Resilin is a disordered elastomeric protein and can be found in specialized regions of insect cuticles. Its protein sequence, functions and dynamic mechanical properties vary substantially across the species. Resilin can operate across the frequency range from 5 Hz for locomotion to 13 kHz for sound production. To understand the functions of different exons of resilin, we synthesize recombinant resilin-like hydrogels from different exons, and investigate the water content and dynamic mechanical properties, along with estimating surface energies relevant for adhesion. The recombinant resilin-like hydrogel has 80wt% water and does not show any sign of tack even though it satisfies the Dahlquist criterion. Finally, doubly shifted dynamic moduli master curves are developed by applying the time-temperature concentration superposition principle (TTCSP), and compared to results obtained with natural resilin from locusts, dragonflies and cockroaches. The resulting master curves show that the synthetic resilin undergoes a prominent transition, though the responsible mechanism is unclear. Possible explanations for the significant increase in modulus include the formation of intramolecular hydrogen bonds, altered structural organization, or passing through a glass transition, all of which have been reported in the literature for polymeric materials. Results show that in nature, resilin operates at a much lower frequency than this glass transition frequency at room temperature. Moreover, recombinant resilins from different clones have comparable resilience with natural resilin, though the modulus is around 1.5 decades lower. Results from the clones with and without chitin binding domains (ChBD) indicate that the transition for the clone without ChBD occurs at lower frequencies than for those with the ChBD, perhaps due to the disordered nature of the clone without ChBD. Atomistic molecular modeling is applied on the repetitive motifs of resilin and different elastomeric proteins to better understand the relationship between elastomeric behavior and amino acid sequences. Results show that the motifs form a favorable bent conformation, likely enabled by glycine's lack of steric hindrance and held in place through intramolecular hydrogen bonds. During Steered Molecular Dynamic (SMD) pulling of these motifs, the hydrogen bonds break and they reform again when the peptides are released to move freely, returning to similar bent conformations. The transition seen in the master curves of recombinant resilins might be due to either these intramolecular hydrogen bonds or to glass transition behavior, though evidence indicates that the transition probably due to the glass transition. What we learned from the synthesized recombinant resilin and simulating the repetitive motifs of resilin may be applicable to the biology and mechanics of other elastomeric biomaterials, and may provide deeper understanding of their unique properties. / Ph. D.

Broadband Dielectric Spectroscopy (BDS) in combination with a nanostructured electrode arrangement – which circumvents the conventional need to evaporate metal electrodes onto soft matter – is used to study the molecular dynamics of several glass forming materials confined in nanometric (> 5 nm) layers. Other complementary experimental tools employed in this work include spectroscopic vis-Ellipsometry (SE), AC-chip calorimetry (ACC), X-ray reflectrometry (XRR), Differential Scanning Calorimetry (DSC) and Atomic Force Microscopy (AFM). The latter is used to characterize the topography of the samples and to determine their thicknesses. Under the conditions of annealing samples (Tg + 50K) in high oil-free vacuum (10E-6 mbars) for at least 12 h and carrying out measurements in inert (dry nitrogen or argon) atmosphere, it is found for all studied thin layers that the structural relaxation, and hence the dynamic glass transition – in its mean relaxation times – remains within a margin ±3 K from the respective bulk behaviour. It is revealed, inter alia, that the one-dimensional confinement of thin films introduces restrictions on other (slower) molecular relaxation processes which manifest, depending on the specific system under investigation, as (i) an interruption of the end-to-end (normal mode) fluctuation of the chains, or (ii) a slowing down of the delta-relaxation when the system is cooled towards glass-formation. Furthermore, (iii) evidence is provided to show that the dimensionality of confinement plays a significant role in determining the resulting dynamics. A molecular understanding of these findings is given, and the discussion presented with respect to the on-going international debate about dynamics in confinement.:1. Introduction 2. The glass transition and chain dynamics 2.1 The phenomenology of the glass transition 2.2 Theories of the glass transition 2.2.1 Free volume theories 2.2.2 Cooperative concepts 2.2.3 Mode-coupling theory 2.3 Dynamics of polymer chains in melt 2.4 The dynamic glass transition in confinement 2.4.1 Experiments: state-of-the-art 2.4.2 Theoretical attempts at explaining dynamics in confinement 3. Sample preparation and experimental techniques 3.1 Thin-film preparation by spin-coating 3.1.1 Films on glass slides 3.1.2 Films on silicon wafers 3.1.3 Reproducibility of sample preparation 3.1.4 Stability of thin film samples 3.1.5 Film