Pressure sensitive adhesives are a category of adhesives which can be used for both permanent and removable applications. The use of radiation to cure these materials prior to application is becoming more widespread due in part to the recent drive to reduce the release of volatile organic compounds and hazardous air pollutants produced from more traditional solvent or thermal curing methods. For the manufacturer, a greater understanding of how these adhesives cure under near to real life conditions is highly desired. This thesis presents the first use of one-dimensional magnetic resonance imaging to provide information on the molecular mobility as revealed by spin relaxation times as a function of depth in cross-linking acrylic adhesives during photoinitiated curing by ultraviolet light. Imperfect curing in these adhesives may lead to crosslink density inhomogeneities and consequently, to variations in the adhesion and cohesion properties throughout the depth of the adhesive. The GARField magnet developed at the University of Surrey, along with a new high temperature sample mounting probe developed during this work allowed thin film samples to be measured at various temperatures with a spatial resolution better than 16 mum. Two separate components were identified in the exponential decay of the NMR signal from the bulk adhesive. These were attributed to the inter-crosslinked network and to lower molecular weight dangling chain ends. Curing was seen to increase the fraction of the shorter component indicative of an increase in crosslink density. GARField profiles showed that formulations with additional multifunctional acrylates produced the highest cure owing to the increased crosslink density afforded by the multifunctional acrylates. However, the addition of these groups also led to a reduced homogeneity in the depth of cure. The inclusion of further photoinitiating species, sensitive to a wider range of wavelengths was shown to reduce this effect. Measurements at 60°C showed that UV irradiation was more efficient at producing crosslinks at this temperature. However, the contrast between cured and uncured samples on GARField was reduced due to the additional, thermally driven molecular motion. The activation energy for this thermal motion was calculated to be 0.34 +/- 0.04 eV and 0.28 +/- 0.05 eV for the uncured and cured adhesives, respectively. The irradiation regime only became important when small doses separated by more than 20 minutes were used. This regime led to sufficient build up of oxygen in the upper surface of the adhesive to inhibit the curing reaction.

Results of zero-tension fatigue tests are presented for flat sheet unidirectional 0° and angle-plied +/-45° carbon fibre reinforced plastics. Torsional-shear and transverse fatigue tests were made on hoop-wound tubes. These have shown that surface finish has a significant role in determining the fatigue performance of CFRP.A method is presented for assessing the fatigue stress bandwidth in zero-tension fatigue at 0° CFRP. A mechanism of fatigue failure in 0° CFRP is also postulated. Fatigue induced creep effects were observed during shear loadings and these are shown to relate to cracking and crack growth in +/-45° material. A shell theory analysis of tubular CFRP test-pieces was made which demonstrates the suitability of this specimen for 0° longitudinal and 90° hoop-windings. Hoop-wound tubes were used to show that the mutual interactions between shear and transverse elastic properties are not significantly affected by transverse fatigue stresses.

In the present study a relaxation approach to modelling sound propagation in porous media has been developed. A frequency domain model has been formulated and is shown to allow an analytical transformation of the governing equations in the time domain. The model proposed is an extension of an earlier work by Wilson at al. (1997) and is based on the use of two relaxation times. The model presented requires a set of six measurable parameters, e.g. static flow resistivity, porosity, tortuosity, thermal permeability, viscous and thermal characteristic lengths. It will be shown that the model satisfies the physically correct low and high frequency limits evaluated by Johnson et al. (1987) and therefore allows the prediction of a porous material's behaviour in a wide range of frequencies (and pulse durations when used in time domain). It will also be demonstrated that two different model formulations are necessary depending on the material shape factor values and physical reasons for this are identified. The model has been validated by performing laboratory measurements and numerical simulations in both frequency and time domains for a range of granular and fibrous porous materials. The well-known equivalent fluid model by Johnson et al. (1987), Champoux and Allard (1991) and Lafarge et al. (1997) has been formulated analytically in the time domain and its predictions are compared with those of the relaxation model and the data. In the last section of the work a nonlinear model is developed for finite amplitude sound propagation in porous media and validated using laboratory data for acoustic pulses with different durations and amplitudes.

