This thesis describes investigations into the photophysical properties of luminescent materials and their application in optoelectronic devices such as light emitting diodes and photodetectors. The materials used were all solution processable because of the interest in low cost processing of organics. I have investigated the photophysics of 1,4,5,8,9,12-hexamethyltriphenylene, a triphenylene derivative which has its luminescence enhanced by the addition of methyl groups. These groups change the planar shape of the triphenylene molecule into a twisted one, changing the symmetry of the molecule and increasing its dipole moment in absorption and emission by ~4 fold. This increased its rate of radiative deexcitation by ~20 times. In addition, the twisted shape of the molecule prevents intermolecular interactions and concentration effects from affecting the luminescence. This results in an efficient solid-state photoluminescence quantum yield of 31%. This thesis also includes an investigation into phosphorescent polymer dendrimers, designed to have suitable viscosities in solution for inkjet printed OLED applications. A photophysical study of the intra-chain aggregation effects on the luminescence was undertaken in both homopolymers and copolymers with high energy gap spacer units. Using double dendrons to increase the steric protection of the luminescent cores, the best homopolymers achieved 12.1% external quantum efficiency (39.3 cd/A) at 100 cd/m² brightness and the best co-polymer achieved 14.7% EQE (48.3 cd/A) at 100 cd/m². This compares favourably with 11.8% EQE for the best phosphorescent polymer and 16% for the best solution processed dendrimer OLED previously reported. Finally I have applied a solution processed enhancement layer to silicon photodiodes to enhance their ultraviolet response. Using a blend of materials to give favourable absorption and emission properties, 61% external quantum efficiency was achieved at 200 nm, which is better than the 20-30% typical for vacuum deposited lumogen enhancement layers used commercially.

Šiame baigiamajame magistro darbe nagrinėjama polistireninio putplasčio stiprumo savybės. Teorinėje dalyje pateikta literatūros analizė, bendros žinios apie polistireninį putplastį, gamybos būdai, panaudojimo galimybės. Išnagrinėta trijų didžiausių gamintojų Lietuvoje siūloma produkcija. Apžvelgti reikalavimai pastatų atitvarų šiluminei varžai, išnagrinėta termoizoliacinio sluoksnio storio pokytis nuo TSRS laikų iki dabar. Eksperimentinėje dalyje aprašomos naudotos medžiagos; jų charakteristikos; gniuždomasis stipris; šliejamasis stipris; išnagrinėta skirtingo tankio bandinių mikrostruktūra ir makrostruktūra. Aprašomi rezultatai, naudojant statistinės analizės programą atliekama jų analizė, suformuluojamos išvados. / The present work of Master degree studies analyzes the properties of expanded polystyrene.Theoretical par of this work introduces analysis of references, general information on expanded polystyrene, manner of production and fields of application. The work analyzes production offered by three biggest manufacturers in Lithuania, reviews the requirements applicable to thermal resistance of enclosures of the building, analyses alteration of thickness of a heat insulation layer comparing the situation in Soviet Union time and nowadays. Experimental part describes the used material, their properties, compressive strength, shear strength; analyses microstructure and macrostructure of samples of different density. The work presents the results and analysis of the results by applying software of statistical analysis; formulation of conclusions.

