Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: In this thesis the formation and properties of a polymer gel on and at a surface are investigated. The gel under investigation is defined as a three-dimensional network of macromolecules that form permanent links with one another and also with confining planar surfaces. The precise location of the crosslinks on the wall or on another macromolecule is not known prior to linking, and will differ from sample to sample. However, once the crosslinks are formed, they are assumed to be permanent. This random linking is the source of the disorder in the system, over which a quenched average has to be taken. An existing model [9] of network formation, with polymer-polymer crosslinks, is extended to incorporate a surface and polymersurface crosslinks. Within the framework of replica theory, statistical averages and physical properties of the system are calculated by means of a variational approach. Macroscopic information, in terms of the free energy of deformation, is obtained by using two different potentials to simulate the erosslinks mathematically. / AFRIKAANSE OPSOMMING: In hierdie tesis word die vorming en eienskappe van 'n polimeergel, wat teen 'n oppervlak gevorm word, ondersoek. Die gel word gedefinieer as 'n drie-dimensionele netwerk van makromolekules wat permanente bindings met mekaar, maar ook met twee inperkende, platvlakke, vorm. Die presiese ligging van die bindings op die muur en op ander makromolekules is nie vooraf bekend nie, en sal verskil van een gel-monster tot die volgende. Sodra die konneksies egter gevorm is, word aanvaar dat hulle permanent is. Die lukrake bindingsproses is die oorsprong van wanorde in die sisteem, waaroor 'n wanorde-gemiddelde bereken moet word. 'n Bestaande model [9]van netwerkvorming, met polimeer-polimeer bindings, word uitgebrei om 'n oppervlakte en polimeer-oppervlak bindings in te sluit. Statistiese fisika gemiddeldes en fisiese eienskappe van die sisteem word binne die raamwerk van replika-teorie en 'n variasie benadering bereken. Makroskopiese inligting, in terme van die vrye energie van vervorming, word verkry deur twee verskillende potensiale te gebruik om die konneksies wiskundig voor te stel.

No description available.

Several phenyl alkyl bonded phases for liquid chromatography were synthesized and characterized by liquid chromatography, gas chromatography and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The chromatographic physical parameters investigated include a quantitative determination of the mobile phase volume and the stationary phase volume. The stationary phase volume was determined to be a function of the bonded moiety chain length and the chromatographic solvent system employed. The interpretation of the stationary phase volume is discussed in terms of the porous nature of the silica gel support. The chemical parameters determined include a quantitative determination of the mobile phase and stationary phase composition (which were different from each other). The selectivity of the chromatographic separations was dependent on the chemical composition and the volume of both the stationary and mobile phases. Carbon 13 NMR spectroscopy provided information about the environment of the bonded moiety in the stationary phase. The liquid-like nature of the bonded moiety was influenced by the chain length of the attached species, the choice of organic modifier, and the chemical composition of the solvents. Temperature did not appear to play a role in the line widths under the experimental conditions examined. The separation of several peptide diastereoisomers on different commercially available hydrocarbon bonded adsorbents is also reported. Select diastereoisomers of arginine vasopressin and oxytocin are extremely sensitive to differences in the composition of the stationary phase. The selectivity and elution order were dependent upon the choice of adsorbent and solvent system employed. The addition of a second organic modifier provided a method for the dynamic modification of the stationary phase. The ability to dynamically modify the stationary phase can enhance the selectivity for the separation of selected peptide diastereoisomers.

When solutions of various metal 8-quinolinolates or beta-diketonates in an organic solvent were contacted with an aqueous phase and vigorously stirred to generate a large interfacial area, a reversible decrease in the organic phase concentration of the complex was observed. The magnitude of this decrease varied with interfacial area, solvent, temperature, and the nature and concentration of the complex. Analysis of the phenomenon using the Langmuir isotherm showed that the concentration change may be explained by adsorption of significant quantities of the complexes at the increased liquid-liquid interface generated by stirring. Such adsorption was found to complicate extraction kinetics measurements using the high-speed stirring technique when the product chelate is interfacially active, distorting the absorbance/time profile from which rate constants are derived, altering the interfacial area in the reaction vessel, and displacing reactant molecules from the interface. Neutral surfactants were observed to have similar effects. Chelate adsorption was also demonstrated to affect metal ion extraction equilibria, shifting the pH 1/2 value associated with a given metal ion. The magnitude of this shift was found to depend on the concentration of the chelate, its interfacial adsorption constant, and interfacial area. Differences in the pH 1/2 shift were shown to serve as a means of separating metal ions. Studies of the rate of nickel extraction by 8-quinolinols showed that the distribution constant and interfacial activity of the ligand are important factors governing the balance between bulk and interfacial pathways in the extraction. The interfacial rate constant for a given ligand was independent of organic solvent and was typically 10 times larger than the corresponding bulk value, indicating that the interface, although essentially aqueous in character, is a more conducive medium for the reaction of the metal ion and ligand.

