<p> Atomic Layer Deposition (ALD) is a an excellent technique for depositing conformal thin films on complex geometries in layer by layer fashion. The mechanisms of depositing TiO₂, platinum, and ethoxysilane molecules were probed with <i>in situ</i> Fourier transform infrared (FTIR) in order to better understand and improve the process. Each of these studies involves TiO₂. </p><p> There are many uses for thin films of titanium dioxide, a semiconductor and high dielectric material. Current Atomic Layer Deposition (ALD) of TiO₂ generally involves water or ozone, which can oxidize and corrode some substrates of interest. Ritala et al. successfully deposited an assortment of metal oxides using no water, but instead, metal alkoxides and metal halides as precursors. Presented is a study of ALD of titanium dioxide using titanium tetrachloride (TiCl₄) and titanium tetraisopropoxide (TTIP). In situ Fourier transform infrared (FTIR) studies revealed that the mechanism for TiO₂ ALD using titanium tetrachloride and titanium tetraisopropoxide changed with temperature. At temperatures between 250 and 300&deg;, the isopropoxide species after TTIP exposures quickly underwent &beta;-hydride elimination to produce TiOH species on the surface. The observation of propene by quadrupole mass spectrometry supported the &beta;-hydride elimination reaction pathway. Deposition was investigated between 150 and 300&deg; on substrates including zirconia, alumina, and silica. Quartz crystal microbalance results and X-ray reflectivity showed that the system grew 0.5&ndash;0.6 &Aring;/cycle at 250&deg; X-Ray photoelectron studies also confirmed TiO₂ film growth. </p><p> In another aspect of ALD use, self-limiting chemistry assisted with terminating a surface with alkoxysilanes. Tire rubber contains additives such as carbon black or silica particles to provide strength. Although in theory Kevlar fibers would provide strength while lowering the density and increasing car fuel efficiency, in practice Kevlar fibers disperse only very poorly in the rubber, leading to inhomogeneity. In order the increase the mixing likelihood between rubber and Kevlar, the reactions of some sulfurous siloxanes were examined on both aluminum oxide and titanium oxide. The titanium oxide adhesion layer allowed the deposition of molecules on the surface that looked promising for improving mixing with rubber and decreasing the weight of tires. </p><p> Atomic layer deposition offers the possibility of more precision in platinum deposition. In a platinum deposition study, the nucleation and growth of non-conformal platinum on TiO₂ and WO_x powder using Pt(hfac)₂ and formalin was examined with in-situ FTIR and transmission electron microscopy (TEM). Interest in substitution of Pt/C as the oxidation reduction reaction catalyst in polymer electrolyte membrane fuel cells (PEMFCs) led to the ALD synthesis of Pt/WO_x and Pt/TiO₂. A nucleation period on the order of 100 cycles was observed, after which, platinum loading and particle size measurably increased with increasing cycle number. The adsorption of the hfac ligand on the metal oxide substrate effectively inhibits nanoparticle coalescence during the growth phase, which led to further investigation of its use as a site-blocking agent. The results showed that Pt particle distance could be increased with the use of hfacH.</p>

The direct catalytic hydrogenation of acrylonitrile-butadiene-rubber in latex form was studied for the development of a simple process for the modification of unsaturated diene-based polymers. Acrylonitrile-butadiene-rubber, known as NBR, is a rubber synthesized from acrylonitrile and butadiene (monomers) via copolymerization. It has been widely utilized as oil resistant rubber components in industry. Selective hydrogenation of the residual carbon-carbon double bonds (C=Cs) in the NBR backbone could improve its physical and chemical properties which greatly extend its range of application and lifetime. However, the current hydrogenation procedure involves a number of cumbersome steps which substantially increase the production cost. Hence, it is worthwhile developing new technology which HNBR could be synthesized in a cheaper and environmentally friendly way. Considerable efforts have been undertaken to realize this goal. Among them, hydrogenation of commercial NBR latex becomes especially attractive and promising. Direct hydrogenation of NBR in the latex not only avoids using large amounts of organic solvent which is required in polymer solution hydrogenation but also produces hydrogenated-NBR (HNBR) in the latex form which can be utilized for painting or coating. It has been reported that the commercial NBR latex could