The effects of micelle forming surfactants hexadecyltrimethylammonium bromide, sodium dodecyl sulfate and igepal CA~6JO on the visible spectra of merocyanine dyes of the form 1-alkyl-4-[(3', 5'-alkyl oxocyclohexadienylidene)ethylidene]- 1,4-dihydropyridine were studied. In all cases the visible spectrum shifted to the red when the dye was incorporated into the micelles. The magnitude of the shifts was found to be dependent on the substituted groups and the positioning of the chromophore of the dye in the micelle aggregates. The shifts indicate a highly hydrated environment about the surfactant head groups and an environment equivalent to that of pure ethanol solvent at some undetermined penetration distance.

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<p> In this study the experiments were designed to measure the geochemical and surface charge (zeta potential) changes with time for two crushed samples of feldspar (Na-fs and K-fs) over the pH range of most natural waters (5 to 9). These experiments show: </p> <p> (a) the importance of adsorption/desorption phenomena in both short-term and long-term feldspar dissolution, and probably for chemical weathering in general; </p> <p> (b) that the generalized curve which characterizes the geochemical data (an initial rapid rise to a peak followed by a decrease to a lower, either constant or later increasing value) is consistent with a consideration of the adsorption/desorption process (i.e., the formation of the double layer) taking place at the feldspar surface and with the simple dissolution of the mineral; </p> <p> (c) that the cation-silica ratios (Na₂O/SiO₂, K₂O/SiO₂, CaO/SiO₂) of the solution compared to those in the original feldspar indicate an initially incongruent dissolution which tends towards congruency during the latter part of the experiments. </p> <p> From information in the Iiterature and the results of these experiments. it may be concluded that: </p> <p> (a) the most important or master variables in chemical weathering are abrasion, minerologic or crystallographic factors such as twinning, exsolution regions, impurities, fractures and grain size, and solution composition and concentration. pH does not appear to be a master variable in most natural waters, especially for long-term weathering, and the chemical composition of the mineral phase is also not a good criterion for predicting weathering behaviour; and </p> <p> (b) the most extreme chemical weathering should occur in a high energy environment, either for physical reasons (i.e., high abrasion due to extreme relief) or for chemical reasons (i.e., high rainfall). </p> / Thesis / Master of Science (MSc)

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No description available.

The controlled degradation of wood surfaces with infrared light from a CO2 pulsed laser facilitated adhesion without the use of additional resins. Laser modification creates a surface phenomenon that physically and chemically alters the natural biopolymer organization of lignocellulosic materials in a way that promotes adhesion when hot pressed using typical industrial equipment. Laser optimization was determined through mechanical and microscopic observation. It was determined that a mild level of laser surface modification (scale of 30 W/mm2) resulted in the highest bond-line strength. The large spot size of the laser beam resulted in evenly modified surfaces. Surface analysis revealed that laser modification changed native wood morphology, hydrolyzed and vaporized hemicellulose, and enriched the surface with cellulose II and lignin. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR FTIR) was used to analyze the bulk of the laser material. This experiment revealed a change in the hydroxyl region related to hydrogen bonding conformations between wood polymers, mainly cellulose. X-ray photoelectron spectroscopy (XPS) provided an elemental composition of the top 5 nanometers of the surface, which resulted in increased carbon-carbon/carbon-hydrogen linkages and decreased oxygen containing bonds due to laser ablation. Static acid-base contact angle analysis was conducted using three probe liquids to find the Lewis acid, Lewis base, and dispersion components of the top nanometer of surface chemistry. Contact angle analysis revealed laser modified samples had a surface free energy that remained similar to the control wood sample. In addition, the dispersion component of the surface free energy increased due to laser ablation while acid-base components were reduced. Atomic force microscopy (AFM) visually displays a reduction in surface roughness due to the laser technique. An additional set of experiments like thermal gravimetric analysis, thermal pre and post treatments, and heated ATR FTIR and XPS support findings which require more investigation into this adhesion phenomenon. / Master of Science

The critical rupture thicknesses (H_C) of thin liquid films between air bubbles and solid surfaces have been measured using an optical interferometry technique. The results of the measurements show that H_C increases with the increasing hydrophobicity of a solid and varies inversely with the work of adhesion (W_A) of water on the solid. The relationship between H_C and W_A has, therefore, been used to estimate the values of H_C for the systems in which direct measurement is not possible. Thermodynamic calculations have been carried out for the bubble-particle adhesion process using the DLVO theory modified to include interaction energies due to structural forces. The calculations required knowledge of the values of various parameters such as, H_C, zeta potentials, and Hamaker constants for both bubbles and particles. The results of the calculations conducted on methylated silica and coal show that the thin film ruptures mainly due to the attractive structural force (i.e., hydrophobic interaction). For silica and mica immersed in dodecylamine hydrochloride solutions, the major driving force for film rupture is either the attractive electrostatic force or the hydrophobic interaction force, depending on the pH and the amine concentration. / Ph. D.