Materials chemistry basically deals with rational design and synthesis of new solids exhibiting various functional properties. A sound knowledge of crystal structures and chemical bonding is needed to understand the properties of materials. Space group, cell parameters and atomic positions provide a basic crystallographic description of the structure. Crystal structure could be described in a detailed way in terms of close packing of anions and occupancy of cations in different coordination sites. The coordination polyhedra and their interconnectivity bring out the interrelationships between different structures and the properties exhibited. Transition metals (TMs) are d-block elements which occupy groups 3-12 in Periodic Table. IUPAC defines a TM as ‘an element whose atoms have partially filled d-shell, or which can give rise to cations with an incomplete d-shell’. The partially filled d-shell in TMs plays an important role in various chemical and physical properties of TMs. Although TM cations can form compounds with different anions, most of the TM containing compounds are metal oxides due to the large free energies for formation of oxides. Binary TM oxides adopt different kinds of structures among which rock salt (e.g. NiO), rutile (e.g. TiO2), and corundum (e.g. Cr2O3) are most common. Ternary TM oxides are also known to form in variety of structures with the perovskite (e.g. BaTiO3), and the spinel (e.g. MgFe2O4) structures being well known. TM oxides exhibit a broad range of electronic and magnetic properties. TM oxides, at one end, display metallic behavior (e.g. ReO3, RuO2, LaNiO3) due to the delocalized electrons and at other end, show insulating behavior (e.g. NiO) due to the localized electrons. In between, TM oxides have semiconducting properties involving either the hopping of carriers (e.g. partially reduced TiO2, Nb2O5, WO3 and so on) or the electron excitation from the valence band to the conduction band (e.g. SnO2). TM oxides are known to have diverse magnetic properties: diamagnetic (e.g. TiO2, ZrO2), paramagnetic (e.g. VO2, NbO2), ferromagnetic (e.g. CrO2, La0.67Ca0.33MnO3), ferrimagnetic (e.g. Fe3O4, MnFe2O4) and antiferromagnetic (e.g. NiO, LaCrO3). TM oxides with partially filled 3d-shell are expected to be ‘metallic’ according to Bloch-Wilson theory, but in practice they are Mott insulators (localized 3d electrons) because of correlation energy (U) involved in the transfer of d-electrons between adjacent sites. Certain TM oxides also show insulator-metal (I-M) transitions induced by change of temperature, pressure or composition. For example, VO2 and Ba2IrO4 are known for their temperature and pressure induced I-M transitions, respectively. La1-xSrxCoO3 becomes metal at a particular Sr concentration being one of the examples for composition-dependent I-M transition. TM oxides are usually synthesized by conventional ceramic method in which stoichiometric mixture of starting materials is reacted at elevated temperatures. Multiple prolonged heating with intermittent grindings in ceramic method generally results in thermodynamically controlled products. The metastable phases which are of interest may not be obtained by ceramic method. Chimie douce/soft chemistry methods are generally adopted to stabilize the metastable phases. The guiding principle behind the chimie douce is to have kinetic control (rather than thermodynamic control) to realize metastable phases. Accordingly, metastable derivatives are obtained by choosing appropriate precursors, or adopting sol-gel and molten flux or ion exchange/intercalation methods. The present thesis is devoted to an investigation of transition metal oxides towards development of functional materials exhibiting visible light absorption/emission and lithium insertion/extraction for cathode materials in lithium ion battery. TM oxides find application as photovoltaic materials, luminescent emission materials, photocatalysts, light absorption/pigment materials and so on, based on their optical properties. Ferroelectric TM oxides with perovskite structure [Green coloured (KNbO3)1-x (BaNi1/2Nb1/2O3-δ)x] are studied currently as photovoltaic materials which show high open circuit voltage (Voc = 3.5 V) despite very low short circuit current (Vsc = 40 nA cm-2). TM oxides are also known to exhibit photoluminescent emission which could be due to the doping activator ions (e.g. MnII doped Zn2GeO4) or TM oxide (e.g. CaWO4) itself being self-activator. While