thickness determination 3.1.6 Sample annealing experiments 3.2 Use of nanostructured electrodes – a novel approach 3.3 Poly(cis-1,4-isoprene) (PI) in porous media 3.4 Experimental techniques 3.4.1 Broadband Dielectric Spectroscopy (BDS) 3.4.1.1 Polarization 3.4.1.2 Dielectric relaxation 3.4.1.3 Debye relaxation 3.4.1.4 Non-Debye relaxation 3.4.1.5 Dielectric data in the time domain 3.4.1.6 Conductivity contribution 3.4.1.7 The distribution of relaxation times 3.4.1.8 BDS – summary 3.4.2 Spectroscopic Ellipsometry (SE) 3.4.3 AC-chip calorimetry (ACC) 4. Results and Discussion 4.1 Effect of sample geometry on measured dynamics 4.1.1 Introduction 4.1.2 Experimental details 4.1.3 Results and discussion 4.1.4 Summary 4.2 Dynamics of polystyrene in a wide range of molecular weights 4.2.1 Introduction 4.2.2 Experimental details 4.2.3 Results and discussion 4.2.4 Summary 4.3 Molecular dynamics of itraconazole confined in thin supported layers 4.3.1 Introduction 4.3.2 Experimental details 4.3.3 Results and discussion 4.3.4 Summary 4.4 Segmental and chain dynamics in nanometric layers of poly(cis-1,4-isoprene) 4.4.1 Introduction 4.4.2 Experimental details and data analysis 4.4.2.1 Sample preparation 4.4.2.2 Data analysis 4.4.3 Results and discussion 4.4.3.1 1- versus 2-D confinement of poly(cis-1,4-isoprene) 4.4.4 Summary 5 Conclusions 5.1 Dynamics in confinement – a wider perspective

Thermal control in spacecraft will be increasingly important as the spacecraft grows smaller and more compact. Such spacecraft with low thermal mass will have to be designed to retain or reject heat more efficiently. The passive smart radiation device (SRD) is a new type of thermal control material for spacecraft. Current space thermal control systems require heaters with an additional power penalty to maintain spacecraft temperatures during cold swings. Because its emissivity can be changed without electrical instruments or mechanical part, the use of SRD decreases the request of spacecraft power budget. The (SRD) based on VO2 films is one of the most important structures of the functional thermal control surface, being lighter, more advanced and without a moving devices. A large portion of the heat exchange between an object in space and the environment is performed throughout radiation, which is in turn determined by the object surface properties. The modulation device is coated on the spacecraft surface and thus provides a thermal window that can adapt to the changing conditions in orbit. VO2 is well known to have a temperature driven metal to insulator transition ≈ 68ᴼC accompanying a transformation of crystallographic structure, from monoclinic (M-phase, semiconductor) at temperature below 68ᴼC to tetragonal (R-phase, metal) at temperature above 68ᴼC. This transition temperature is accompanied by an increase of infrared reflectivity and a decrease of infrared emissivity with increasing temperature. This flexibility makes VO2 potentially interesting for optical, electrical, and electro-optical switches devices, and as window for energy efficiency buildings applications. This study reports on effect of thickness on VO2 as well as the effect of proton irradiation on VO2 for active smart radiation device (SRD) application. VO2 was deposited on mica by Pulsed laser deposition techniques. The thickness of the film was varied by varying the deposition time. To characterize VO2 the following techniques were performed: XRD, AFM, SEM, TEM, XPS, RBS, RAMAN and transport measurements for optical properties. The effect of proton irradiation was observed using the SEM, where the change in structure, from crystal grains to rods, was observed. / Physics / M.Sc. (Physics)

One of the most important and interesting unsolved problems of science is the nature of glassy dynamics and the glass transition. It is quite an old problem, and starting from the early20th century there have been many efforts towards a sound understanding of the phenomenon. As a result, there are a number of theories in the field, which do not entirely contradict each other, but between which the connection is not entirely clear. In the last couple of decades or so, there has been significant progress and currently we do understand many facets of the problem. But a unified theoretical framework for the varied phenomena associated with glassiness is still lacking. Mode-coupling theory, an extreaordinarily popular approach, came from Götze and co-workers in the early eighties. The theory was originally developed to describe the two¬ step decay of the time-dependent correlation functions in a glassy fluid observed near the glass transition temperature(Tg). The theory went beyond that and made a number of quantitative predictions that can be tested in experiments and simulations. However, one of the drawback of the theory is its prediction of a strong ergodic to non-ergodic transition at a temperature TMCT; no such transition exists in real systems at the temperatures at which MCT predicts it. Consequently, the predictions of the theory like the power-law divergences of the transport quantities (e.g., viscosity and relaxation time) fail at low enough temperature and the theory can not be used below TMCT. It is well understood now that MCT is some sort of a mean-field theory of the real phenomenon, and in real systems the transition predicted by MCT is at