successfully be hydrogenated using RhCl(PPh3)3 with added triphenylphosphine (PPh3). High quality HNBR latex was obtained after the reaction. However, the hydrophobicity of RhCl(PPh3)3 and PPh3 greatly restrict their separation and diffusion in the NBR latex, resulting in a very low activity in the heterogeneous NBR latex system. In order to improve the process of NBR latex hydrogenation using the RhCl(PPh3)3/PPh3 catalytic system, an in-situ hydrogenation process was developed where RhCl(PPh3)3 was directly synthesized from the water-soluble catalyst precursor RhCl3 and PPh3 in the NBR latex. The catalyst precursor RhCl3 is soluble in the aqueous phase of the NBR latex and PPh3 was well dispersed in the aqueous NBR latex after adding small amounts of alcohol. Compared with using pre-made solid catalyst, the in-situ synthesized catalyst in the NBR latex could quickly be transported into the polymer particles and faster hydrogenation reaction was observed. In addition, the influence of various operational conditions on the hydrogenation rate; such as catalyst concentration, latex system composition, reaction temperature and hydrogen pressure have been studied. With the success of NBR latex hydrogenation using RhCl(PPh3)3 catalyst, two water-soluble analogs of RhCl(PPh3)3, RhCl(TPPMS)3 (TPPMS = Monosulfonated Triphenylphosphane) and RhCl(TPPTS)3, (TPPTS = Trisulfonated Triphenylphosphane) were then used for NBR latex hydrogenation. It was found that the difference of their solubility in water greatly affected their activities in NBR latex hydrogenation. Successful hydrogenation was achieved using the RhCl(TPPMS)3 catalyst while only low conversion was observed when using the RhCl(TPPTS)3 catalyst. The catalysts retention in the polymer is also in agreement with the reaction results. High conversion could only be achieved when the catalyst diffused into the polymer particles in the latex. Using the RhCl(TPPMS)3, the reaction could be carried out in a temperature range of 70??C to 120??C. And no co-catalyst ligand (i.e. TPPMS) was required for catalyst diffusion or reaction. In addition, the effects of the particle size of the NBR latex and the molecular weight of NBR (gel fraction) on hydrogenation were also investigated using lab made ???in-house??? NBR latices. It was found that the hydrogenation reaction was much faster with smaller particle size. It was also observed that the gel fraction in the latex particles greatly influenced the mobility of the polymer chains within the particles. In addition to the rhodium based catalysts, ruthenium based catalysts have also been investigated for NBR latex hydrogenation. With the recent findings of the hydrogenation activity of the Grubbs type metathesis catalyst, the hydrogenation of NBR latex was studied first using the second generation of Grubbs catalyst (G2). It was found using the G2 catalyst with small addition of organic solvent such as mono-chlorobenzene (MCB) to dissolve the catalyst resulted in a successful hydrogenation in NBR latex. Meanwhile, the metathesis activity of the G2 catalyst was also measured during the hydrogenation reaction. Comparing with conventional ruthenium catalysts, the multifunctional G2 catalyst benefited the NBR latex hydrogenation process by controlling its molecular weight change. The increase of molecular weight within hydrogenation reaction was partially offset by a synchronous metathesis reaction between NBR and the added of chain transfer agent (CTA). As a result, no visible gel was observed in the final HNBR product. In addition, the kinetic behavior of the hydrogenation was systematically studied with respect to the catalyst concentration, hydrogen pressure as well as NBR concentration. The apparent activation energy over the temperature range of 80-130??C for the hydrogenation of metathesized NBR was also measured. Further experiments showed that the second generation of Hoveyda-Grubbs catalyst (HG2) could be employed for the NBR latex hydrogenation even without adding any organic co-solvent to dissolve the catalyst. Although HG2 catalyst is insoluble in water, it could be well dispersed in aqueous system with the addition of certain surfactants. A fast catalytic hydrogenation (e.g. TOF > 7000 h-1 at 95 mol.% conversion) was achieved and successful hydrogenation was still observed under very low catalyst concentration. Compared with using G2 catalyst, the degree of metathesis reaction under HG2 in this organic solvent free process was very limited. As a result of this research project, different catalysts were successfully developed for hydrogenation of NBR in latex. A significant milestone was achieved in improving polymer hydrogenation technology.

