Soft materials have attracted much scientific and technical interest in recent years. In this thesis, attention has been placed on the underpinning relations between molecular structure and properties of one type of soft matter - main chain liquid crystalline elastomers (MCLCEs), which may have application as shape memory or as auxetic materials. In this work, a number of siloxane-based MCLCEs and their linear polymer analogues (MCLCPs) with chemical variations were synthesized and examined. Among these chemical variations, rigid p-phenylene transverse rod and flat-shaped anthraquinone (AQ) mesogenic monomers were specifically incorporated. Thermal and X-ray analysis found a smectic C phase in most of our MCLCEs, which was induced by the strong self-segregation of siloxane spacers, hydrocarbon spacers and mesogenic rods. The smectic C mesophase of the parent LCE was not grossly affected by terphenyl transverse rods. Mechanical studies of MCLCEs indicated the typical three-region stress-strain curve and a polydomain-to-monodomain transition. Strain recovery experiments of MCLCEs showed a significant dependence of strain retentions on the initial strains but not on the chemical variations, such as the crosslinker content and the lateral substituents on mesogenic rods. The MCLCE with p-phenylene transverse rod showed a highly ordered smectic A mesophase at room temperature with high stiffness. Mechanical properties of MCLCEs with AQ monomers exhibit a strong dependence on the specific combination of hydrocarbon spacer and siloxane spacer, which also strongly affect the formation of ð-ð stacking between AQ units. Poisson s ratio measurement over a wide strain range found distinct trends of Poisson s ratio as a function of the crosslinker content as well as terphenyl transverse rod loadings in its parent MCLCEs.

Acryloyloxybenzoic acid (ABA) was prepared by the condensation reaction of acryloyl chloride with p-hydroxybenzoic acid in alkaline medium. The polymerization and grafting of ABA onto Polypropylene were anticipated to occur simultaneously in melt mixing at high temperature. The monomer showed liquid crystalline property. For a better dispersion of ABA in PP before graft copolymerization, a masterbatch of 50-50 (by weight) low density polyethylene + ABA was prepared, which was then used for 5, 10, 15 % ABA + PP mixtures in the Brabender Plasti Corder. Furthermore, these compositions were reprocessed at the same temperature in the molten state. Compression molding was used to prepare films for characterization experiments at 200 &ordm / C under 15000 psi for approximately 3-5 minutes. The graft copolymers were characterized by several techniques / DSC, FTIR, MFI, SEM and mechanical testing. In DSC thermograms the crystallization of PP was seen at approximately 160&ordm / C. An endothermic peak was also assigned to grafted PABA at 280&ordm / C . The incorporation of ABA onto the PP backbone as a graft copolymer (PABA-g-PP) at low percentages results in a possible rearrangement, where tensile strength values increased, while strain decreased. The grafting goes through thermal radicalic mechanism. MFI values were found to increase from 8.7 to 16.35 g/10 min at 10 wt % ABA, then decreased to 10.57 g/10 min at 15 wt % ABA. It is most likely that the presence of PABA produced easy orientational flow up to 10 % of ABA, but at 15 % ABA addition caused a slight decrease in MFI. The tensile test specimens were analyzed by Scanning Electron Microscope. None of the three samples exhibited phase separation. This observation confirms that the graft copolymerization occurrs in a homogenous manner onto PP. The brittle nature of material is observed at all three compositions.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 97-108). Also available in print.

Semi-crystalline polymers have shown increased crystalline order and size when confined in multilayered films by coextrusion1. The resulting large crystals lead to dramatic improvements in gas barrier properties. Ordered polymers whose characteristics are between that of the liquid phase and the crystalline phase are known as liquid crystalline polymers. The highly ordered mesogens in liquid crystalline polymers contribute to their exceptional bulk properties. In this research, side-chain liquid crystalline polymers were confined in multilayered films, made by either multilayer coextrusion or spin coating, with a non-liquid crystalline polymer in an attempt to improve the ordering of the liquid crystalline mesogens. The liquid crystalline behavior and morphology was studied to understand the correlation between the confinement size and the properties of the multilayer films. Commercial main chain liquid crystalline polymers and hydrogen bonded liquid crystalline polymers were also explored in this research for their use in multilayer coextrusion. / text