the green and red emissions are common for TM oxides, blue emission is rare (e.g. Ar+ irradiated SrTiO3 is a blue emitter). Coloured TM oxides with band gap in visible region are employed as photocatalysts for solar water splitting (e.g. yellow BiVO4, yellow Ag3PO4, yellow TaON, red Fe2O3) and photo-oxidation of organic pollutants (e.g. TiO2-xNx and CaCu3Ti4O12). The coloured TM oxides also find application as pigments from early times, for example, Egyptian blue (CaCuSi4O10), Han blue (BaCuSi4O10), Han purple (BaCuSi2O6), Malachite green (Cu2CO3(OH)2), Ochre red (Fe2O3) and many others. A list of pigments based on TM oxides is given in Table 1. Pigment materials are applied as colouring materials in inks, dyes, paints, plastics, ceramics glazers, enamels and textiles. Table 1. List of TM oxide based pigments and their colours Pigment colour Compound White Titanium dioxide (TiO2) Black Iron oxide black (Fe3O4) Red Iron oxide red (Fe2O3), Ca1-xLaxTaO2-xN1+x (yellow-red) Orange Iron oxide orange (Fe2O3) Yellow Yellow ochre [FeO(OH)·H2O] Green Malachite green [Cu2CO3(OH)2], Viridian (Cr2O3. 2H2O), Y2BaCuO5 Blue Egyptian blue (CaCuSi4O10),Cobalt aluminate (CoAl2O4), YIn1-xMnxO3 Purple Han purple (BaCuSi2O6) Violet Cobalt phosphate [Co3(PO4)2] Colours of the TM oxides arise from visible light absorption due to the ligand field d-d electronic transitions. Though d-d transitions are parity forbidden, the selection rules get relaxed due to different reasons such as symmetry reduction (due to distortion) and vibronic couplings. The colour of the TM oxides is influenced mainly by two factors (i) oxidation state of TM ion present and (ii) ligand field around the TM ion produced by anion geometry. In order to develop new pigment oxides, our strategy was to choose colourless metal oxides having unusual (five coordinated geometry) or irregular/distorted (distorted octahedral/tetrahedral) coordination geometries around metal ion and produce coloured oxides by substituting 3d-TM ions at the metal ion site. We made a detailed study on the origin of the colour and pigment quality of the resulting coloured oxides. In the present thesis, which has two parts, the first part (Part 1) discusses the development of 3d-TM ion substituted coloured oxides with potential for pigment applications. Chapter 1.1 describes the purple inorganic pigment, YGa1-xMnxO3 (0 < x ≤ 0.10), based on the hexagonal YGaO3. The metastable series of oxides were prepared by a sol-gel technique where the dried gels, obtained from aqueous solutions of metal nitrates-citric acid mixtures, were calcined for a short duration in preheated furnace around 850°C/10 mins. The purple colour of the oxides arises from the specific trigonal bipyramidal ligand field around MnIII that obtains in the YGaO3 host. Other hexagonal RGaO3 hosts for R = Lu, Tm and Ho substituted with MnIII also produce similar purple coloured materials. In Chapter 1.2, we present a study on substitution of 3d-TM ions in LiMgBO3 host [where Mg(II) has a trigonal bipyramidal (TBP) oxygen coordination)]. We find that single-phase materials are formed for LiMg1-xCo(II)xBO3 (0 < x ≤ 1.0), LiMg1-xNi(II)xBO3 (0 < x ≤ 0.1), LiMg1-xCu(II)xBO3 (0 < x ≤ 0.1) and also Li1-xMg1-xFe(III)xBO3 (0 < x ≤ 0.1) of which the Co(II) and Ni(II) derivatives are strongly coloured, purple-blue and beige-red respectively, thus identifying TBP CoO5 and NiO5 as the new chromophores for these colours. Chapter 1.3 describes the synthesis, crystal structures and optical absorption spectra/colours of 3d-TM substituted α-LiZnBO3 derivatives: α-LiZn1-xMIIxBO3 [MII = CoII (0 < x < 0.50), NiII (0 < x ≤ 0.05) and CuII (0 < x 0.10)] and α-Li1+xZn1-2xMIIIxBO3 [MIII = MnIII (0 < x ≤ 0.10) and FeIII (0 < x 0.25)]. The crystal structure of the host α-LiZnBO3, which is both disordered and distorted with respect to Li and Zn occupancies and coordination geometries, is largely retained in the derivatives, giving rise to unique colours [blue for CoII, magenta for NiII and violet for CuII], that could be of significance for the development of new, inexpensive and environmentally-benevolent pigment materials, especially for the blue colour. Accordingly, the work indentifies distorted tetrahedral MO4 (M = Co, Ni, Cu) (together with a long M-O bond that gives a trigonal bipyramidal geometry) structural units as the new chromophores for the blue, magenta and violet colours respectively, in the α-LiZnBO3 host. In Chapter 1.4, we