best avoided due to finite dimensions and activated processes, neither of which is taken into account in standard MCT. Despite its draw backs, even the most severe critic of the theory will be impressed by its power and the predictions in a regime where it works. Even though the non-ergodic transition predicted by the theory is averted, the MCT mechanism for the increase of viscosity and relaxation time is actually at work in real systems. The status of MCT for glass transition is ,perhaps, similar to the Curie-Weiss theory of magnetic phase transition and it will require hard work and perhaps a conceptual breakthrough to go beyond this mean-field picture. Discussion of such a theoretical framework and its possible directions are, however, beyond the scope of this thesis. In the first part of this work, we have extended the mode coupling theory to three important physical situations: the properties of fluids under strong confinement, a sheared fluid and for the growth kinetics of glassy domains. In the second part, we have studied a different class of non equilibrium phenomenon in arrested systems, the fluctuation relations for yielding. In the first chapter, we talk about some general phenomenology of the glass transition problem and a few important concepts in the field. Then we briefly discuss the physical problems to be addressed in detail later on in the thesis followed by a brief account of some of the important existing theories in the field. This list is by no means exhaustive but is intended to give a general idea of the theoretical status of the problem. We conclude this chapter with a detailed derivation of MCT and its successes and failures. This derivation is supposed to serve as a reference for the details of the calculations in later chapters. The second chapter deals with a simple theory of an important problem of lubrication and dynamics of fluid at nanoscopic scales. When a fluid is confined between two smooth surfaces down to a few molecular layers and an normal force is applied on the upper surface, it is found that one layer of fluid gets squeezed out of the geometry at a time. The theory to explain this phenomenon came from Persson and Tosatti. However, due to a mathematical error, the in-plane viscosity term played no role in the original calculation. We re-do this calculation and show that the theory is actually more powerful than was suggested originally by its proponents. In the third chapter, we work out a detailed theory for the dynamics of fluid under strong planar confinement. This theory is based on mode-coupling theory. The walls in our theory enter in terms of an external potential that impose a static inhomogeneous background density. The interaction of the density fluctuation with this static background density makes the fluid sluggish. The theory explains how the fluid under strong confinement can undergo a glassy transition at a higher temperature or lower density than the corresponding bulk fluid as has been found in experiments and simulations. One of the interesting findings of the theory is the three-step relaxation that has also been found in a variety of other cases. The fourth chapter consists of a mode-coupling calculation of a sheared fluid through the microscopic approach first suggested by Zaccarelli et al[J. Phys.: Condens. Matter 14,2413(2002)]. The various assumptions of the theory are quite clear in this approach. The main aim of this calculation is to understand how FDR enters with in the theory. The only new result is the modified form of Yvon-Born-Green(YBG) equations for a sheared fluid. Then we extend the theory for the case of a confined fluid under steady shear and show that a confined fluid will show shear thinning at a much lower shear rate than the bulk fluid. When a system is quenched past a phase transition point, phase ordering kinetics begins. The properties of the system show “aging” with time, and the characteristic length scale of the quenched system grows as one waits. The analogous question for glasses has also been asked in the contexts of various numerical and experimental works. We formulate a theory in chapter five for rationalizing these findings. We find that MCT, surprisingly, offers an answer to this key question in glass forming liquids. The challenge of this theory is that care must be taken in using some equilibrium relations like the fluctuation-dissipation relation(FDR), which is one of the key steps in most of the derivations of MCT. We find that the qualitative, and some times even the quantitative, picture is in agreement with numerical findings. A similar calculation for the spin-glass case also predicts increase of the correlation volume with the waiting time, but with a smaller exponent than the structural glass case. We extended this theory to the case of shear and find that shear cuts off the growth of the length-scale of glassy correlations when the waiting time becomes of the order of the inverse shear rate. For the case of sheared fluid, if we take the limit of the infinite waiting time, the system will reach a steady state. Then, the resulting theory will describe a fluid in sheared steady state. The advantage of this theory over the existing mode-coupling theories for a sheared fluid is that FDR has not been used in any stage. This is an important development since the sheared steady