Polyetheretherketone (PEEK), a polymer with mechanical strength comparable to human bone, is gaining popularity in the orthopedic field because it can potentially relieve the clinical complications, such as stress shielding effect and inevitable implantation failure, which are caused by the mismatch of the mechanical strength between the current metallic implants and the implantation sites. However, it is bio-inert and requires supplementary modification. Plasma immersion ion implantation (PIII) has been well documented that it is a good way to improve the bioactivity of a biomaterial. It is a method that introduces new elements to the biomaterial, generating bio-functional groups on the material surface without altering its mechanical properties. Hence, the aim of this study is to improve the bioactivity of PEEK by modifying its surface chemistry with the use of water (H2O) and ammonia (NH3) plasma immersion ion implantation (PIII) without altering its mechanical properties. After PIII treatment, a series of surface characterization tests that provide information about the surface properties, such as surface energy, roughness, surface chemical composition and crystallinity of PIII-treated PEEK were carried out. Results show that both H2O PIII and NH3 PIII-treated PEEK had significantly higher surface energy and roughness than untreated PEEK. There was also no significant change in the crystallinity of the PIII-treated PEEK, indicating that PIII treatment will not alter the mechanical properties of PEEK. Improvement in wetting properties of PEEK samples suggest the formation of polar functional groups on the PIII-treated PEEK materials, while the increased in surface roughness may be due to the energetic bombardments of plasma ions on the material surface. The in vitro bioactivity of plasma-treated PEEK was investigated and confirmed with hMSC-TERT. Initial cell attachment, cell spreading area, cell proliferation and differentiation were studied. Cell adhesion and cell spreading were enhanced on PIII-treated PEEK, and higher cell viability was observed on PIII-treated PEEK. Moreover, cell proliferation was promoted on early time point and cell differentiation was also enhanced particularly on day 7 by measuring the alkaline phosphatase activity. Therefore, H2O-PIII and NH3-PIII treatments were able to promote the bioactivity of PEEK samples. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

In this study, the thermal and mechanical properties of poly(ethylenetheraphthalate) (PET)-thermotropic liquid crystal polyester (TLCP), mixtures and poly(methyl methacrylate) (PMMA)-TLCP mixtures were studied. The curing of PMMA-TLCP mixtures was done by heat, gamma radiation and microwave. The amount of TLCP in mixtures was % 0.5, 2 and 5 TLCP by weight. TLCP was synthesized by melt-acidolysis system, and PET-TLCP mixtures were prepared by using lab scale batch mixer. PMMA samples were prepared according to denture manufacturer&rsquo / s procedure. The characterization of polymer samples and mixtures were carried by FT-IR, NMR, DSC, DMA, tensile, impact, three point bending tests and light microscopy. The mixing of TLCP with PMMA yielded heterogeneous dispersions. This was observed from light micrographs. The mechanical and rheological properties of all polymers were not positively affected by inclusion of TLCP. It is also worthwhile to note that weakening of PET-TLCP mixtures were due to the thermal degradation as the thermal age of the mixtures is much higher.

Les matériaux polymères sont largement utilisés pour des applications structurelles dans le secteur automobile et leurs comportements complexes nécessitent des modèles précis pour la simulation éléments finis. Les polymères possèdent un comportement dépendant du temps et de la vitesse. La dépendance à la vitesse peut être observée par un accroissement de la rigidité et de la limite élastique en fonction de la vitesse de déformation. Le long temps nécessaire pour retrouver des contraintes nulles après sollicitation du matériau met en évidence la dépendance du temps sur le comportement. De plus, particulièrement pour les polymères chargés, le phénomène de cavitation se traduisant par la création et la croissance de micro-cavités et de microfissures conduit à un changement de volume durant la déformation. Dans ce travail, un modèle de comportement est développé pour un polymère semi-cristallin chargé de talc utilisé dans l’industrie automobile. Un modèle constitutif viscoélastique-viscoplastique non-associatif avec endommagement non-local est proposé dans le but de simuler les phénomènes observés expérimentalement. Dans le modèle développé, une surface de charge non symétrique est utilisée pour prendre en compte la pression hydrostatique. La viscoplasticité non-associative couplée avec l’endommagement conduit aux déformations viscoplastiques non-isochoriques caractérisées expérimentalement. Les paramètres du modèle proviennent d’essais expérimentaux réalisés sous différentes conditions et `a différentes vitesses de déformation. Pour ces essais, plusieurs techniques de mesure, telles que la corrélation d’images et l’extensommetrie optique sont utilisées pour les mesures de champs de déplacements. La bonne corrélation entre les données expérimentales et les simulations numériques mettent en évidence la précision du modèle développé afin de modéliser le comportement des matériaux polymères semi-cristallins. / Polymer materials are widely used for structural applications in the automotive sector and their behaviours are complex and require accurate models for finite element simulations. Polymer materials exhibit rate and time dependent behaviours. The rate dependency can be observed by an increase of the stiffness and the yield stress at increasing strain rate. The long time to recover the zero stress after solicitation of the material highlight the time dependent behaviour. Furthermore, particularly for filled polymers, the cavitation phenomenon cause the creation and growth of micro-voids and microcracks called damage and leads to volume change during the deformation. In this work, a behaviourmodel for mineral filled semi-crystalline polymer used in automotive industry is developed. A constitutive viscoelastic-viscoplastic non-associated model coupled with nonlocal damage is proposed in order to simulate the phenomena observed experimentally. In the constitutive model, a non symmetric yield surface is used to take the hydrostatic pressure into account. The non associated viscoplasticity coupled with damage leads to the non-isochoric viscoplastic deformation characterised experimentally. The material parameters arise from experimental tests carried out under various loadings and strain rates. For these experimental tests, different measurement techniques like Digital Image Correlation and optical extensometry are used for the displacements and the strain field measurements. The good agreement between the experimental data and the numerical simulations highlights the accuracy of the developed model for polymer modelling.

