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.

Enhancing the colloidal stability of nanoparticles dispersions, in order to extend the utilization time without any loss of performance, is desired. Prior works have confirmed the electrosteric stabilization of colloidal particles by so-called “amino-quat-primer” polymers, hyperbranched poly(ethylenimine) polymers containing amino groups and quaternized groups. In this work, a systematic investigation on the factors influencing the polymer-particle-interactions was carried out. Hence, aqueous silica-nanoparticle-dispersions were polymer-functionalized; their dispersions stability was studied using turbidity analysis; and the particle surface charge was examined employing electrophoretic measurements. Five key factors influencing the polymer-particle-interaction were defined, including: the polymer-particle-ratio, the degree of polymerization and the degree of functionalization of the polymer, the dispersion pH and the salt concentration. Alternatingly occurring areas of stable, unstable and again stable dispersions with an increasing polymer-particle-ratio occurred due to a charge reversal of bare, negatively charged to polymer-covered, positively charged particles. An additional area of unstable dispersions at very high polymer concentrations was assumed to arise from depletion forces of non-adsorbed free polymer. Stable, positively charged, polymer-covered silica nanoparticles were obtained for optimized conditions regarding the five key factors. After the dispersion stability enhancement, the new amino-functionalized surface could be used for further modifications, e.g. to result in a compatibility with a polymer matrix to fabricate highly functional polymer / inorganic hybrid materials.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20709号 / 工博第4406号 / 新制||工||1685(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 安部 武志, 教授 陰山 洋, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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<p>Medical devices are at risk of biofouling within seconds after implantation, which can lead to thrombus formation and bacterial contamination. These issues can negatively impact the performance and reliability of the device. Poly(vinyl chloride) (PVC) and polyurethane (PU) are popular synthetic polymers used in biomedical applications, but their hydrophobic nature makes them susceptible to biofouling. To improve their biocompatibility, their surfaces must be modified to be antifouling. However, achieving a thoroughly coated surface through homogeneous activation and effective modification with antifouling polymers remains a challenge, despite recent advancements in polymer surface modification. In this dissertation, we modified the surfaces of medical-grade PVC and PU using hydrophilic and biocompatible polymer brushes via wet chemistry approaches in an aqueous medium. Specifically, we activated the PVC surface with amino groups and then modified it with either modified or synthesized hydrophilic polymers end-capped with reactive groups. Additionally, we coupled a functionalized surface initiator to the activated PVC surface to allow the grafting of different hydrophilic polymers via conventional <em>in situ</em> free-radical polymerization. We followed a similar process to activate the PU surface with amino groups and then coupled a co-initiator derivative to allow the grafting of different hydrophilic polymers via conventional <em>in situ</em> free radical polymerization as a redox initiation system. All the modified surfaces of PVC and PU have exhibited a significant increase in wettability, as well as extremely effective antifouling effects against cell and bacterial adhesion. Overall, the findings of this work demonstrate the applicability of wet chemistry surface modification for PVC- or PU-based medical devices and supplies in biofouling-resistant applications. </p>

No description available.

No description available.

Rapid and high-sensitivity detections of biological analytes are critically important to ensure timely diagnosis of disease and effective monitoring of public health. Although various new biosensing platforms have been established as alternatives to conventional laboratory methods, most of these biosensing platforms suffer from insufficient sensitivities that severely limit their wide applications. To improve the detection sensitivities of these biosensors, surface modifications based on poly(amidoamine) (PAMAM) dendrimers and rolling circle amplification (RCA) have been proven to be effective methods. In this thesis, surface modification strategies based on PAMAM dendrimers and RCA have been applied on three biosensing platforms, including enzyme-linked immunosorbent assay (ELISA), localized surface plasmon resonance (LSPR) sensor chip, and affinity membrane, to improve their detection sensitivities. For the ELISA platform, glass-bottom and poly(styrene) 96-well plates are surface modified by dendrimer-aptamer conjugates to improve detection performances of human platelet-derived growth factor-BB using ELISA. The results show that the ELISA performed using the modified 96-well plates presents a much broader linear detection range and a significantly lower limit of detection (LOD) than conventional ELISA plates. For the LSPR platform, the dendrimer and aptamer modification strategy is employed to surface modify LSPR sensor chips for sensitive detection of the SARS-CoV-2 virus, and an RCA-AuNPs complex is developed to amplify the detection signals. The results show that the modified chip can sensitively detect the SARS-CoV-2 virus with a LOD of 148 vp/mL, suggesting that the modified LSPR chip and signal amplification method can be used for early diagnosis of Covid-19. For the affinity membrane platform, nylon membranes with dendrimer and dual-RCA surface modifications are developed to detect Escherichia coli O157:H7 in food samples. The surface-modified membranes significantly reduce the detection time of the target bacteria to two hours instead of several days using traditional bacterial detection methods. In addition, the new membranes achieve higher sample throughputs (around 4-5 mL/s) with a lower LOD (10 cells/ 250 mL) in processing real-world food samples compared to other similar detection platforms. The excellent properties of our surface modification approaches may provide further advantages when employed in other platforms, such as target separation and enrichment, antifouling and antibacterial, and drug delivery applications.