describe the synthesis, crystal structures and optical absorption spectra of 3d-TM substituted spiroffite derivatives, Zn2-xMxTe3O8 (MII = Co, Ni, Cu; 0 < x ≤ 1.0). The oxides are readily synthesized by solid state reaction of stoichiometric mixtures of the constituent binaries at 620°C/12h. Rietveld refinement of the crystal structures from powder XRD data shows that the Zn/MO6 octahedra are strongly distorted, as in the parent Zn2Te3O8 structure, consisting of five relatively short Zn/MII – O bonds (1.898 – 2.236 Å) and one longer Zn/MII– O bond (2.356 – 2.519 Å). We have interpreted the unique colors and the optical absorption/diffuse reflectance spectra of Zn2-xMxTe3O8 in the visible, in terms of the observed/irregular coordination geometry of the Zn/MII – O chromophores. We could not however prepare the fully-substituted M2Te3O8 (MII = Co, Ni, Cu) by the direct solid state reaction method. Density Functional Theory (DFT) modeling of the electronic structure of both the parent and the transition metal substituted derivatives provides new insights into the bonding and the role of transition metals toward the origin of color in these materials. We believe that transition metal substituted spiroffites Zn2-xMxTe3O8 reported here suggest new directions for the development of colored inorganic materials/pigments featuring irregular/distorted oxygen coordination polyhedra around transition metal ions. Red coloured materials are rare in nature. Li2MnO3 is a unique oxide with an unusual red colour imparted by MnIV ions. Chapter 1.5 describes a detailed experimental investigation of Li2MnO3 together with other related MnIV oxides that probes the red colour of Li2MnO3 as well as its photoluminescence. Optical absorption spectra reveal a strong band gap absorption with a sharp edge at ~ 610 nm and a transparent region between ~ 610 and ~ 650 nm that causes the red colour of Li2MnO3 samples. Octahedral MnIV ligand field transitions, corresponding to both MnIV at ideal sites and MnIV displaced to Li sites in the rock salt based layered structure of Li2MnO3, are observed in the excitation spectra of Li2MnO3 samples. Optical excitation at the ligand field transition energies produces tunable emission in the red-yellow-green region, rendering Li2MnO3 a unique MnIV oxide. The honeycomb ordered [LiMn6] units in the structure likely causes both the absorption and photoluminescence properties of Li2MnO3. Lithium containing TM oxides with rock salt related structure are being investigated extensively for application as next generation cathode materials for Lithium ion batteries (LIBs). Recent research is focused on lithium-rich layered oxides (LLOs) which are solid solutions between Li2MO3 (where M = Ti, Mn and Ru) and LiMO2 (where M = Cr, Mn, Fe, Co, Ni). LLOs have excess lithium in the TM layer in addition to lithium in lithium layer of rock salt derived structure. LLOs have gained attention because of their higher discharge capacity in the range of ~ 250 mAhg-1. While most of the LLOs investigated so far contain 3d-TM ions (Mn, Fe, Co, Ni), recently there has been an interest in the study of the role of ruthenium in addition to 3d-TM ions. We have investigated ruthenium containing LLOs with a view to probe (i) the role of ruthenium and (ii) the concentration of excess lithium in the TM layers in producing higher discharge capacities. The results are discussed in the Part 2 of the thesis.Li5NiMnRuO8(Li[Li0.25Ni0.25Mn0.25Ru0.25]O2) form in the Li2RuO3 crystal structure. Electrochemical studies indicate that the Co-containing oxides exhibit a higher initial discharge capacity (for e.g. ~ 180 mAhg-1 for Li4CoRuO6) as well as a higher reversible discharge capacity (~130 mAhg-1 for Li4CoRuO6) compared to the corresponding Ni-analogs. Participation of oxide ions (higher oxidation state of Ru) in the redox process could explain the higher discharge capacity during the first cycle. Reduced capacity (capacity fade) during the subsequent cycles could arise from the oxygen evolution due to the redox process (2O2- → 2O- → O2), which is not reversible. The present work shows that ruthenium incorporation in rock salt layered oxides along with Co/Ni appears to give a beneficial effect in producing a higher discharge capacity. In addition, the compounds crystallizing with the R-3m structure (related to LiCoO2) appear to give a better reversible capacity than the compounds crystallizing in the C2/c structures (Li2TiO3 and Li2RuO3).