The investigations reported here address the issue of overcoming loss in a typical isotropic metamaterial. The possibility of adding functionality to such materials, through gyrotropic effects, and diffraction management of nonlinear beams, driven by negative phase accumulation, is presented. Loss is overcome by the introduction of gain to the metamaterial. This is achieved on the basis that typical split-ring metaparticles can be suitably enhanced through the addition of carefully selected diodes. The detailed analysis given here deploys a familiar equivalent circuit model and specific current-voltage characteristics. It is emphasised that conditions must be in place to ensure overall stable material behaviour. The methodology uses convective and absolute instability concepts and it is shown that the latter can be so detrimental as to lead to a much reduced frequency window of operation. Another set of investigations emphasises that surface waves provide a path to new science. Consequently the propagation of surface waves along the interface between a metamaterial and a gyrotropic medium is promising for applications. The investigation outcomes of this complicated system need to demonstrate generation properties in real time. Hence, some unique finite-difference time-domain (FDTD) computations have been developed enabling their interesting connection to the Goos- Hanchen shift to be elegantly displayed. Many interesting forms of surface waves are discussed including the simultaneous generation of TE and TM waves propagating in opposite directions. It is well known that in an isotropic metamaterial backward waves can exist so this property is exploited to create a fascinating form of diffraction management. This is investigated both for the bulk and for cavities and the impact of what is defined as nonlinear diffraction is introduced. Finally, some magnetooptics is introduced that adds even more functionality to the generation of cavity solitons.