In spite of the stablility (lack of reactivity) of diamond powder, I have developed a method for tethering alkyl chains and polymers to deuterium/hydrogen-terminated diamond. One method is through ether linkages via thermolysis of di-tert-amyl peroxide (DTAP). This reaction with DTAP has also been applied to grow polymers on the diamond surface. The other method is atom transfer radical polymerization (ATRP), which was applied to grow polystyrene at the surface of diamond. Both polystyrene-modified diamond and sulfonated polystyrene-modified diamond can be prepared by either method, and can be used for solid phase extraction. Diamond stationary phases are stable under basic conditions, which is not the case for silica-based stationary phases. Surface characterization was performed by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). While the main focus of my graduate research has been the surface modification of diamond, I also describe other projects on which I have worked. The use of radical-based processes for modifying diamond is related to a different radical-based synthesis of monolayers or polymers I performed by scribing silicon (Siscr). After preparation of homogeneous olefin-terminated monolayers on scribed silicon made from 1,9-decadiene and chemisorption of Grubbs' catalyst, ring-opening metathesis polymerization (ROMP) of norbornene was demonstrated. These surfaces were characterized by XPS and ToF-SIMS. I also investigated the extent of PDMS oligomers transfer onto different surfaces with a wide range of hydrophobicities, using an uninked, unpatterned PDMS stamp. The effect of surface free energy on PDMS transfer in microcontact printing was investigated and the relationship between the amount of PDMS in ToF-SIMS spectra and the surface tensions of initial surfaces was revealed. Therefore, PDMS transfer can be applied as a probe of surface free energies using ToF-SIMS, where PDMS preferentially transfers onto more hydrophilic surface features during stamping, with little transfer onto very hydrophobic surface features. In much of my thesis work, I performed multivariate analysis of my data, especially of my ToF-SIMS data. Such chemometrics methods include principle components analysis (PCA), partial least squares (PLS) cluster analysis, and multivariate curve resolution (MCR). I also applied these tools to analyze electrospray ionization (ESI) mass spectrometry data from a lipidomics study.

In my research, I have performed many characterization and fabrication experiments that are based on tools of analytical chemistry, materials chemistry, and surface science. My research projects are as follows. (1) Fabrication of transparent polymer templates for nanostructured amorphous silicon photovoltaics was done using low-cost nanoimprint lithography of polydimethylsiloxane. This approach provides a test bed for absorption studies in nanostructured film geometries and should result in improved light capturing designs in thin-film solar cells. Nanopatterned polymer films were characterized by scanning electron microscopy and optical measurements. (2) A straightforward method for fabricating freely suspended, thin, carbon nanotube (CNT) membranes infiltrated with polymers was developed. This process is a new approach for making thin, reinforced, smooth films or membranes with high concentrations of CNTs, which may lead to higher performance materials. Characterization of the film and membrane was performed via scanning electron microscopy and atomic force microscopy. (3) Laser activation-modification of semiconductor surfaces (LAMSS) was carried out on silicon with a series of 1-alkenes. A key finding from this study is that the degree of surface functionalization in a LAMSS spot appears to decrease radially from the center of the spot. These laser spots were studied by time of flight secondary ion mass spectrometry (ToF-SIMS), and the resulting spectra were analyzed using a series of chemometrics methods. (4) A large ToF-SIMS data set from multiple coal samples spanning a wide range of coal properties was subjected to a chemometrics analysis. This analysis separates the spectra into clusters that correspond to measurements from classical combustion analyses. Thus ToF-SIMS appears to be a promising technique for analysis of this important fuel. (5) Several experiments on carbon nanotube processing were performed in my research, including carbon nanotube sheet formation, carbon nanotube purification, carbon nanotube dispersion, and carbon nanotube functionalization. X-ray photoelectron spectroscopy was a key characterization tool for many of these experiments.