state is driven away from equilibrium. Interestingly, the theory captures a suitably-defined effective temperature and gives results that are consistent with numerical experiments of steady state fluids(both glass and granular materials). We give the details of a theoretical model for jamming and large deviations in micellar gel in the sixth chapter. This theory is motivated by experiments. Through the main ingredient of the attachment-detachment kinetics and some simple rules for the dynamics, the theory is capable of capturing all the experimental findings. The novel prediction of this work is that in a certain parameter range, the fluctuation relations may be violated although the large deviation function exists. We argue that a wider class of physical systems can be understood in terms of the present theory. In the final chapter, we summarize the problems studied in this thesis and point out some future directions.

No description available.

Thermal control in spacecraft will be increasingly important as the spacecraft grows smaller and more compact. Such spacecraft with low thermal mass will have to be designed to retain or reject heat more efficiently. The passive smart radiation device (SRD) is a new type of thermal control material for spacecraft. Current space thermal control systems require heaters with an additional power penalty to maintain spacecraft temperatures during cold swings. Because its emissivity can be changed without electrical instruments or mechanical part, the use of SRD decreases the request of spacecraft power budget. The (SRD) based on VO2 films is one of the most important structures of the functional thermal control surface, being lighter, more advanced and without a moving devices. A large portion of the heat exchange between an object in space and the environment is performed throughout radiation, which is in turn determined by the object surface properties. The modulation device is coated on the spacecraft surface and thus provides a thermal window that can adapt to the changing conditions in orbit. VO2 is well known to have a temperature driven metal to insulator transition ≈ 68ᴼC accompanying a transformation of crystallographic structure, from monoclinic (M-phase, semiconductor) at temperature below 68ᴼC to tetragonal (R-phase, metal) at temperature above 68ᴼC. This transition temperature is accompanied by an increase of infrared reflectivity and a decrease of infrared emissivity with increasing temperature. This flexibility makes VO2 potentially interesting for optical, electrical, and electro-optical switches devices, and as window for energy efficiency buildings applications. This study reports on effect of thickness on VO2 as well as the effect of proton irradiation on VO2 for active smart radiation device (SRD) application. VO2 was deposited on mica by Pulsed laser deposition techniques. The thickness of the film was varied by varying the deposition time. To characterize VO2 the following techniques were performed: XRD, AFM, SEM, TEM, XPS, RBS, RAMAN and transport measurements for optical properties. The effect of proton irradiation was observed using the SEM, where the change in structure, from crystal grains to rods, was observed. / Physics / M.Sc. (Physics)

La majorité des adhésifs utilisés dans l’industrie marine sont des polymères avec un comportement mécanique qui est fortement influencé par les conditions environnementales (vieillissement hydrique ou température). Par conséquent, il est très important pour les ingénieurs travaillant dans des bureaux d’études d’être capable de prendre en compte ces effets lors des différentes étapes de développement et conception des assemblages collés.Le présent travail propose une méthode d’analyse de l’influence du vieillissement hydrique sur le comportement mécanique d’un adhésif structural époxy dans un assemblage collé. Tout d’abord, un modèle viscoélastique-viscoplastique a été développé pour caractériser la réponse mécanique de l’adhésif dans un joint de colle. Pour cela, le dispositif expérimentalArcan a été utilisé. Le modèle est identifié en utilisant la méthode d’identification inverse et les échantillons sont testés à l’état non-vieilli (pas de vieillissement hydrique). Les résultats obtenus après la démarche d’identification sont utilisés pour prédire le comportement mécanique d’éprouvettes massiques.Dans un deuxième temps, afin de diminuer les temps de saturation d’échantillons, l’évolution des propriétés mécaniques de l’adhésif est analysée sous différentes conditions de vieillissement hydrique (immersion dans l’eau de mer et en humidité relative contrôlée) grâce à des essais sur éprouvettes massiques.Les résultats obtenus seront utilisés pour identifier l’évolution de chaque paramètre du modèle proposé, en fonction de la quantité d’eau absorbée. En parallèle, un modèle de diffusion a été développé pour caractériser le gradient de teneur en eau des joints de colle. Les deux approches sont ensuite combinées pour modéliser les profils d’eau pour différents temps de vieillissement et prédire l’évolution des propriétés mécaniques du joint de colle après le vieillissement. Finalement, pour valider la méthode proposée, la prédiction du modèle est comparée avec des essais réalisés sur assemblages collés vieillis. / Most of the adhesives used in the marine industry are polymers with a