Transparent polycrystalline aluminum oxide is a promising optical material, particularly in applications that require ballistic protection. However, the rhombohedral crystal structure of alumina limits its transparency due to birefringent scattering. One method of reducing birefringent scattering is to align the particles along the same crystallographic direction, minimizing the refractive index mismatch. This dissertation explores the use of high aspect-ratio platelet-morphology alumina powder in order to process a crystallographically aligned polycrystalline alumina part, with improved optical properties. The optimal hot-pressing parameters of non-pre-aligned platelet alumina were explored, showing that a low pre-load pressure (0MPa), a high maximum temperature (1800°C), a low maximum pressure (10MPa), and a long isothermal hold time (>5hrs) yields dense, transparent parts. These parameters resulted in samples with a high in-line transmission (>65%) despite a large grain size (>60μm). This is due to a high degree of crystallographic orientation, which minimizes the refractive index mismatch between grains, reducing birefringent scattering. Pre-alignment resulted in a further increase in crystallographic orientation, indicating that the pre-alignment procedure effectively aligns the platelets along the same crystallographic orientation. However, pre-alignment resulted in a minimal improvement in optical properties due to the pre-aligned platelets decreasing the densification. Mechanical properties were characterized, resulting in a flexure stress and Vickers hardness of approximately 175MPa and 17GPa, respectively. These low mechanical properties are due to the large grain size. The Vickers hardness was also characterized along different alignment/hot-pressing directions, showing that the hardness matches that of sapphire along corresponding crystallographic directions. Modifications to the Rayleigh-Gans-Debye model were made, accounting for crystallographic orientation. The modified model more closely matches the experimental optical data, illustrating the importance of accounting for crystallographic alignment. This dissertation emphasizes the importance of characterizing optical losses in transparent ceramics and how they relate to the microstructure, as well as the significance of crystallographic alignment in a birefringent transparent ceramic like alumina.

<p> Optical metamaterials have triggered extensive studies driven by their fascinating electromagnetic properties that are not observed in natural materials. Aside from the extraordinary progress, challenges remain in scalable processing and material performance which limit the adoption of metamaterial towards practical applications. The goal of this dissertation is to design and fabricate nanocomposite thin films by combining nitrides with a tunable secondary phase to realize controllable multi-functionalities towards potential device applications. Transition metal nitrides are selected for this study due to the inherit material durability and low-loss plasmonic properties that offer stable two-phase hybridization for potential high temperature optical applications. Using a pulsed laser deposition technique, the nitride-metal nanocomposites are self-assembled into various geometries including pillar-in-matrix, embedded nanoinclusions or complex multilayers, that possess large surface coverage, high epitaxial quality, and sharp phase boundary. The nanostructures can be further engineered upon precise control of growth parameters. </p><p> This dissertation is composed of a general review of related background and experimental approaches, followed by four chapters of detailed research chapters. The first two research chapters involve hybrid metal (Au, Ag) - titanium nitride (TiN) nanocomposite thin films where the metal phase is self-assembled into sub-20 nm nanopillars and further tailored in terms of packing density and tilting angles. The tuning of plasmonic resonance and dielectric constant have been achieved by changing the concentration of Au nanopillars, or the tuning of optical anisotropy and angular selectivity by changing the tilting angle of Ag nanopillars. Towards applications, the protruded Au nanopillars are demonstrated to be highly functional for chemical bonding detection or surface enhanced sensing, whereas the embedded Ag nanopillars exhibit enhanced thermal and mechanical stabilities that are promising for high temperature plasmonic applications. In the last two chapters, dissimilar materials candidates beyond plasmonics have been incorporated to extend the electromagnetic properties, include coupling metal nanoinclusions into a wide bandgap semiconducting aluminum nitride matrix, as well as inserting a dielectric spacer between the hybrid plasmonic claddings for geometrical tuning and electric field enhancement. As a summary, these studies present approaches in addressing material and fabrication challenges in the field of plasmonic metamaterials from fundamental materials perspective. As demonstrated in the following chapters, these hybrid plasmonic nanocomposites provide multiple advantages towards tunable optical or biomedical sensing, high temperature plasmonics, controllable metadevices or nanophotonic chips.</p><div><br></div>