Surface enhanced Raman scattering (SERS) is a powerful means for obtaining vibrational data from the metal/electrolyte or metal/gas interfacial environment. However, SERS is only observed for a limited number of metal surfaces under certain experimental conditions. Before this method can become a universal tool, the enhancement mechanism(s) must be understood. The results reported in this dissertation assess both electronic and chemical contributions to the SERS mechanism. The electronic properties of the metal are altered by systematic deposition of Pb or Cu onto a substrate that supports intense SERS, Ag. The chemical nature of the interface is altered with different probe molecules. The effect of Pb deposition on the SERS enhancing ability of Ag electrodes has previously been investigated with strongly adsorbed probe molecules. The behavior of cyanide species in the presence of Pb⁺² is complicated by the necessity of maintaining low solution pH to prevent Pb(OH)₂ precipitation; thus, the predominant solution species is HCN. Although previous reports state that no SERS can be detected from cyanide-containing solutions below pH 6, intense SERS signals can be obtained at pH 2 if sufficiently positive electrode potentials are maintained. The two unresolved SERS bands observed in acidic solutions are attributed to HCN which interacts with the Ag surface in end-on and side-on configurations. The predominant effect of Pb deposition on HCN SERS is HCN displacement. Enhancement due to charge transfer processes is not significant, while electromagnetic effects dictate the residual SERS intensity remaining after the initial HCN displacement. The supporting electrolyte anion affects the rate of change of the potential dependent C≡N stretch in basic CN⁻ media. A correlation between the rate of frequency change and anion charge/radius ratio was observed at potentials near and slightly negative of the Ag potential of zero charge in basic CN⁻ media. These results demonstrate the extraordinary sensitivity of SERS to interfacial conditions. The contributions from chemical and electromagnetic enhancement are further assessed by following excitation wavelength dependence of the SERS intensity of pyridine and Cl⁻ as a function of Cu coverage. Contributions from both are observed, but chemical enhancement is less evident for Cu than for Pb deposition. This is related to the smaller change in work function that occurs as a consequence of Cu versus Pb deposition on Ag surfaces.

A new theory has been proposed for stationary phase formation of chemically modified chromatographic adsorbents. This theory consists of a model in which the bonded hydrocarbon moiety, silica substrate, and their respective solvation layers all participate in stationary phase formation. Stationary phase formation was found to be dependent on three parameters: (1) Solvent strength of the mobile phase components for the bonded organic moiety and the silica substrate; (2) the type of organic moiety covalently bound to the surface; and (3) the bound moiety density or surface coverage. Binary aqueous-organic mobile phases were investigated for LiChrosorb RP-8 and RP-18. For RP-8 the solica substrate played a more important role in stationary phase formation. Whereas, for RP-18 the longer bound hydrocarbon chain dominated stationary phase formation. With different organic modifiers in the mobile phase, the modifier with the larger solvent strength for the bound hydrocarbon was selectively enriched in the stationary phase solvation layer for RP-18. Ternary mobile phase systems were also investigated for RP-18. The second modifier was found to exert a large influence on stationary phase formation. Temperature's role in stationary phase formation was studied with a ternary mobile phase of 40/45/15 methanol, water, THF with RP-18. In this specific case, changing the temperature of the system did not impact on stationary phase formation. A new type of column structure was investigated. This structure involved a totally porous silica gel as compared to a column packed with totally porous silica microparticles. These silica gel columns were characterized both thermodynamically and kinectically. Under Normal Phase chromatographic conditions the silica gel column was found to have a higher selectivity but poorer efficiency for the separation of aniline from nitrobenzene than a packed column. The silica gel can be chemically modified by silane reaction and its bonded phase characteristics were investigated. The gel also showed ion-exchange properties which were investigated using sodium nitrite.

There is an increasing necessity for the pharmaceutical industry to develop enantiomerically pure drugs. Up till now, production of enantiomerically pure molecules has been provided by harvesting them from plants or utilising homogeneous catalysis and biocatalysis. None of these methods are efficient means of production, and attention is now being directed towards heterogeneous enantioselective catalysis as the preferred technique. This is on account of the high product yield and ease of separation of catalyst from the reaction mixture. Over the past few decades, a great deal of research has been conducted into investigating the Ni catalysed hydrogenation of β-ketoesters and Pt catalysed hydrogenation of α-ketoesters. These are the most successful systems for enantioselective heterogeneous catalysis. However, they are unsuitable for industrial purposes due to the low thermal and mechanical stability of the modified surfaces. The main goal throughout this project has been the investigation of surface-confined covalent reactions. The motivation of this research is to develop enantioselective heterogeneous catalysis; covalent networks are believed to infer the necessary thermal and chemical stability required to chirally modify catalytic surfaces for docking interactions with reactant species. Covalent organic frameworks (COFs) on surfaces hold potential for a number of chemical applications, and not just in the field of heterogeneous catalysis; for example in areas such as molecular electronics and templating.

