Not available / text

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Proefschrift Rijksuniversiteit Groningen. / Datum laatste controle: 23-10-1997. Lit.opg. - Met een samenvatting in het Nederlands.

No description available.

Ulm, Univ. Diss., 2006.

As the most important materials in civil engineering, bituminous and cementitious materials have been used widely in pavements and constructions for many years. Accurate determination of adhesion is important to the bonding properties of bituminous and cementitious materials. In this work, we presented a novel approach to measure the adhesion between binders and aggregate mineral particles at microscopic scale. Particle probe scanning force microscopes (SFM) were used to study the adhesion between mineral microspheres representing the primary aggregate constituents (Al2O3, SiO2 and CaCO3) and various control (PG 64-22 and PG 58-22) and modified binders. Results showed that these modified SFM probes could effectively measure the adhesion between binders and aggregate minerals. Consistent adhesion measurements were obtained between different asphalt binders and aggregate mineral particles. Statistical analyses were performed to evaluate effects of different factors on the aggregate-modified binder adhesion, including aggregate constituents, binder types, modifier types and cantilever properties. Due to the stronger polarity of alumina particles, stronger interactions occur within alumina-binder pairs than within silica- and calcium carbonate-binder pairs. Meanwhile, morphologies of different modified binders clearly demonstrated microstructural variations in these binders. The adhesion between steel and different cement hydrated products was measured using particle probe SFM. Adhesive forces are collected between steel microspheres and new (four-week old) and old (six-month old) cement in air and saturated lime water. Mixed Gaussian models were applied to predict phase distributions in the cement paste, i.e., low density C-S-H, high density C-S-H, CH, other hydrated products and the unreacted components. For new cement in saturated lime water, adhesive forces between steel and low density C-S-H, high density C-S-H and other hydrated products are intermediate among all groups selected. The adhesive forces between steel and calcium hydroxide are smallest, whereas the adhesive forces between steel and the unreacted phases are largest. For the six-month old cement, the interweaving of calcium carbonate crystals and C-S-H during the carbonation produces greater adhesive forces to steel, consistent with the adhesive forces between steel and the control calcium carbonate specimen. CH turned into calcium carbonate by reacting with carbon dioxide in air. An increase in adhesive forces was found between steel and calcium carbonate in the old cement than those between steel and CH in the new cement. Particle probe SFM is able to measure the adhesion in bimaterials. For bituminous materials, this methodology provides opportunities to evaluate the effects of different processing methods and to generate quantitative information for the development of multi- scale asphalt mixture cracking models. For cementitious materials, these studies opened new avenues to study the interactions between steel and cement at microscale under a variety of environmental conditions and can be formulated as crack initiation and propagation criteria incorporated in multiscale models for reinforced concrete structures.

Magnetic force microscopy (MFM) is a widely-used technique for measuring the local magnetic properties of a variety of materials. This method covers a large fi eld of applications ranging from fundamental research of micro-magnetic phenomena to industrial applications in the development of magnetic recording components. The image formation in MFM measurements is based on the magneto-static interaction of a sharp magnetic tip with the probed sample. Despite the fact that MFM is quite easy to perform, image interpretation remains challenging. This is due to the accurate characterization of the probing tip that is needed for a quantitative interpretation of the MFM data in terms of the local magnetic properties of the sample. This thesis examines the fabrication and utilization of special MFM probes based on single ferromagnetic nanoparticles as the magnetically interacting element. A magnetic probe that consists of a very small magnetic single-domain particle can be accurately described by a magnetic point dipole. Such a probe potentially yields an improved lateral resolution and a simplifi ed quantitative interpretation of MFM images compared to a standard thin-fi lm coated MFM tip. First of all, one part of this thesis examines the fabrication of suitable single-domain particles. In particular, this part is focussed on experiments concerning the protection of these particles from oxidation in ambient conditions. To this end, these ferromagnetic particles were coated with gold using the light-induced deposition of gold in a photoactive metal-salt solution. The chemical surface passivation of the particles by the gold coating was verifi ed using diff erent techniques (SQUID, MFM). In the next step, these particles were mechanically affi xed to a standard silicon tip of atomic force microscopy (AFM). The controlled attachment of a single particle, as well as the attachment of multiple particles to such a Si-AFM tip was demonstrated. Another part of the thesis examines the magnetic imaging with particle based probes in MFM experiments. A minimum of four cobalt particles affi xed to the tip was determined as the threshold for obtaining a reasonable MFM signal. It was possible to image the magnetic domain structure of a hard disk drive sample with these particle probes. Using a simulation of the MFM data, the orientation and the position of the e ffective tip dipole were determined. The e ffective dipole moment of the tip is found by a calibration experiment assuming a magnetic dipole-dipole interaction between the tip and another magnetic particle.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 117-131).