The dispersability of graphitic carbon black (Monarch 1000) selected as a model for carbon nanotubes has been investigated in aqueous and non aqueous media using rheological, conductivity measurements and atomic force microscopy. The effectiveness of eight dispersants used for water was investigated namely polyethylene oxide polypropylene oxide ABA copolymers (PE/F 103 with 2x16 ethylene oxide units and PE/F 108 with 2x148 ethylene oxide units), Triton X100 and Triton X405 which contains an alkyl (octyl) phenol group with 10 and 40 ethylene oxide groups attached respectively, Lugalvan BNO12 which is a Naphthol Ethoxylate with 12 ethylene oxide units, sodium dodecylsulfate (SDS) an anionic surfactant with a tail of 12 carbon atoms and sulphate group attached to the tail and Sodium dedecylbenzenesulfonate (SDBS) which contains benzene ring in its anchoring group and NPE1800 (nonyl phenyl polypropylene oxide-polyethylene oxide with 27 ethylene oxide units). While for non polar organic solvents three dispersants namely polyhydroxystearic acid (Hypermer LP1), PEG 30-dipolyhydroxystearic acid (Hypermer B246) and polyisobutylene succinimide (OLOA 11000) were used. Hypermer LP1 is homopolymer and Hypermer B246 is polyhydroxystearic acid/polyethylene oxide/polyhydroxystearic acid ABA block copolymer while OLOA 11000 has polar head group (polyamine) attached to a hydrocarbon chain (polyisobutylene). Two non polar organic solvents decalin and xylene were selected. Decalin is aliphatic in nature while xylene is aromatic and it was observed that dispersing carbon black in xylene was relatively easy but there was not much difference in results for either media, which showed that the role of aromaticity of medium in dispersing graphitic carbon black is not significant. Adsorption isotherms of all dispersants were studied. The adsorption isotherms of PE/F 103 in comparison with PE/F 108 and Triton X100 in comparison with Triton X405 revealed that in molar terms the adsorption decreases with increasing number of ethylene oxide units indicating that adsorption is governed by the size of PEO (polyethylene oxide) chain length. Triton X100, Triton X405, Lugalvan BNO12 and NPE 1800 contain aromatic rings in their anchor group and adsorbed more strongly and proved to be much more efficient stabilizers. SDBS also showed higher adsorption than SDS due to п-п interaction with the graphitic carbon black. In non aqueous media, adsorption is a minimum in molar terms for homopolymer Hypermer LP1 as compared to other polymers. As the whole polymer molecule has affinity to adsorb onto the surface and by consequence the whole molecule may lay flat onto the surface giving smaller adsorption amounts. While Hypermer B246 and OLOA 11000 both dispersants consist of an anchoring group which strongly adsorbs on the surface and stabilising chain which has good solubility in the solvent and extends sufficiently in the solvent to import stability. The relative viscosity-effective volume fraction curves were compared with the theoretical curves for the hard sphere dispersions calculated using Krieger-Dougherty equation and showed that Triton X100, Triton X405, Lugalvan BNO12, NPE 1800, SDS and SDBS dispersions could be prepared at much higher solid fraction than those dispersions stabilized by PE/F 103 and PE/F 108. The results indicate that the presence of aromatic groups in the hydrophobic group and sufficient number of ethylene oxide units in adsorbed layer of the surfactants is desirable in producing the stable dispersions for these graphitic carbon black dispersions and would be sensible choices in stabilising carbon nanotubes. In non aqueous media, Hypermer LP1 did not show good agreement with the Krieger-Dougherty equation; the viscosities were all slightly higher than that predicted by that equation. The other two dispersants Hypermer B246 and OLOA 11000 proved to be good stabilizers for crystalline graphitic carbon black as they made dispersions of lower viscosities. That means homopolymer Hypermer LP1 may be more suitable for polar particles but not effective for hydrophobic surfaces. For hydrophobic surfaces a dispersant with block copolymer structure is required rather than homopolymer. Oscillatory shear measurements showed high values of storage and loss modulus at high volume fractions indicating strong repulsive interactions between the carbon black particles. The effectiveness of all dispersants was investigated by measuring the electrical conductivity measurements of carbon black dispersions prepared by using polymers at their optimum concentrations. PE series and Hypermer LP1 produced flocculated dispersions of much higher electrical conductivity as compared to other polymers which might be due to less number of ethylene oxide units in adsorbed layer. The performance of polymers was also measured by atomic force microscopy which is a characterizing technique to evaluate the effectiveness of polymers by measuring the interaction forces (attractive or repulsive forces) between particles in the presence and in the absence of polymers. Spherical glassy carbon black (2-12 micron size) was used to model Monarch 1000 because a larger size carbon black particle was required in AFM and similar results were observed except PE/F 108. PE/F 108 showed repulsive forces on approach and separation which indicated it an effective stabilizer which was a contradiction with rheology and conductivity experiments. However PE/F 103 and Hypermer LP1 showed an attraction on approach and separation.

The present work investigates the material properties of a thermosetting epoxy polymer modified with various reinforcements of micron-sized glass beads and rubber particles, and nano-sized silica particles and carbon nanotubes. The Young’s modulus of the modified epoxies with rigid additives was significantly increased, especially for the nanocomposites containing high contents of nanosilica or nanotubes. The fracture testing showed that the combination of the soft rubber particles and carbon nanotubes provided the best way to improve the toughness and fatigue performance, because a synergistic effect on the fracture behaviour was obtained in the hybrid-modified epoxies. Fractography showed various mechanisms caused by the addition of the toughening particles, and the main toughening mechanisms are dependent on the modifiers used. Nanotubes operated the debonding, pull-out and void growth mechanisms improve the toughness and fatigue performance of their composites. The inclusion of the rigid spherical particles into the epoxy increased the toughness and fatigue performance via mechanisms of shear band yield and plastic void growth. Rubber cavitation was considered to be the main toughening mechanism in the rubber-modified materials. Several dispersion methods were examined for the multi-walled carbon nanotubes, and the best way to get well-dispersed nanotubes without significant damage was identified. The level of the nanotube dispersion was assessed using a greyscale analysis and transmission optical microscopy. Finally, a sonication process using an ultrasonic probe was chosen to prepare the nanotube-modified epoxies. Modelling work was carried out to predict the toughening contribution from the nanosilica and nanotubes. There was a good agreement between the predictions and the experimental results for the toughness. The modified Halpin-Tsai equation was used to calculate the increased modulus caused by the addition of the nanotubes, and the predicted modulus can fit well with the measured values, even at high nanotube contents which resulted in serious agglomeration.

