In an approach to creating molecular-scale structures on glass surfaces via self assembly, a strongly-dimerizing ureido-[2-(4-pyrimidone)] (UPy) quadruple hydrogen-bonding array was chemically immobilized on silica surfaces by way of a triethoxysilane functionality. The unreacted surface silanols were then thoroughly passivated with a monofunctional organosilane, resulting in isolated UPy binding sites on the glass surface. These binding sites were found to selectively bind the strongly fluorescent perylenediimide (PDI) functionalized UPy molecules from solution, thus non-covalently linking the fluorophore to the surface. The association between the self-complementary molecules was exceptionally strong, both in solution and at the surface, such that effective hydrogen-bonding was retained after most solvent treatments. The binding was also reversible, however, so that washes with polar protic and dipolar aprotic solvents with high hydrogen-bonding capabilities, such as water, alcohols, and DMSO, resulted in the removal of the non-covalently bound fluorophore-tagged UPy. The UPy:UPy dimer system was also investigated in solution, using pyrene intramolecular excimer formation as a monitor of the dissociation of the pyrene heterodimers into homodimers incapable of forming excimers at micromolar concentrations. In addition, the energy transfer process in solution between pyrene and perylenediimide fluorophores linked through UPy dimerization was studied, with the intention using FRET-based measurements on the surface at single-molecule levels in order to determine the distances between UPy binding sites. Energy transfer was found to occur, but the observed photophysical behavior was complicated by possible secondary processes, which steady-state fluorescence measurements were unable to elucidate. The benefit of using this UPy system for attaching molecules to a surface lies in its reversibility of binding and versatility in manner of molecules which van be retained on the modified surface with a strong association. In this way molecular-scale features could conceivably be constructed on a surface by self-assembly, with the option of further chemical reactions to lock them in place, thus creating structures beyond the accessibility range of the conventional lithographic methods.

A novel strategy to investigate interfaces relevant to chromatographic separations is presented. The strategy in this dissertation relies on three key ideas: 1) design and fabrication of appropriate model of chromatographic interface, 2) use of forced dewetting to separate interfacial constituent of mobile phase from its bulk component yet preserves the interface, and 3) use of IR spectroscopy and ellipsometry to investigate the structure and thickness of isolated interface.Stratified structures of ultrathin (< 10 nm thick) silica films on gold using gold oxide as adhesive layer and wetting control agent are used as model solid phase. Such design provides chemical environment of bulk silica surface, does not introduce significant spectral background, is suitable for reflection-based spectroscopies, and allow for easy modification to mimic wide range of silica - solvent interfaces. Bare silica-water models capillary electrophoresis interfaces; water-methanol mixture at octadecylsilane-modified silica represents reversed phase liquid chromatography interfaces.Forced dewetting is used to decouple interfacial constituent of mobile phase from its bulk component; yet, the integrity of interface is preserved. This approach, combined with the use of IR spectroscopy and ellipsometry, allowed for ambient atmosphere characterization of these interfacial layers in terms of their structure, composition, and thickness for water at bare silica. Hydrogen bonding was probed in case of complex water-methanol binary mixture at octadecylsilane-modified silica surface.The analysis of residual water layers formed by forced dewetting at bare silica as a function of bulk solution pH shows that the structure of the interfacial layer is highly ordered compared to bulk, and is also pH dependent. Further, thicknesses of interfacial layers were found to be pH dependent and vary from ~6 (pH 1) to ~9 nm (pH 9). Gouy-Chapman-Stern double layer was found to be inadequate to satisfactorily describe observed trends. In addition, surface enhanced infrared absorbance phenomenon was also observed that aided increased quality of resulting IR spectra.The analysis of residual water-methanol layers formed by forced dewetting at octadecylsilane-modified silica surface as a function of gas phase atmosphere shows that the structure of the interfacial layer is highly dependent on the composition of gas phase. The observed changes indicate that condensation of methanol from gas phase into residual layer and/or evaporation of water from residual layer into gas phase may occur in used experimental setup used in this dissertation. For that reason, more precise quantification of relative amounts of water and methanol in residual layers was precluded. Yet, regardless of investigational conditions, two different hydrogen bonding environments for methanol were distinctively observed.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (p. [318]-347).