In this thesis, we investigate theoretically a new model of charge regulation of a single charged planar surface immersed in an aqueous electrolyte solution. Assuming that the adsorbed ions are mobile in the charged plane, we formulate a field theory of charge regulation where the numbers of adsorbed ions can be determined consistently by equating the chemical potentials of the adsorbed ions to that of the ions in the bulk. We analyze the mean-field treatment of the model for electrolyte of arbitrary valences, and then beyond, where correlation effects are systematically taken into account in a loop expansion. In particular, we compute exactly various one-loop quantities, including electrostatic potentials, ion distributions, and chemical potentials, not only for symmetric (1, 1) electrolyte but also for asymmetric (2, 1) electrolyte, and make use of these quantities to address charge regulation at the one-loop level. We find that correlation effects give rise to various phase transitions in the adsorption of ions, and present phase diagrams for (1, 1) and (2, 1) electrolytes, whose distinct behaviors suggest that charge regulation, at the one-loop level, is no longer universal but depends crucially on the valency of the ions. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

The growth and morphology of fibroblasts cultured on a physically and chemically modified surface was investigated. The need to understand cellular relationships with surface topography and chemistry is essential in the fields of biomedical engineering and biotechnology. It is well documented that mammalian cell behavior senses and responds to the surrounding micro- and nano- scale environment, but the research defining the chemistry, surface architecture, and material properties for control of this behavior is still in its infancy. The cell response to a substrate is complex, involving membrane proteins, extracellular matrix (ECM), cytoskeletal rearrangement, and changes in gene expression. Conventional cell culture is carried out on two-dimensional (2-D) cell culture platforms, such as polystyrene (PS) or glass, and forces cell behavior to adapt and adhere to an unnatural, planar environment. The biological behavior of these cells is used as a starting point for drug screening, implant design, and metabolic processes, but this is a misrepresentation of cells in their native environment. This discrepancy may be hampering biological research or initiating experimental efforts that are invalid. This body of work seeks to address these issues and contains established protocols for inexpensive, pseudo three-dimensional (3-D) culture scaffolds. The research described offers a multi-disciplinary approach for fabrication of biomaterials to achieve user defined or in vivo cell behavior using human fibroblasts. To provide insight into the design of alternative cell culture templates we have analyzed cell-surface interactions and characterized the surface properties. The substrates fabricated utilized micro-roughened surface topography with 2 – 6 µm wide features and surface chemistry as a method for controlling cell behavior. Surface roughness was templated onto polydimethylsiloxane (PDMS) and PS. The fabricated polymer surfaces have been characterized by atomic force microscopy (AFM), contact angle goniometry, fluorescence microscopy, and infrared (IR) spectroscopy. Initial studies of the textured surface yielded a super-hydrophobic surface with a 154° contact angle and high surface adhesion that was investigated using surface free energy calculations. This was followed by modification of the micro-roughness with self-assembled monolayers (SAMs), proteins, or thin films of polymer for use as a culture platform for cells. Cell behavior on the modified polymers was compared and analyzed against unmodified surfaces and tissue culture PS dishes. Cell morphology on rough PDMS surface was altered by the surface topography decreasing the average cell area to 1760 µm2 compared to an average cell area of 3410 µm2 on smooth PDMS. Gene expression changes were also noted with a 2.3 fold increase in the matrix metalloproteinase, MMP14, in cells on the rough surface compared to cells cultured on Petri dishes. Surface roughness was also combined with other surface modification methods for cell culture, including cell alignment and cell sheet engineering. 50 µm wide lines of fibronectin (FN) patterned on the rough PDMS induced cell directionality while still maintaining a pseudo 3-D culture system creating the first cell culture surface of its kind. The micro-roughness was also templated onto PS and chemically modified with a thermo-responsive polymer. This novel surface produced confluent cell sheets that detached from the surface when cooled below 32°C. Cell sheets cultured on the modified PS surfaces had an increase in FN fibril formation stimulated by the surface roughness when compared to cell sheets detached from a smooth, control surface. The minor alterations to surface topology were proven to be effective in modifying cell biochemical response compared to cells cultured on flat substrates. Differences in surface topography and chemistry stimulated changes in cell adhesion, cytoskeletal arrangement, ECM composition, and gene expression. These cell properties were used as markers for comparison to native cell systems and other reports of 3 D culture scaffolds. The mechanism of altering cell response is discussed in each chapter with respect to the specific type of surface used and compared to cell response and behavior on planar culture systems. New fabrication procedures are described that include the incorporation of other surface modification techniques such as SAMs, surface patterning, and thermo-responsive polymer grafting with surface roughness for original cell culture platforms to mimic an in vivo environment. The research presented here demonstrates that micro- and nano- changes to surface topography have large impacts on the cell-surface relationship which have important implications for research and medical applications involving adherent cells.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Siew-Hoon Lee. / M.S.