Colombi Ciacchi, Lucio
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Colombi Ciacchi, Lucio
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Colombi Ciacchi, Lucio
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Item-typ:Veröffentlichung, Scanning Kelvin Probe study of electrochemical delamination in adhesively bonded jointsAdhesive bonding is a key technology for the construction of lightweight components and its interest in the industry is increasing due to the several advantages when compared to other joining technologies. A major concern is the long-term stability of adhesive joints, especially for metallic substrates exposed to corrosive media. The aim of this work is to investigate the delamination mechanisms occurring in a real closed adhesive joint geometry. To achieve this purpose, the potential distribution at the metal/polymer interface was measured by means of Scanning Kelvin Probe (SKP) through a thin layer of glass. Quantitative measurements of the delamination kinetics were performed, accompanied by XPS inspection of the fracture surfaces. The delamination rate was found to be hundred times slower than in an open joint geometry. Furthermore, the delamination-limiting step for the open joint is the transport of cations, whereas for the closed joint is limited by the ingress of oxygen along the interphase. The cathodic delamination was the mechanism taking place in both cases, however depending on the geometry of the closed joint also the anodic undermining mechanism was found to occur.Dissertation459 184 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Molecular Dynamics Simulations of the Protein Adsorption Process on OxidesThe adsorption of chymotrypsin and lysozyme on amorphous silica and titania is studied by molecular dynamics (MD) simulations in comparison to experiments. The simulations allow an atomistic view of the adsorption process including long-range interactions, multi-protein effects, contact analysis and surface-induced conformational changes. The surface contact stability is investigated by Steered MD simulations and Atomic Force Spectroscopy experiments. Surface-induced conformational changes are studied by classical and further developed free energy MD methods based on Metadynamics, Replica Exchange Solute Tempering and Umbrella sampling and are compared to circular dichroism experiments. The protein orientation is highly influenced by its dipole moment whereas protein binding motifs are formed mainly by positively charged amino acids. The comparison to the experiment shows that protein-protein interactions and the hydration shell of oxide and protein need to be considered as well.Dissertation375 161 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Molecular Dynamics Simulations of Biological Molecules on the Natively Oxidized Titanium SurfaceIn order to investigate the surface properties of metals in a realistic fashion it is crucial to take into account the thin oxide layer that forms spontaneously when the surface is exposed to an oxidising environment. Starting from reference oxide layer structures obtained in extensive first-principles molecular dynamics simulations, we have developed a novel classical potential which is able to reproduce the topological binding features of the amorphous oxide network on Ti as well as the interfacial behaviour of the TiOx/water interface. By combination of this specific potential with well-established biomolecular force fields, we have performed classical simulations of small organic molecules on the oxide surface and successfully compared their results to DFT calculations. The final model is applied to elucidate the microscopic mechanisms that take place at experimentally relevant bio-interfaces. In particular, we focus on the titanium-binding peptide motif minTBP-1. By using advanced simulation techniques, such as metadynamics, replica exchange molecular dynamics, as well as steered molecular dynamics, we have quantified the adhesion strength to the oxidized titanium surface and to the oxidized silicon surface in excellent agreement with experimental results. A microscopical analysis of the simulations reveals that the stronger adhesion to titanium compared to silicon is primarily caused by differences in the interfacial water structure. Furthermore, we have employed the model to calculate the contact forces between two water-covered titania nanoparticles and compared the results to the findings from AFM experiments.Dissertation333 155 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On the mechanical interactions between TiO2 nanoparticles(2017-03-31); ; ; In this work the mechanical interaction mechanisms between TiO2 nanoparticles at ambient conditions are investigated by using molecular dynamics (MD) and discrete element method (DEM) simulations in comparison to experimental findings. It is shown that the particle interaction forces are crucially determined by the nature of the surface adsorbed water layer of the particles. This dependence controls the characteristic trends of the interparticle forces at the nanoscale with humidity, surface roughness and hydrophilicity. From these insights, comprehensive equations are derived for the calculation of interparticle forces under ambient conditions at the nanoscale. The implementation of these equations into particle contact models enables the fast and accurate simulation of the mechanical behaviour of large nanoparticle assemblies and thus represents a link between the chemical properties of the particle surfaces and the macroscopic mechanical properties of entire nanoparticle films.Dissertation322 186 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Atomistic modeling of the oxidation of titanium nitride and cobalt/chromium alloy surfaces(2009-11-09); ; ; In this work, advanced first-principles molecular dynamics (FPMD) based on density-functional theory are employed to investigate the early oxidation stages of the TiN(110), Co(0001), Cr(110) and CoCr(0001) surfaces. For TiN, I observe selective oxidation of Ti