<p>  </p> <p>Low-dimensional materials (LDMs) are substances that have at least one dimension with thicknesses in the nanometer (nm) scale. They have attracted tremendous research interests in many fields due to their unique properties that are absent in bulk materials. For instance, in quantum optics/photonics, LDMs offer unique advantages for effective light extraction and coupling with photonic/plasmonic structures; in chemistry, the large surface-to-volume ratio of LDMs enables more efficient chemical processes that are useful for numerous applications. In this thesis, several types of LDMs are studied and engineered with the goal to improve their impact in plasmonic and quantum photonic applications. Two-dimensional hexagonal boron nitride (hBN) is receiving increasing attention in quantum optics/photonics as it hosts various types of quantum emitters that are promising for quantum computing, quantum sensing, etc. In the first study, we explore and demonstrate a radiation- and lithography-free route to deterministically create single-photon emitters (SPEs) in hBN by nanoindentation with an atomic force microscopy. The method applies to hBN on flat, chip-compatible silicon-based substrates, and an SPE yield of up to 36% is achieved. This marks an important step toward the deterministic creation and integration of hBN SPEs with photonic and plasmonic devices. In the second study, the recently discovered negatively charged boron vacancy (V_B^-) spin defect in hBN is investigated. V_B^- defects are optically active with spin properties suitable for sensing at extreme scales. To resolve the low brightness issue of V_B^- defects, we couple them with an optimized nano-patch antenna structure and observe emission intensity enhancement that is nearly an order of magnitude higher than previous reports. Our achievements pave the way for the practical integration of V_B^- defects for quantum sensing. Zero-dimensional nanodiamond is another important host material for solid-state SPEs. Specifically, the negatively charged silicon vacancy (SiV) center in nanodiamonds exhibits optical properties that are suitable for quantum information technologies. In the third study, we, for the first time, demonstrate the creation of single SiV centers in nanodiamonds with an average size of ~20 nm using ion implantation. Stable single-photon emission is confirmed at room temperature, with zero-phonon line (ZPL) wavelengths in the range of 730 – 803 nm. This confirms the feasibility of single-photon emitter creation in nanodiamonds with ion implantation, and offers new opportunities to integrate diamond color centers for hybrid quantum photonic systems. Finally, we have also explored using metal-semiconductor hybrid nanoparticles for plasmon-enhanced photocatalysis. A core-shell nanoparticle structure is synthesized, with titanium nitride (TiN) and titanium dioxide (TiO₂) being the core and shell material respectively. It is observed that such core-shell nanoparticles effectively catalyze the generation of single oxygen molecules under 700-nm laser excitation. The main mechanism behind is the hot electron injection from the TiN core to the TiO₂ shell. Considering the chemical inertness and low cost of TiN, TiN@TiO₂ NPs hold great potential as plasmonic photosensitizers for photodynamic therapy and other photocatalytic applications at red-to-near-infrared (NIR) wavelengths.</p>

yes / This paper investigates the effect of cement based grout rheology on the injection process through coarse aggregate for producing preplaced aggregate concrete. Four different sands were used in the grout production at different water-cement ratios and cement-sand ratios. Superplasticiers and pulverised fuel ash were also employed in the grout production. Coarse aggregate of known weight was compacted into 150 mm cubic forms, and then the grout was injected through a plastic pipe under self weight into the stone ‘skeleton’. It has been found that there are threshold values of the rheological parameters beyond which full injection is not possible. In particular, all grout mixes with and without additives and admixtures exhibited the same yield stress threshold value for full injection, whereas the threshold values for other rheological properties including the grout plastic viscosity, flow time and speed were different according to the materials added to the mix.