No description available.

No description available.

The commodity plastics industry is dominated by semicrystalline polymers, which generally display high toughness relative to amorphous polymers but typically suffer from low strength and modulus. Researchers have shown that the addition of nanoparticles (NPs) to these semicrystalline matrices can result in materials with enhanced properties relative to the neat systems. The arrangement of these NPs into anisotropic sheet-like structures appears to endow these processed polymer nanocomposites (PNCs) with further improved mechanical properties relative to PNCs where the NP morphology remains well-dispersed. However, there is currently no appropriate methodology in the literature with which to quantitatively correlate the extent of NP organization to the enhancement in mechanical properties. Additionally, isothermal crystallization (the current processing technique of choice for this class of PNCs) results in numerous grain boundaries. While entanglements across grains can limit issues associated with failure, grain boundaries can also be undesirable for the modulus of the material. In this dissertation, we methodically investigate several key topics related to the above. We first present our modifications to the correlation function approach of Strobl and Schneider, which was originally developed to characterize the structural parameters of neat semicrystalline polymers and their blends, that allow us to apply it to isothermally crystallized poly(ethylene oxide) (PEO) PNCs. We select PEO due to the relative ease with which mobile silica NPs can be dispersed within the matrix. Next, we characterize these materials using the generally used large beam size typical of laboratory-scale and synchrotron X-ray scattering instruments. In this study, we show that our adaptations to the correlation function approach allow for the quantitative evaluation of the NP ordering process as a function of isothermal crystallization temperature. The same systems are then characterized with a microfocus synchrotron X-ray scattering beam guided by an autonomous experimentation protocol, which allows for a detailed, granular mapping of the structural parameters of these materials. The much smaller beam reveals spatial morphological heterogeneity in both the neat and PNC systems due to the grain size being on the order of the dimensions of the microbeam as opposed to those of the larger beam. Hence, the combination of the large and microfocus beam provides a comprehensive view of these systems, with varying degrees of granularity. We also find quantitative evidence that demonstrates that NPs organize parallel to the direction of polymer crystal growth, a phenomenon which has previously only been shown in the literature in a qualitative fashion. Having established the physics of the NP ordering process in isothermally crystallized PNC systems, we turn to the zone annealing (ZA) technique as inspiration to approach more uniform, unidirectionally oriented NP morphologies. ZA, which has found extensive use in the production of ultra-pure semiconductors for electronics applications, proceeds by translating a sample at a constant velocity over a well-defined temperature gradient. This directional processing technique has been shown to result in the reduction of grain boundaries when applied to semicrystalline polymers. Since the PNC is a more complicated system than the neat matrix, we first perform studies of zone annealed neat PEO. Our experimental, analytical, and numerical investigations validate a crucial directional crystallization theory proposed by Lovinger and Gryte, who were among the first to apply ZA to semicrystalline polymers; our experimental evidence confirms the existence of a critical ZA velocity (v_crit) below which directional crystallization occurs and above which the process is closer in spirit to isothermal crystallization. Having determined the mechanism driving the ZA of neat PEO, we then turn to the ZA of PEO-based PNCs. Through our studies, we find that it is imperative to minimize or eliminate sample flow during the procedure, as otherwise the NPs order in disparate directions. Our subsequent redesign of the sample preparation protocol, such that the material is pressed between two glass coverslips separated by Teflon spacers, leads to extensive unidirectional organization of NPs that persists throughout the film at slow enough ZA velocities, as evidenced from X-ray scattering experiments. Hence, this dissertation systematically examines questions relevant to understanding how to obtain uniform, unidirectional NP organization in semicrystalline PNCs, with relevance to applications requiring enhanced properties.