Magnetic force microscopy (MFM) is a widely-used technique for measuring the local magnetic properties of a variety of materials. This method covers a large fi eld of applications ranging from fundamental research of micro-magnetic phenomena to industrial applications in the development of magnetic recording components. The image formation in MFM measurements is based on the magneto-static interaction of a sharp magnetic tip with the probed sample. Despite the fact that MFM is quite easy to perform, image interpretation remains challenging. This is due to the accurate characterization of the probing tip that is needed for a quantitative interpretation of the MFM data in terms of the local magnetic properties of the sample. This thesis examines the fabrication and utilization of special MFM probes based on single ferromagnetic nanoparticles as the magnetically interacting element. A magnetic probe that consists of a very small magnetic single-domain particle can be accurately described by a magnetic point dipole. Such a probe potentially yields an improved lateral resolution and a simplifi ed quantitative interpretation of MFM images compared to a standard thin-fi lm coated MFM tip. First of all, one part of this thesis examines the fabrication of suitable single-domain particles. In particular, this part is focussed on experiments concerning the protection of these particles from oxidation in ambient conditions. To this end, these ferromagnetic particles were coated with gold using the light-induced deposition of gold in a photoactive metal-salt solution. The chemical surface passivation of the particles by the gold coating was verifi ed using diff erent techniques (SQUID, MFM). In the next step, these particles were mechanically affi xed to a standard silicon tip of atomic force microscopy (AFM). The controlled attachment of a single particle, as well as the attachment of multiple particles to such a Si-AFM tip was demonstrated. Another part of the thesis examines the magnetic imaging with particle based probes in MFM experiments. A minimum of four cobalt particles affi xed to the tip was determined as the threshold for obtaining a reasonable MFM signal. It was possible to image the magnetic domain structure of a hard disk drive sample with these particle probes. Using a simulation of the MFM data, the orientation and the position of the e ffective tip dipole were determined. The e ffective dipole moment of the tip is found by a calibration experiment assuming a magnetic dipole-dipole interaction between the tip and another magnetic particle.

In dieser Arbeit wurden auf Substratoberflächen adsorbierte Polymermoleküle mit Rasterkraftmikroskopie (RKM) untersucht. Dabei war die Form der Moleküle (Konformation) von besonderem Interesse. Sie ist von zentralerer Bedeutung in der Polymerphysik und wird üblicherweise in Lösung und mit Streumethoden untersucht. Polymerkonformationen auf Oberflächen sind heutzutage noch wenig untersucht. Üblicherweise wird das Verhalten nach dem so genannten Wormlike-Chain Modell angenommen. Es basiert auf der Annahme, dass die Kettenbiegung nur aus thermischen Fluktuationen resultiert, so dass sich die Kettenform durch statistische Mechanik beschreiben lässt. Es wurden für verschiedene Modellsystem einzelne Moleküle hochaufgelöst abgebildet und die Konformation aus den Bildern bestimmt. Es hat sich gezeigt, dass die idealisierte Vorstellung des Wormlike-Chain Modells tatsächlich nur für wenige der untersuchten Systeme erfüllt ist. Abweichende Konformationen sind oft auffallend regelmäßig: entweder sinusartig mäandrierte oder spiralförmig gedrehte. Beide Charakteristika lassen sich aus dem Prozess der Adsorption erklären, was zeigt, dass die Moleküle auf dem Substrat immobil sind, so dass eine thermische Relaxation der Konformation verhindert ist. Konformtionen lassen sich mit RKM nicht nur beobachten, sondern auch gezielt verändern (Nanomanipulation). Für dendronisierte Polymere konnte so gezeigt werden, dass es einen glasartigen Zustand für das einzelne Molekül gibt. In diesem Zustand verhält sich das Molekül nicht mehr wie eine bewegliche Kette, sondern formstabil, ähnlich einem makroskopischen festen Körper. / In this work single polymer molecules adsorbed onto substrate surfaces were investigated by scanning force microscopy (SFM). The focus was on the shape (conformation) of the molecules, which is of central importance in polymer physics. It is commonly investigated in solutions and with scattering methods. Conformations on surfaces are only little investigated thus far. Often a behavior according to the so-called worm-like chain model is assumed. It is based on the assumption that chain bending results entirely from thermal fluctuations so that the overall chain shape can be described by statistical mechanics. For several model systems single molecules were imaged and the conformation was determined from the images. It was found that the idealistic wormlike chain behavior is only valid for a few systems. Deviations are often remarkable regular: either sine-like undulated or spiral wound. Both characteristics can be explained from the process of adsorption, indicating that molecules are immobile on the substrate so that thermal relaxation is inhibited. Conformations can not only be imaged using the SFM, but also changed in a defined way (nanomanipulation). Manipulation experiments with dendronized polymers the existence of a glassy state for the single polymer. In this state the molecule no longer behaves as a flexible chain but remains its shape, similar to a macroscopic solid body.