<p dir="ltr">The primary goal of this work is to gain a fundamental understanding on how growth conditions affect the morphology and crystallography orientation of CeO₂/Au vertically aligned nanocomposite (VAN) thin films. Focus has been placed on how the changes in morphology and crystallography translate to tunable optical properties. The morphological effects have been observed and analyzed via two main approaches: the change in morphology was observed at multiple points along the film thickness, and the morphology at the film/substrate interface has been analyzed with respect to total film thickness. The changes in Au crystallography orientations have been observed by measuring peak shift in XRD patterns and determining the resulting in- and out-of-plane strain. To observe additional effects of this morphology change, optical measurements have been taken for films at the bottom, middle, and top of the thickness range. Strong trends in transmittance, plasmonic absorption peak shifts and hyperbolic permittivity behavior are correlated with the film thickness. This tunability of optical properties likely arises from changes in both Au pillar phase morphology and crystal orientation. These findings demonstrate that changing film thickness may be a desirable method to easily tune the morphology and optical properties of VAN thin films.</p>

This thesis examines the dynamic mechanical properties of natural silk fibres, mainly from silkworm species Bombyx mori (B. mori) and spider species Nephila edulis, using dynamic mechanical thermal analysis, DMTA. The aim is not only to provide novel data on mechanical properties of silk, but also to relate these properties to the structure and morphology of silk. A systematic approach is adopted to evaluate the effect of the three principal factors of stress, temperature and hydration on the properties and structure of silk. The methods developed in this work are then used to examine commercially important aspects of the ‘quality’ of silk. I show that the dynamic storage modulus of silks increases with loading stress in the deformation through yield to failure, whereas the conventional engineering tensile modulus decreases significantly post-yield. Analyses of the effects of temperature and thermal history show a number of important effects: (1) the loss peak at -60 °C is found to be associated the protein-water glass transition; (2) the increase in the dynamic storage modulus of native silks between temperature +25 and 100 °C is due simply to water loss; (3) a number of discrete loss peaks from +150 to +220°C are observed and attributed to the glass transition of different states of disordered structure with different intermolecular hydrogen bonding. Excess environmental humidity results in a lower effective glass transition temperature (Tg) for disordered silk fractions. Also, humidity-dynamic mechanical analysis on Nephila edulis spider dragline silks has shown that the glass transition induces a partial supercontraction, called Tg contraction. This new finding leads to the conclusion of two independent mechanisms for supercontraction in spider dragline silks. Study of three commercial B. mori cocoon silk grades and a variety of processed silks or artificial silks shows that lower grade and poorly processed silks display lower Tg values, and often have a greater loss tangent at Tg due to increased disorder. This suggests that processing contributes significantly to the differences in the structural order among natural or unnatural silks. More importantly, dynamic mechanical thermal analysis is proposed to be a potential tool for quality evaluation and control in silk production and processing. In summary, I demonstrate that DMTA is a valuable analytical tool for understanding the structure and properties of silk, and use a systematic approach to understand quantitatively the important mechanical properties of silk in terms of a generic structural framework in silk proteins.

L'objectif de ce travail est de comprendre comment la forme intrinsèque des fibres individuelles contrôle les propriétés collectives des empilements, en particulier leurs propriétés mécaniques (élasticité) et électriques. Nous nous intéressons à des fibres longues, alignées selon une direction privilégiée et présentent un désordre de forme important. Notre étude est expérimentale et numérique. Nous proposons un modèle à deux dimensions, de champ moyen auto-cohérent, décrivant l'élasticité collective de l'empilement à partir des propriétés individuelles des fibres : leurs distribution de désordre ainsi que leurs module de courbure. Nous obtenons une équation d'état qui décrit avec un bon accord l'élasticité de nos empilements de fibres, sans paramètre ajustable, mais à un facteur multiplicatif près. Nous obtenons des résultats comparables entre les études expérimentale et numérique. / The purpose of this work is to understand how intrinsic shape of individual fibers controls the collective behavior of fiber stacks, in particular the mechanical (elasticity) and electrical properties. We consider long fibers, aligned towards one preferential direction with a significant disorder shape. Our study is experimental and numerical. We propose a two dimensions self consistent mean field model which describes the collective elasticity from the individual properties of fibers : the disorder distribution and the bending modulus. We obtain an equation of state which describes with a good agreement the stacks elasticity, without any fit parameters, however up to a multiplicative constant. We obtain similar results between experimental and numerical studies.