mechanical behaviour which is strongly influenced by environmental conditions (water activity or temperature). Therefore, it is important for engineers and designers to be able to consider these effects during the different stages of development and manufacturing of a bonded structure.The present work presents a method for analyzing the influence of water ageing on the behaviour of an epoxy adhesive in an adhesively bonded assembly.First, a viscoelastic-viscoplastic model is developed to characterise the mechanical response of the adhesive at initial state in a bonded joint using the modified Arcan device. The model is identified using the inverse identification method and the considered samples are tested at an unaged stage (no water activity). The results obtained after the identification process are used to predict the bulk behaviour of the adhesive. A comparison between numerical results and experimental tests realised on bulk specimens is then made in order to validate this first approach.In a second phase, in order to decrease the times for samples saturation, the evolution of the mechanical properties of the adhesive in bulk form is tested under different water ageing conditions (immersion in seawater and different relative humidity). The obtained results allowed to identify the evolution of the model parameters as a function of water content. In parallel, a diffusion model was developed to characterise the water ingress in the bonded joint. These two approaches are then combined to model the water profiles and to consider the evolution of mechanical properties of a water aged adhesively bonded assembly, for different immersion times. Finally, to validate the framework, the prediction is compared with experimental tests performed on aged specimens.

<p>Relationships between stresses during the drying process, particle structural and functional properties, and particle engineering by the drying process were addressed in this thesis. In the first part, the importance of the drying phase and the effect of the drying rate on the intragranular porosity of microcrystalline cellulose pellets were investigated. Differences in porosities of dried pellets could be explained by liquid-related differences in densification during convective drying rather than by differences in densification during wet agglomeration. An increased drying rate gave more porous pellets with a lower compression shear strength, and thereby stronger tablets. The next part dealt with modulation of solid-state stability and tabletting behaviour of amorphous lactose by incorporation of different polymers by spray drying. Increased content and molecular weight of poly(vinylpyrrolidone) (PVP) resulted in an increased resistance to crystallisation provoked by heat and moisture. The stabilising effect was even more evident after long-term storage. However, the glass transition temperature was almost unaffected and may, therefore, be questioned as a stability indicator for these types of materials. The presence of the polymers resulted in somewhat less deformable particles. Incorporation of PVP increased the compactability, whilst a surfactant decreased it, which could be shown to be related to differences in particle-particle adhesivity between the different particles. This thesis contributes to increased mechanistic understanding in the area of particle engineering that may lead to better prediction and optimisation of the functionality of pharmaceutical particles, which is of the utmost importance in the development and production of solid dosage forms.</p>

Relationships between stresses during the drying process, particle structural and functional properties, and particle engineering by the drying process were addressed in this thesis. In the first part, the importance of the drying phase and the effect of the drying rate on the intragranular porosity of microcrystalline cellulose pellets were investigated. Differences in porosities of dried pellets could be explained by liquid-related differences in densification during convective drying rather than by differences in densification during wet agglomeration. An increased drying rate gave more porous pellets with a lower compression shear strength, and thereby stronger tablets. The next part dealt with modulation of solid-state stability and tabletting behaviour of amorphous lactose by incorporation of different polymers by spray drying. Increased content and molecular weight of poly(vinylpyrrolidone) (PVP) resulted in an increased resistance to crystallisation provoked by heat and moisture. The stabilising effect was even more evident after long-term storage. However, the glass transition temperature was almost unaffected and may, therefore, be questioned as a stability indicator for these types of materials. The presence of the polymers resulted in somewhat less deformable particles. Incorporation of PVP increased the compactability, whilst a surfactant decreased it, which could be shown to be related to differences in particle-particle adhesivity between the different particles. This thesis contributes to increased mechanistic understanding in the area of particle engineering that may lead to better prediction and optimisation of the functionality of pharmaceutical particles, which is of the utmost importance in the development and production of solid dosage forms.