The effects of gravity on the two-dimensional equilibrium shapes (ES) of crystals and menisci are investigated for different geometries (positions) of the substrate. In the gravity-free case, the equilibrium crystal shape (ECS) is characterized by a scale invariance. The presence of gravity breaks the scale invariance and the resulting ECS changes as the volume of the crystal V is changed. Moreover, the presence of gravity breaks the translational invariance along the direction it acts. Physically realized by the necessity of a support, this is manifested by the existence of an inhomogeneous effective pressure P_eff, which divides the space into two regions, with P_eff either negative or positive. The ECS changes as the crystal passes from one region to another, being concave where P_eff < 0, and convex where P_eff > 0. In all cases it was possible to express the corresponding ECS in terms of the gravity-free one. For the hung crystal, i.e., a crystal pinned to a vertical wall at the top, it is shown that some orientations are missing from the ECS that otherwise will be present in the gravity-free ECS, adsorbed on the same substrate. Thus, facets could disappear from the crystal shape as the volume V or the gravitational acceleration g is increased. A critical volume V_c is found, so that if the crystal volume V exceeds V_c, the crystal cannot be pinned. The ECS can exhibit both concave and convex portions. For a crystal, pinned to a vertical wall at its lower end, we find that it will never develop a concave part. On the other hand, new orientations, absent from the gravity-free crystal, will be present on its ECS. The ES of a free and pinned crystal meniscus is also solved and an expression for the excess (depleted) volume AV is derived. The solution for the crystal meniscus between two walls is also presented. For the pendant crystal, i.e., a crystal hanging from a horizontal support, we find that it can exhibit both concave and convex portions on its ECS. When it develops a concave part, new orientations will appear, compared to the gravity-free case. An intuitive stability criterion is introduced, according to which only crystals wetting the substrate can develop a concave portion before they break. The treatment of a crystal on an inclined substrate shows the complications that arise in determining the ES for a general position of the support as a result of the conflict between the directions associated with gravity and support. An expression for the facet length in the presence of gravity is obtained that is valid for all types of support. For crystal shapes that display a concave portion it offers a very convenient way to experimentally measure step free energies. Thus, by breaking scale invariance, the presence of gravity allows absolute measures of surface energy in contrast to the gravity-free case, where the facet length is proportional to the step free energy by an unknown scale. / Ph. D.

This thesis is concerned with the chemical modification of polymers in the preparation of a library of materials which exhibit altered surface properties as a result of the surface chemical functionality, with particular emphasis on the development of materials that control biofouling and are antibacterial. Chemical modification of crosslinked polystyrene, in film and microsphere form, was carried out by carbene insertion followed by diazonium coupling. This provided access to a collection of materials with varying surface chemistry, whilst the bulk properties of the polystyrene substrates were maintained. Synthesis of the diaryldiazo and the diazonium salts used to perform the surface modifications is described, as well as the preparation and characterisation of the materials. Analysis of the ability of the materials to adsorb and bind the protein bovine serum albumin (BSA) is presented with data obtained from two methods of observation. Quartz Crystal Microbalance with Dissipation (QCM-D) and a protein assay based on the change in optical density of a BSA/PBS solution are used to demonstrate how the specific surface chemistry of the materials influences the ability to adsorb and bind protein. The behaviour of the materials was time dependent and was rationalised with respect to the surface water contact angle and the calculated parameters polar surface area and % polar surface area of the functional groups added to the surfaces. Finally, penicillin loaded materials were prepared and their antibacterial activity was tested against E. coli and S. aureus, demonstrating that the antibiotic is still active from within the polystyrene scaffold.

Fabrication of surfaces with versatile functional groups is an important research area. Hence, it is essential to control and tune the surface properties in a reliable manner. Vinyl-terminated self-assembled monolayers (SAMs) offer significant flexibility for further chemical modification and can serve as a versatile starting point for tailoring of surface properties. Here a synthetic route for the preparation of vinyl-terminated trichlorosilane self-assembling molecules: 9-decenyltrichlorosilane (CH₂=CH-(CH₂)₈-SiCl₃), 10-undecenyltrichlorosilane (CH₂=CH-(CH₂)₉-SiCl₃), and 14-pentadecenyltrichlorosilane (CH₂=CH-(CH₂)₁₃-SiCl₃) is presented. These molecules were used for the preparation of SAMs in either liquid or vapour phase processes. Commercially available methyl-terminated self-assembling molecules: decyltrichlorosilane (CH₃-(CH₂)₉-SiCl₃) and octadecanetrichlorosilane (CH₃-(CH₂)₁₇-SiCl₃) were used as controls. The resultant films were characterised by X-ray photoelectron spectroscopy (XPS), contact angle analysis, ellipsometry, and atomic force microscopy (AFM). Well defined, vinyl-terminated SAMs were further chemically modified with carbenes (:CCl₂, :CBr₂, :CF₂) and hexafluoroacetone azine (HFAA). The reactions were performed in the liquid or the vapour phase. The resulting SAMs were characterised using the same methods as for the vinyl-terminated monolayers. Successful modification was confirmed by the appearance of new signals in the XPS spectrum, with simultaneous changes in water contact angle values and unchanged thickness values. Methyl-terminated SAMs were also exposed to carbenes and HFAA as a control system. These are the first examples of C-C bond formation on SAMs in the vapour phase.