No description available.

Laminated composites are increasingly employed in a variety of industries ranging from Aerospace to Wind Power. The high specific stiffness and strength of these materials renders their wider application advantageous in many fields. However, the broader implementation of such composites is frequently restrained by their poor impact resistance and damage tolerance. Even events as innocuous as a dropped tool can impart significant damage to such materials. Such damage can lead to drops in the strength and stiffness that are unacceptable for many applications, particularly those in Aerospace. 3D woven composites present a possible means of improving the impact resistance and damage tolerance of composite materials. The incorporation of out-of-plane fibres, transversely passing through layers of in-plane fibres, is the means by which this improvement in performance is obtained. This body of work presents an investigation into the behaviour of three dimensionally woven carbon fibre composites. Specifically, the subject composite fabric had an orthogonally woven three dimensional structure. The novelty of these materials is such that knowledge and understanding of their mechanical behaviour is very limited. The purpose of this work was to remedy this through experimental and analytical analysis of these composites. The 3D woven materials were characterized experimentally using a variety of techniques. In addition to evaluating the material experimentally, analytical methods were also used. Current analytical methods were found to be deficient in their incapacity to account for in-plane crimp on a micro scale. As a result a new micro scale approach for predicting the stiffness and strength of these 3D woven materials was developed. The composites used for this thesis were tested using a variety of means. The range of test methodologies used subjected the materials to in-plane, out-of-plane, dynamic and quasi- static loadings. Techniques used included; tension, shear, impact, compression after impact, bolt shear out and bearing pull through. Other means implemented included microscopy, C-scanning and Digital Image Correlation. In addition, conventional composites made from unidirectional pre-pregs or Non-Crimp Fabrics (NCFs) were tested to provide a basis for comparison. Analysis and prediction of the behaviour of conventional laminated composites can be performed using a variety of methods. While the range of methods available is broad, they commonly use individual plies of composite as their fundamental building blocks. This is both convenient analytically and experimentally as the properties of such individual lamina may be found with reasonable ease. However, 3D woven composites are integrated laminates due to the out‐of‐plane fibres they possess. As a result, the accuracy of conventional experimental or analytical methods for evaluating these materials is likely to be poor. In order to gain a better understanding of the behaviour of these 3D woven materials a new micromechanics model was developed. In contrast to other available methods, this micromechanics approach examines the effect of crimp at the fibre level. The method proposed is also distinct in its capability of simultaneously accounting for varying crimp across and along a section of composite.

Dense ceramic oxygen separation membranes can pass oxygen perm-selectively at elevated temperature and have potential for improving the performance and reducing the cost of several industrial processes: such as the conversion of natural gas to syngas, or to separate oxygen from air for oxy-fuel combustion in electricity generation (to reduce NOx emissions and facilitate CO2 sequestration). These pressure-driven solid state membranes are based on fast oxygen-ion conducting ceramics, but also need a compensating flow of electrons. Dual-phase composites are attractive since they provide an extra degree of freedom, compared with single phase membranes, for optimising the overall membrane performance. In this study, composites containing gadolinia doped ceria (CGO, Ce0.9Gd0.1O2- ) and either strontium-doped lanthanum cobaltite (LSC, La0.9Sr0.1CoO3- or La0.6Sr0.4CoO3- ) or silver (Ag) were investigated for possible application as oxygen separation membranes in oxy-fuel combustion system. These should combine the high oxygen ion conductivity of CGO with the high electronic conductivity and fast oxygen surface exchange of LSC or silver. Dense mixed-conducting composite materials of LSC/CGO (prepared by powder mixing and sintering) and Ag/CGO composites (prepared by silver plus copper oxide infiltration method) showed high relative density (above 95%), low background gas leakage and also good electrical conduction. The percolation threshold of the electronic conducting component was determined to be approximately 20 vol.% for both LSC compositions and 14 vol.% for Ag. Isotopic exchange and depth profiling by secondary ion mass spectrometry was used to investigated the oxygen tracer diffusion (D*) and surface exchange coefficient (k*) of the composites. Composites just above the electronic percolation threshold exhibited high solid state oxygen diffusivity, fast surface exchange activity moderate thermal expansion and sufficient mechanical strength thus combining the benefits of their constituent materials. The preliminary work on oxygen permeation measurement showed that the reasonable magnitude of oxygen fluxes is possible to be achieved. This indicates that the composites of LSC/CGO and Ag/CGO are promising for further development as passive oxygen separation membranes.