Deposition of dispersed phase from flowing dispersions onto a substrate surface is of utmost relevance for various industrial processes like fouling of sparingly soluble salts, such as CaCO3 and CaSO4 in heat exchangers and desalination evaporators which tend to form deposits on flow surfaces of tubes or pipelines conveying hard water and in water filtration and purification processes since concentration of CaCO3 in many natural water resources is equal to or greater than the saturation level. The study of deposition is also of intrinsic interest for biophysics and colloid science where vascular calcification i.e. precipitation and deposition of calcium phosphates (hydroxyapatites) in the muscular layer of the blood reduces arterial compliance and promotes congestive heart failure. Experiments were conducted on straight, circular cross section silica tubing of inner di-ameter (ranging from 0.88 mm to3.40 mm) to study the effect of electrostatic interaction and hydrodynamics on the deposition behavior of CaCO3 on silica surface when streams of aqueous solutions of Ca(NO3)2 and Na2CO3 with a concentration of 40.0 g l−1 and 25.9gl−1 respectively flowing at a volumetric flow rate of 1 l h−1 each is mixed to form CaCO3 dispersion which was then transported through silica tubing at a steady volumetric flow rate of 2lh−1. The in situ phenomenology of CaCO3 particles transport, deposition, and evolution of spatial and temporal patterns of the CaCO3 deposition on the silica surface along with the dendritic growth of CaCO3 during the flow was visually documented with the aid of a 100X optical microscope. The study discussed the deposition behavior of dispersed phase of CaCO3 from its aqueous dispersion on the silica tubing during flow and attributed charge inversion from negative to positive of silica surface, due to the adsorption of Na+ formed during precipitation reaction of CaCO3, as a plausible reason for the reversal of electrostatic interaction from attraction between initially negatively charged silica surface and positively charged CaCO3 particles which promoted deposition and subsequent evolution of patterns of CaCO3 deposition on the silica surface during the early stage of experiments to repulsion between finally net positively charged silica surface and positively charged CaCO3 particles which resulted in retarded deposition and subsequent emergence of sparsely adhered CaCO3 agglomerates as localized, limited patches of CaCO3 deposits on the silica surface during the later stage of the experiments

Role of silane-treated stöber silica as reinforcing filler for nitrile rubber (NBR) has been studied. Stöber silica is synthesized by sol–gel method, and the surface of silica is modified with the treatment of silane-coupling agent viz. γ-mercaptopropyltrimethoxysilane (γ-MPS) in varying proportions. Average particle size of stöber silica of spherical shape in the range of 200 to 400 nm is evident from scanning electron microscopy (SEM). Surface modification of silica particle with silane-coupling agents decreases surface energy and reduces agglomeration of silica particles in rubber matrix. Stress–strain study and dynamic mechanical analysis of silica-filled composites are compared with the unfilled ones. Analysis of cross-linking density, mechanical properties, and storage moduli indicates a strong rubber–filler interaction in the silane-treated, silica-filled NBR composites. Silane treatment is found to be effective in uniform dispersion of silica in rubber matrix and in improving the mechanical properties of rubber composite. Different functionalities of organosilane at its both end improve the compatibility of silica with rubber matrix and offer better rubber–filler interaction.

<p>      </p> <p>Full exploitation of shale resources requires new catalytic techniques to efficiently convert the methane, ethane, and propane found in shale gas to value-added fuels and chemicals. A promising process of converting ethane and propane involves catalytic light alkane dehydrogenation and the subsequent oligomerization of light alkenes. The first part of this work focuses on the examination of the mechanistic details of propane dehydrogenation on Pt-based alloy catalysts, where first principles-based free energy, microkinetic, and degrees of rate control analyses are performed to understand and rationalize the selective propane dehydrogenation using a Pt3Mn alloy. We show that only the under-coordinated, Mn-decorated Pt sites, represented by a Pt3Mn(211) surface, are selective to propylene formation, which can be attributed to several key mechanistic details: (1) facile propylene desorption and (2) hindered pathways that are inherently non-selective to propylene and lead to the formation of isomers. These kinetic details can, in turn, be interpreted using the free energy landscapes of propane dehydrogenation on the Pt3Mn(211) surface, which features a reasonably stronger binding of propylene than those of its isomers. From this study, we extract two selectivity descriptors for propane dehydrogenation: The energetics of propylene desorption versus deep-dehydrogenation, as well as the energetics of the formation of propylene versus its isomers. The properties can be used for designing further improved light alkane dehydrogenation catalysts.</p>