An investigation to study factors controlling the structure and properties of binary- and ternary-phase polypropylene (PP) composites containing ethylene-propylene rubber (EPR) and glass beads has been carried out. The composite structure was evaluated using various techniques including SEM, DSC, XRD and DMA. While the mechanical tests included tensile and impact measurements at ambient temperature, and a fracture toughness test based on the J-integral method carried out at -20 oC. EPR and glass beads were found to influence the structure and properties of polypropylene in different ways. Incorporation of EPR into polypropylene results in an improvement in impact strength and toughness, accompanied by a decrease in tensile strength and modulus. The opposite was found for composites containing glass beads. Polypropylene composites with balanced mechanical properties were achieved by physical blending of this polymer with both EPR and glass beads. The effect of composite structure, composition and processing variables on the properties of the ternary systems were analysed. A study of their morphology has shown that two kinds of phase structure can be formed, either a separate dispersion of the phases, or encapsulation of the filler by rubber. Factors controlling these structures are believed to be due mainly to the surface characteristics of the components. Modification of EPR by maleic-anhydride grafting results in composites with rubber encapsulation of the filler, with FTIR revealing a reaction between these phases. Composites containing unmodified EPR, on the other hand, show separate dispersion of the components. The former composites, with good adhesion at the rubber and filler interface, have noticeably higher impact strength and fracture toughness at and below ambient temperatures, while the latter variant is characterised by higher tensile strength and modulus, accompanied by a lower impact strength. Improvements in impact strength of the composites was also achieved by promoting adhesion between the polymer and filler interface using surfacecoated glass beads, or by increasing the number of rubber particles adhering to the glass bead surfaces using a two-step mixing technique. Results of the present study have thus shown that mechanical properties of ternary phase polypropylene composites can be adjusted, to a certain extent, by controlling their morphologies through the use of suitable functionalised materials and also by using an appropriate compounding methodology.

The chemical and topographical nature of a polymer surface can be changed by non-equilibrium glow discharge treatment. Surface modification of polysulfone and polyethersulfone was examined using a variety of plasma treatments at a fixed power, pressure and treatment time. The modification observed was found to be dependent upon the type of feed gas employed. Tetrafluoromethane plasmas fluorinate polymer surfaces. The influence of polymeric structure on the extent of modification was examined. Phenyl ring containing polymers experienced a greater extent of modification compared to saturated polymers. The extent of modification is dependent upon both the fluorination mechanism and the surface affinity. Plasmas contain a variety of species accompanied by an electromagnetic spectrum. The role of vacuum ultraviolet radiation in a plasma was investigated as a function of feed gas (argon, krypton, xenon and oxygen) on polyethylene and polystyrene, in an oxygen atmosphere. The xenon vacuum ultraviolet treatment gave rise to the greatest oxidation whilst the O(_2) vacuum ultraviolet treatment was found to result in the least oxidation. The activation mechanisms varied with the feed gas chosen for the experiment. Non-equilibrium glow discharge treatment can alter the transport properties of gases permeating through an asymmetric polysulfone membrane. The selectivity and permeability alter as a function of the treatment. The deposition of a methane plasma polymer onto the surface of the membrane resulted in an increase in the gas flux. Similarly CF(_4) plasma treatment also gave rise to an increase in the gas flux. The deposition of a methane plasma polymer followed by a CF(_4) plasma treatment resulted in a decrease in gas flux and a small increase in the oxygen/nitrogen selectivity.

