. Fungal populations from non-polluted streams were more affected by nano CuO than those from polluted streams, as shown by stronger inhibition of biomass production, accumulation of reactive oxygen species (ROS), plasma membrane disruption and DNA strand breaks. Results showed that nano forms are less toxic than ionic forms, and further suggest that the toxicity of nano CuO to freshwater microbial decomposers may occur due to induction of oxidative stress.FEDER-POFC-COMPETE and FCT supported this study (PEst-C/BIA/UI4050/2011, PTDC/AAC- AMB/121650/2010 and FCT-DAAD: 2010-2011) and AP (SFRH/BD/45614/2008)

Effects of nano CuO on aquatic decomposers: from community to cellular responses

ntensive use of metal nanoparticles increases the chance of their release into freshwaters that may pose risk to biota and associated ecological processes. In streams, microbes play a key role in detritus foodwebs transferring carbon and energy from plant litter to invertebrate shredders. Here, we investigated the effects of nano CuO (<50 nm, nanopowder, Sigma) on aquatic detritus foodwebs by examining i) leaf-litter decomposition by bacterial and fungal communities, ii) cellular damage and physiological responses of fungal populations collected from non-polluted and metal-polluted streams, and iii) survival, growth and leaf consumption by an invertebrate shredder. Results were compared with those obtained with ionic copper. Stream-dwelling microbial communities were obtained by immersion of leaves in a non- polluted stream (Portugal). Microbial communities were exposed in microcosms to nano CuO (≤ 500 mg L-1) and Cu2+ (≤ 30 mg L-1). Leaf decomposition decreased with increasing concentrations of nano and ionic copper. Both copper forms reduced biomass of bacteria and fungi, and fungal reproduction. Cu2+ had stronger effects than nano CuO. Exposure to Cu2+ and nano CuO led to a decrease in fungal diversity and to shifts in species dominance. Increased concentrations of nano CuO (≤ 100 mg L–1) stimulated extracellular laccase activity by fungi. Populations from non-polluted streams were more affected by nano CuO than those from polluted streams, as shown by a stronger inhibition of biomass production, higher Cu adsorption, higher levels of reactive oxygen species and DNA strand breaks. Acute lethality tests suggested low toxicity of nano CuO to the shredder Allogamus ligonifer. However, sublethal concentrations of nano CuO (≤ 75 mg L–1) strongly reduced leaf consumption and invertebrate growth under aqueous and dietary exposure. Concentration of leached Cu2+ in the stream water increased with increasing nano CuO concentration. Exposure to 75 mg L–1 of nano CuO via water or food led to higher Cu adsorption and accumulation in larvae. Moreover, leached Cu2+ appeared to have a role in inducing toxicity of nano CuO.Acknowledgement: FEDER-POFC-COMPETE, DAAD and FCT supported this work (PEst-C/BIA/UI4050/2011, FCT-DAAD-2010-2011, NANOECOTOX-PTDC/AAC-AMB/121650/2010) and A. Pradhan (SFRH/BD/45614/2008)

Exploring Flood Filling Networks for Instance Segmentation of XXL-Volumetric and Bulk Material CT Data

XXL-Computed Tomography (XXL-CT) is able to produce large scale volume datasets of scanned objects such as crash tested cars, sea and aircraft containers or cultural heritage objects. The acquired image data consists of volumes of up to and above 10,0003 voxels which can relate up to many terabytes in file size and can contain multiple 10,000 of different entities of depicted objects. In order to extract specific information about these entities from the scanned objects in such vast datasets, segmentation or delineation of these parts is necessary. Due to unknown and varying properties (shapes, densities, materials, compositions) of these objects, as well as interfering acquisition artefacts, classical (automatic) segmentation is usually not feasible. Contrarily, a complete manual delineation is error-prone and time-consuming, and can only be performed by trained and experienced personnel. Hence, an interactive and partial segmentation of so-called “chunks” into tightly coupled assemblies or sub-assemblies may help the assessment, exploration and understanding of such large scale volume data. In order to assist users with such an (possibly interactive) instance segmentation for the data exploration process, we propose to utilize delineation algorithms with an approach derived from flood filling networks. We present primary results of a flood filling network implementation adapted to non-destructive testing applications based on large scale CT from various test objects, as well as real data of an airplane and describe the adaptions to this domain. Furthermore, we address and discuss segmentation challenges due to acquisition artefacts such as scattered radiation or beam hardening resulting in reduced data quality, which can severely impair the interactive segmentation results

Ultra-fast detector for wide range spectral measurements

KALYPSO is a novel detector operating at line rates above 10 Mfps. The detector board holds a silicon or InGaAs linear array sensor with spectral sensitivity ranging from 400 nm to 2600 nm. The sensor is connected to a cutting-edge, custom designed, ASIC readout chip which is responsible for the remarkable frame rate. The FPGA readout architecture enables continuous data acquisition and processing in real time. This detector is currently employed in many synchrotron facilities for beam diagnostics and for the characterization of self-built Ytterbium-doped fiber laser emitting around 1050 nm with a bandwidth of 40 nm