The morphology and physicochemical properties of bacterial cells at the molecular level influence their adhesion to surfaces and interfaces. In this study, atomic force microscopy (AFM) was used to explore the morphology of soft, living cells in aqueous buffer, to map bacterial surface heterogeneities, to directly correlate the results in the AFM force distance curves to the macroscopic properties of the microbial surfaces, and to model the experimental AFM force curves using classical Derjaguin-Landau-Verweij-Overbeek (DLVO) theory of colloidal stability. The surfaces of two bacterial species exhibiting different macroscopic surface hydrophobicity, measured as the oil/water contact angle (Ө): Acinetobacter venetianus RAG-1 (Ө =56.4°) and Rhodococcus erythropolis 20SE1c (Ө =152.9°) were probed with chemically functionalized AFM tips, terminated in hydrophobic and hydrophilic groups. All force measurements were obtained in contact mode and made on a location of the bacterium selected from the tapping mode image. AFM imaging revealed morphological details of the microbial-surface ultrastructures with about 20 nm resolution. The heterogeneity in surface morphology was directly correlated with differences in adhesion forces as emphasized by retraction force curves and also with the presence of external structures, either pili or capsules, as confirmed by transmission electron microscopy. The AFM retraction force curves for A. venetianus RAG-1 and R. erythropolis 20S-E1-c showed differences in the interactions of the external structures with hydrophilic and hydrophobic tips. A. venetianus RAG-1 exhibited an asymmetrical pattern with multiple adhesion peaks suggesting the existence of biopolymers with different lengths on its surface. R. erythropolis 20S-E1-c showed long-range attraction forces accompanied by single rupture events indicating a more hydrophobic and smoother surface. The magnitude of the adhesion forces was proportional to the water contact angle on the two bacterial lawns. The experimental force curves between the two microbial cells and functionalized AFM probes presented discrepancies when compared to the classical DLVO theory. Therefore, an extended DLVO model incorporating an acid–base component to account for attractive hydrophobic interactions and repulsive hydration effects was used to assess the additional interactions. Extended DLVO predictions agreed well with AFM experimental data for both A. venetianus RAG-1, whose surface consists of an exopolymeric capsule and pili, and R. erythropolis 20S-E1-c, whose surface is covered by mycolic acids as well as an exopolymeric capsule. The extended model for the bacteria-AFM tip interactions was consistent with the effects of acid base and steric forces, in addition to classical DLVO theory. / Chemical Engineering

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For elucidating catalytic processes and enhancing process efficiency, the characterisation of porous catalysts is crucial. While the chemical characterisation of the catalyst surface, e.g. by infrared and X-ray photoelectron spectroscopy, is standard practice, the energetic characterisation of surface sites is often neglected, although all heterogeneously catalyzed reactions take place at the surface. Inverse gas chromatography is a gas phase method to investigate a large number of physico-chemical, morphological and energetical surface properties of particles, granulates or fibers. In this dissertation, silica materials with well-defined surface properties and a large specific surface area (porous glass beads, pyrogenic silica) were investigated. For potential catalytic and sensoric applications, the silica material was additionally grafted with organofunctional silanes. The overall aim of this Thesis was to apply IGC-theories to different silicas before and after surface modification, to examine the potential of this characterisation method. The validity of the results was set against its limitations, to verify the IGC as sensitive method even for small changes of physico-chemical surface properties. It was observed that the physicochemical properties of the surface are predominatly determined by silanol and siloxane groups. In particular the LEWIS-acid silanol groups strongly interact with LEWIS-basic polar probe molecules. This results in high values for free surface energy with a dominant polar component and an overall LEWIS-acidity of the silica. Measurements indicated specific surface areas respectively to the applied probe molecule. In particular 2-propanol showed strong interactions, a very high surface area, but also a heterogenous adsorption behaviour. According to PAPIRERs Patchwork model of condensation approximation, two different states of adsorption were found. With DFT-simulation these were identified as low energetic hydrogen bonds between 2-propanol and siloxan and as high energetic hydrogen bonds between 2-propanol and silanol groups. Nevertheless, all of the IGC findings point to a reduction of the acidity of silica and an increase in hydrophobicity by surface modification due to the loss of silanol groups with the silane grafting. Finally, the IGC can be presented as a many-faceted useful tool for surface characterisation. Its variability and sensitivity expands most other classical methods. Complex surface properties like free surface energies, acid-base functionality, kinetic parameters, specific surface area and surface heterogenity can be determined from single chromatographic peaks with the respective theories. Throughout the investigation, a new non-linear parameter estimation approach was introduced in contrast to the common linear computation models. Therefore, an increasing number of involved probe molecules and also the use of bipolar probes yields in statistical more reliable results.

Complex engineered nanoparticles (CENPs) are being used on various applications. Their properties are different from those of neat nanoparticles. The dissertation explores these differences from four aspects: 1) Modify carbon nanomaterials’ inert surfaces and investigate the effect on thermal and rheological behavior of their dispersions; 2) Generate self-assembly bi-layer structure of oxide nanoparticles via surface modification; 3) Study interaction between lysozyme and different surface-charged ceria nanoparticles; 4) Investigate the biodistribution and transformations of CENPs in biological media. An environment-friendly surface modification was developed to modify surfaces of carbon nanomaterials for increasing their affinity to non-polar fluid. It can offset formation of agglomerates in dispersions. Less agglomerates change thermal conductivity and rheological behavior. One combined model, considering shape factor, was built to fit non-linear enhancement on thermal conductivity with volume fraction of nanoparticles. Constructing bi-layer structure of oxide nanoparticles with different refractive index was crucial for optical thin films. Silanization was used to transform relatively hydrophilic surface of oxide nanoparticles to hydrophobic surface via attaching alkane chains. The self-assembly separation of these nanoparticles can form bi-layer structure in single deposition process since neat nanoparticles keep in hydrophilic monomer while surface-modified nanoparticles settled down. The adsorption behaviors of lysozyme, one protein with net positive charge, on different surface-charged ceria nanoparticles were investigated. The adsorption isotherm curves were fitted with the Toth and Sips equations satisfactorily. The heterogeneity parameters suggest the surface charge predominate adsorption on negatively charged ceria while lateral effect predominate adsorption on positively charged ceria. The local site energy distributions were also estimated. The 26Al-labeled nanoalumina coated by 14C-labeled citrate was synthesized and its dispersion was infused intravenously into rat. The Accelerator Mass Spectrometer (AMS) was used to measure isotopes in dosing material and tissues. The ratio of coating and core in liver was slightly less than dosing material while the ratios in brain and bone are much higher than dosing material. It may suggest that some citrate coating dissociated from nanoalumina’s surface, entered metabolic cycles, and then redistributed to other organs.