The hole-doped perovskite manganese oxide such as Ln1-xAxMnO3 (Ln = La, Nd, Pr, and A = Ca, Sr, Ba, Pb) is one of the most studied topics in the recent years due to the observation of colossal magnetoresistance (CMR). Basically, LaMnO3 has an almost insulating behavior and on antiferromagnetic arrangement. By substituting a divalent cation (A2+) in place of La3+, LaMnO3 can be driven into metallic and ferromagnetic state. Mixed valence of Mn 3+ / Mn4+ is needed for both metallic behavior and ferromagnetism in these materials. The CMR characteristic occurs in the ferromagnetic state. A systematic investigation of the structural, magnetic and electrical properties in the perovskite colossal magnetoresistance materials La0.7-xLnxPb0.3Mn1-yMeyO3 (Ln=Pr, Nd and Y, Me=Fe and Co) has presented in this thesis. By subatituting Nd, Pr, Y for the La and Co, Fe for the Mn, the substitution effects on the crystallographic deformation, magnetotransport behavior and electrical properties in these compounds have been studied. According to the results of this research, crystallographic distortion is induced by the substitution of smaller ions, Pr or Nd, onto the La-site. Powder $x$-ray diffraction patterns show a crystallographic transition from rhombohedral symmetry (R-3c) to orthorhombic (Pbnm) crystal structure as the doping content is increased. The increase of deformation from R-3c to Pbnm decreases the bond angle of Mn3+¡ÐO2-¡ÐMn4+ , increases the cant of Mn spin, weakens the double-exchange interaction and results in decrease of ferromagnetism, low ferromagnetic transition temperature Tc, eg electron bandwidth and conductivity. However, the great quantity of decrease in resistivity by an external field leads to the increase in the magnetoresistance ratio. We also find that the increase of saturation magnetization results from the contribution of magnetic ion of Pr or Nd. In addition. in contrast to substitution La by magnetic ion of Pr and Nd, the saturation magnetization is decreased as Y content is increased. The zero-field-cool (ZFC) and field-cool (FC) magnetic measurements indicate that the range of spin ordering for Y one is shorter than Pr one or Nd one with the same doping content. It is because of the small ionic radius of Y, which results in larger distortion, increases the bond angle of Mn3+¡ÐO2-¡ÐMn4+, and corresponds low ferromagnetic transition temperature. The distortion induced by Mn-site substitution is not obvious due to the similar radius of Mn, Co and Fe. Powder x-ray diffraction patterns show a single phase of rhombohedral symmetry (R-3c) for Co doped ststem and a slight crystallographic transition from rhombohedral (R-3c) to orthorhombic (Pbnm) symmetry for Fe doped system. Values of temperature dependence of magnetization indicate that the ferromagnetic double-exchange interaction is gradually substituted by the superexchange interaction. The ZFC-FC curves also indicate that long-range spin ordering is progressively substituted by the short-range spin ordering. The substitution of Mn by Co and Fe supresses the double-exchange interaction, decreases the ferromagnetism and the ferromagnetic transition temperature. Due to the synthesis of the substitution of Nd, Pr, Y for La and Co, Fe for Mn, the mechanism of substitution effects are proved different. The substitution of Nd, Pr and Y for La distorts the crystal, decreases the Mn3+¡ÐO2-¡ÐMn4+ bond angle, and results in the transition of properties, while the substitution of Co and Fe for Mn decrease the percentage of ferromagnetic Mn3+¡ÐO2-¡ÐMn4+. The purpose of this thesis is to clear up the role functions of all elements in these compounds and properties of these compounds. Based on the knowledge of these compounds, it would be helpful to control the physical mechanism and improve the characteristics on preparing their thin film devices.