This Thesis describes a systematic experimental study of the large strain surface mechanical properties of certain semicrystalline polymers, at the nanometre scale. A poly(etheretherketone) (PEEK) was selected as a model semicrystalline polymer for these investigations, as PEEK is currently finding extensive use in high performance composites. The central theme of the Thesis is to elucidate the nano normal indentation response and the scratch deformation mechanisms of semicrystalline polymers. Effective selection and design improvements of materials in surface engineering and tribological applications require knowledge of their near-to-surface mechanical properties. Therefore, this experimental study seeks to elucidate an understanding of the response of semicrystalline polymers in single point contacts. This Thesis approaches the nano surface mechanical property characterisation using indentation and scratching techniques. Indentation is a relatively simple and virtually nondestructive means of assessing mechanical properties of materials by an indenter, inducing a localized deformation into a solid surface. PEEK and other commercially available common polymers were indented and the data were analysed using a contact compliance method in conjunction with an MTS Nano IIs indenter system. The load-displacement curves, the hardness, the elastic modulus, the plasticity index and the creep response data and associated analysis for the PEEK surfaces are presented as a function of the contact displacement. A comparison of the data for the load-displacement curves, the hardness and the elastic modulus for common commercial polymers is described. A study of surface deformations of the PEEK surfaces when it undergoes scratching by means of conical indenters drawn along the surfaces under different contact conditions is also described. The scratch deformations produced considerable loss in optical appeal and surface mechanical properties of polymeric materials. The experimental investigation of the scratch response of the PEEK is focused upon the contact conditions. Scratch deformation maps have been constructed showing the effect of the normal load, the strain (the contact geometry), the strain rate (the scratching velocity), the contact temperature, the state of interfacial lubrication and the crystallinity of the polymer upon the scratching behaviour of the polymeric surface. The extent and the geometric characteristics of the surface damage produced are determined subjectively using scanning electron microscopy (SEM) and optical profilometry techniques. The nano hardness and the elastic modulus results as a function of contact displacement for PEEK composites are also presented. The fibre oriented PEEK composites were scratched using a pendulum sclerometer to analyze the orientation effects on scratch deformations. Finally, nano indentation results for the modified PEEK surfaces under thermal, solvent and mechanical disruptions are reported. The major conclusions of this Thesis are that the nanoindentations into the polymers show a surface hardening response and are dependent upon the contact conditions. The semicrystalline polymers have bimodal nanoindentation characteristics due to presence of the hard crystalline lamella and the soft amorphous phase. The semicrystalline polymers exhibit periodic fluctuations in surface mechanical properties with increasing penetration depth. The scratch deformations of semicrystalline polymers depend upon the contact conditions. A peculiar fibrillation of the polymeric surface was observed when scratched under severe contact conditions (high normal load and sharp conical indenters). The scratch deformations of fibre oriented polymers are highly fibre orientation dependent relative to the scratch direction. Surface plasticisation of amorphous PEEK has been observed in organic solvents mainly in chlorinated solvents. Semicrystalline PEEK was seen to exhibit considerable inert behaviour to common organic solvents but chlorinated organic solvents has caused decrease in surface mechanical properties. A surface hardening of amorphous PEEK has been observed after immersion in water. A qualitative methodology, based on nanoindentation data, to analyze subsurface deformations of polymers resulting from scratch deformations are also presented.