The aim of this work was to characterise the diffusive properties of superabsorbent polymer systems prepared by free radical crosslinking polymerisation of acrylic acid. The polyelectrolyte nature of these hydrogels gives rise to high swelling capacities, and their ability to absorb and retain water is highly dependent on the precise network structure. Modifying the synthesis formulation results in considerable changes to the dynamic and structural properties of these gels, providing the motive for the work presented here. The influence of two factors, namely the extent of monomer neutralisation and the level of crosslinker in the pre-gel solution, were investigated. The dynamic properties of gels were examined using Quasi-Elastic Light Scattering (QELS), from which the cooperative diffusion coefficient and degree of heterogeneity could be determined. The former was found to increase linearly with neutralisation, due to the introduction of electrostatic interactions. The diffusion coefficient initially remained constant with the addition of crosslinker, due to the dominating influence of physical entanglements, but increased above a threshold crosslinking degree, corresponding to a reduction of the network mesh size. The extent of large-scale inhomogeneity increased for higher ionisations, as both the crosslinker solubility and the efficiency of monomer-crosslinker reaction decreased. However, there was a tendency for concentration fluctuations to be minimised for higher neutralisations, making the gel more microscopically homogeneous. Kinetics of swelling experiments were used to investigate gels of varying composition. The macroscopic diffusion coefficient was found to increase rapidly with increasing neutralisation until the monomer was approximately 35% neutralised, beyond which point counterion condensation caused insignificant variation. This trend was also reflected in the equilibrium swelling ratios, and mode of diffusion. For the majority of gels, the diffusion process was characterised as case II transport. Variation of crosslinking degree caused an overall increase in the diffusion coefficient, reflecting the trend observed in the QELS studies. Nuclear Reaction Analysis (NRA) was used to probe the penetration of heavy water into dry network slabs. The concentration-depth profiles revealed a discontinuity in the diffusion coefficient, corresponding to the transition between glassy and rubbery states, for which the diffusivities differed by several orders of magnitude. The kinetics of plasticisation was assumed to be the rate determining factor in the swelling process, on the timescale of the NRA experiments. The diffusion coefficient for the swollen rubbery region, representative of the macroscopic diffusion process, was found to increase linearly with neutralisation, and decrease with crosslinking degree. The latter observation was explained as due to a reduction in the free volume available for solvent diffusion with higher levels of crosslinker.

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The objective of this research programme was to study the influence of filler incorporation on the rheological, mechanical and morphological properties of high density polyethylene. Several compositions of general moulding grade of HDPE filled with increasing concentrations of diatomaceous earth, an amorphous silica-based particulate mineral of high porosity and friable nature, were compounded in a single-screw extruder. Good filler dispersion into the polymer matrix was achieved with complete polymer permeation through the porous structure of the diatomite particles, and with no apparent filler aggregates or voids being observed on fracture surfaces from SEM photomicrographs of the composites. The specific volume of the filled polymer was a simple linear additive function of the specific volumes of the individual components. DSC measurements carried out on the polyethylene in the composite, indicated very minor influence of the filler incorporation on the crystallinity content of polyethylene and, therefore, the diatomite filler was considered as non-active filler for the polyethylene matrix used.

Plastics glazing materials have properties which allow their widespread use in construction, for example as rootlights. However, they are more susceptible than is glass to degradation by weathering, notably the combined effects of ultraviolet light, heat and moisture. Examples of unacceptable durability have been seen in practice, particularly when high operating temperatures occur in sunlight. Artificial weathering tests are used to assess plastics glazing materials in a reasonably short time, two main types being utilised in this study. The applicability of ultra-fast methods of accelerated degradation has been shown to depend on the extent to which the mechanisms of degradation simulate practical weathering, since different procedures were found to promote different mechanisms in the materials tested. Misleading information was obtained when the full spectrum of solar UV and much of the visible was not adequately reproduced in the accelerated tests. In particular an established grade of PVC-U performed unexpectedly poorly under fluorescent lamps. Procedures based on xenon arc sources were found to be the most generally applicable because they better reproduce the full solar spectrum range and, hence, the typical effects observed in plastics materials in practice. Several analytical techniques were used to characterise the virgin polymers and to assess the weathered materials. Two commercial grades of each polymer type (poly[vinylchloride], polycarbonate and poly[methylmethacrylate]) were studied, and measured changes explained in terms of initial polymer properties. Profiling of chemical (e.g. carbonyl index measured by photo-acoustic fourier transform infrared), physical (e.g. molecular weight, surface gloss/roughness), optical (e.g. colour, light transmission) and mechanical properties (e.g. impact resistance) as a function of exposure period and environmental conditions enabled degradation rates and mechanisms to be established for each material. In conducting these tests particular attention was given to the control and effects of sample temperature during weathering, and to the wavelength range of the light source used. Poly(vinylchloride) was affected much more by weathering at higher temperatures, and by exposure to short wavelength radiation, than was polycarbonate, with acrylic being the most durable overall. Practical applications of this work are through Standards committees primarily. in particular with plastics rootlights (B/542/8 and CEN/TCI28/SC9).