atoms and formation of an ultrathin Ti oxide layer, while Ti vacancies are left behind at the metal/oxide interface. Within the formalism of ab initio thermodynamics I compute the segregation energies of vacancies and vacancy clusters at the metal/oxide interface, comparing the stability of the system obtained by FPMD simulations with ideally reconstructed models. Oxide nucleation on cobalt initially follows a metastable, kinetically driven path that results from the high heat release during the dissociation of O2. The early place-exchange of metal and oxygen atoms leads to the growth of an open, pseudo-amorphous oxide structure with evident Co3O4-like features. Instead, the oxidation of Cr(110) occurs along an energy path close to thermodynamic equilibrium and limited by Cr-ion diffusion already in the earliest oxidation stages. The initial formation of highly oxidized chromate-like structures seems to be precursory for the subsequent growth of Cr2O3 thin films. The oxidation of CoCr alloys occurs via selective oxidation of chromium, which provide vacancies enabling the diffusion of oxygen atoms into inner atomic layers. This outward diffusion of chromium is strongly facilitated by the matrix of amorphous cobalt. In summary, I suggest that superficial oxidation may proceed along two distinct possible pathways: a thermodynamically stable path along the potential energy minimum surface and a metastable, kinetically driven path that results from the high heat release during the dissociation of O2.Dissertation295 163 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Molecular mechanisms of crystal nucleation and growth at ferritin/oxide Interfaces : a theoretical investigation(2018-08-24); ; ; The biomimetic production of micro- and nanostructures from magnetic materials is a suitable way to replace conventional methods with an environmentally friendly and sustainable solution. Biomineralization is nature's way of synthesizing inorganic materials through living organisms. One of the best-known representatives is the protein ferritin, which is found in many organisms and serves as an iron store. Ferritin consists of a total of 24 subunits, which are arranged in the form of a hollow sphere in which iron is biomineralized in the form of iron oxide hydroxide. These subunits were used in this theoretical work and supporting experiments to allow magnetic layers of iron oxide hydroxide to grow without spatial limitations. In this work the different substrate/protein/mineral interfaces, the crystal growth process as well as structure and composition of the resulting mineral phase are analyzed by classical Molecular Dynamic (MD) simulations and quantum mechanical (QM) modelling.Dissertation411 188 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Binding affinities and adhesion phenomena of binding peptides at the interface to zinc oxide(2018-11-20); ; ; Peptide sequences can selectively bind to inorganic substrates in a process similar to the concept of molecular recognition. Here we focused on zinc oxide as an important representative of functional oxides and identified binding peptides with an affinity for different ZnO facets. Five peptides were selected and their conformational ensemble (macrostate) and sensitivity to adsorption were characterised via circular dichroism (CD) spectroscopy. The microstates within their conformational ensembles are accessed by enhanced sampling simulations. To quantify the free energies of adsorption, an optically sectioned indicator displacement assay (O-IDA) was adapted to the peptide/ZnO interface and compared to the results of single molecule force spectroscopy (SMFS), leading to a good agreement between the two approaches.Dissertation393 187 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Experimental Analysis of Interactions between Biomolecules and Inorganic Surfaces(2014-07-01); ; ; Im Rahmen dieser Arbeit wurde die Adsorption von Modellproteinen und -peptiden auf anorganischen Oberflächen (SiO2 und Al2O3) mit Hilfe von Matrix-Assisted Laser Desorption / Ionization Time-of-Flight Mass Spectrometry (MALDI ToF-MS), Atomic Force Microscopy (AFM), Quartz Crystal Microbalance (QCM), Reverse Phase High Performance Liquid Chromatography (RP-HPLC), Protein Assays (BCA Assay) und fluoreszenz-gelabelten Proteinen (FITC-BSA) untersucht. Weiterhin wurde die Immobilisierung von Proteasen (Chymotrypsin) an kolloidalen Partikeln durchgeführt und analysiert.Dissertation302 114 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Biosensing of dissolved analytes with AFM based single molecule force spectroscopy(2016-08-10); ; ; Atomic force microscopy based single molecule force spectroscopy is an important tool for directly investigating the interactions between synthetically engineered biomolecules and different materials interfaces. Based on this technique, biosensors for the detection of adenosine, mercury ions, and thrombin are developed in the thesis. The biosensors based on specific aptamers for the detection of adenosine and mercury ions show extremely high sensitivity and selectivity. A novel method based on single molecule force mapping method is also developed and applied for the detection of mercury ions. The method is simple, quick, and also shows excellent sensitivity and selectivity. In addition, the interactions of avidin biotin and streptavdin biotin are investigated by single molecule force spectroscopy in combination with a specific oligopeptide sequence, with the aim to detecting thrombin in aqueous solution. This system and the underlying sensing principle are relatively complex, so more efforts are needed to improve this biosensora s performance. In summary, it is believed the AFM based single molecule force spectroscopy sensing technique developed in the present thesis will be useful and promising also for many other analytes. It has the potential to be exploited in commercial devices especially because of the low detection limit, if a sufficient degree of automatization and reproducibility are achieved.Dissertation319 120