Le développement des lasers de puissance engendre un intérêt pour la recherche de matériaux présentant des propriétés optiques non linéaires (ONL). Les matériaux vitreux sont de très bons candidats puisqu’ils peuvent être transparents et élaborés en grandes dimensions. La précipitation de particules non centro-symétrique dans un verre permet d’engendrer cette propriété en volume, et d’ingérer facilement ce matériau dans les dispositifs lasers. Dans ce contexte, cette thèse présente les résultats obtenus sur la précipitation de la phase LiNO3 dans la matrice vitreuse 35 Li2O- 25 Nb2O5- 40 SiO2. Le mécanisme de cristallisation de cette phase est étudié par analyse thermique, imagerie optique et électronique ainsi que par une analyse in-situ. Ces analyses mettent en évidence une cristallisation sphérolitique du niobate de lithium dans ce verre, conduisant à l’obtention de vitrocéramiques. Les propriétés optiques non linéaires d’ordre deux sont mesurés sur ces matériaux. Un signal original et isotrope de Génération de Second Harmonique a été mesuré. Une analyse multi-échelle permet une meilleure compréhension et une corrélation entre la structure des sphérolites et l’origine de la génération d’un tel signal. Le modèle développé suite à ces analyses permet d’entrevoir le développement de nouveaux matériaux micro-composites à propriétés ONL isotropes. / The high power laser development required the need of materials with nonlinear properties. Glass materials can be considered as ideal materials as they can be transparent and elaborated in very large dimension. Precipitation of non-centro symmetric crystalline particles in bulk glass leads to a material with bulk nonlinear properties. This glass-ceramic should be then easily integrated in such laser facilities. In this thesis, the results concerning the precipitation of the LiNO3 phase in the glassy-matrix 35 Li2O- 25 Nb2O5- 40 SiO2 are detailed. The crystallization mechanism of this phase is studied through thermal analysis, optical and electronic microscopy as well as in-situ analyses. These studies reveal glass-ceramics are obtained through a precipitation of the lithium niobate crystalline phase in spherulite shape. The nonlinear optical properties are investigated on this materials and an original, isotropic Second Harmonic Generation signal (SHG) is registered in the bulk glass-ceramic. A complete study using a multi-scale approach allows the correlation between the spherulite structure and the nonlinear optical properties. A mechanism at the origin of the SHG signal is proposed. This leads to a new approach for transparent inorganic materials development for isotropic SHG conversion.

Narrow molecular weight fractions of Poly(ε-caprolactone) were successfully obtained using the successive precipitation fractionation technique with toluene/n-heptane as a solvent/nonsolvent pair. Calorimetric studies of the melting behavior of fractions that were crystallized either isothermally or under constant cooling rate conditions suggested that the isothermal crystallization of the samples should be used for a proper evaluation of the molecular weight dependence of the observed melting temperature and degree of crystallinity in PCL. The molecular weight and temperature dependence of the spherulitic growth rate of fractions was studied in the context of the Lauritzen-Hoffman two-phase model and the Strobl three-phase model of polymer crystallization. The zero-growth rate temperatures, determined from spherulitic growth rates using four different methods, are consistent with each other and increase with chain length. The concomitant increase in the apparent secondary nucleation constant was attributed to two factors. First, for longer chains there is an increase in the probability that crystalline stems belong to loose chain-folds, hence, an increase in fold surface free energy. It is speculated that the increase in loose folding and resulting decrease in crystallinity with increasing chain length are associated with the ester group registration requirement in PCL crystals. The second contribution to the apparent nucleation constant arises from chain friction associated with segmental transport across the melt/crystal interface. These factors were responsible for the much stronger chain length dependence of spherulitic growth rates at fixed undercooling observed here with PCL than previously reported for PE and PEO. In the case of PCL, the scaling exponent associated with the chain length dependence of spherulitic growth rates exceeds the upper theoretical bound of 2 predicted from the Brochard-DeGennes chain pullout model. Observation that zero-growth and equilibrium melting temperature values are identical with each other within the uncertainty of their determinations casts serious doubt on the validity of Strobl three-phase model. A novel method is proposed to determine the Porod constant necessary to extrapolate the small angle X-ray scattering intensity data to large scattering vectors. The one-dimensional correlation function determined using this Porod constant yielded the values of lamellar crystal thickness, which were similar to these estimated using the Hosemann-Bagchi Paracrystalline Lattice model. The temperature dependence of the lamellar crystal thickness was consistent with both LH and the Strobl model of polymer crystallization. However, in contrast to the predictions of Strobl’s model, the value of the mesomorph-to-crystal equilibrium transition temperature was very close to the zero-growth temperature. Moreover, the lateral block sizes (obtained using wide angle X-ray diffraction) and the lamellar thicknesses were not found to be controlled by the mesomorph-to-crystal equilibrium transition temperature. Hence, we concluded that the crystallization of PCL is not mediated by a mesophase. Metallocene-catalyzed linear low-density (m-LLDPE with 3.4 mol% 1-octene) and conventional low-density (LDPE) polyethylene blends of different compositions were investigated for their melt-state miscibility and concurrent crystallization tendency. Differential scanning calorimetric studies and morphological studies using atomic force microscopy confirm that these blends are miscible in the melt-state for all compositions. LDPE chains are found to crystallize concurrently with m-LLDPE chains during cooling in the m-LLDPE crystallization temperature range. While the extent of concurrent crystallization was found to be optimal in blends with highest m-LLDPE content studied, strong evidence was uncovered for the existence of a saturation effect in the concurrent crystallization behavior. This observation leads us to suggest that co-crystallization, rather than mere concurrent crystallization, of LDPE with m-LLDPE can indeed take place. Matching of the respective sequence length distributions in LDPE and m-LLDPE is suggested to control the extent of co-crystallization. / Ph. D.

The crystallization and melting behaviors of an ethylene/1-hexene copolymer and series of narrow molecular weight linear polyethylene and poly(ethylene oxide) fractions were studied using a combination of ultra-fast and conventional differential scanning calorimetry, optical microscopy, small angle X-ray scattering, and wide angle X-ray diffraction. In the case of linear polyethylene and poly(ethylene oxide), the zero-entropy production melting temperatures of initial lamellae of isothermally crystallized fractions were analyzed in the context of the non-linear Hoffman-Weeks method. Using the Huggins equation, limiting equilibrium melting temperatures of 141.4 ± 0.8oC and 81.4 ± 1.0oC were estimated for linear polyethylene and poly(ethylene oxide), respectively. The former and the latter are about 4oC lower and 12.5oC higher than these predicted by Flory/Vrij and Buckley/Kovacs, respectively. Accuracy of the non-linear Hoffman-Weeks method was also examined using initial lamellar thickness literature data for a linear polyethylene fraction at different crystallization temperatures. The equilibrium melting temperature obtained by the Gibbs-Thomson approach and the C2 value extracted from the initial lamellar thickness vs. reciprocal of undercooling plot were similar within the limits of experimental error to those obtained here through the non-linear Hoffman-Weeks method. In the next step, the Lauritzen-Hoffman (LH) secondary nucleation theory was modified to account for the effect of stem length fluctuations, tilt angle of the crystallized stems, and temperature dependence of the lateral surface free energy. Analysis of spherulite growth rate and wide angle X-ray diffraction data for 26 linear polyethylene and 5 poly(ethylene oxide) fractions revealed that the undercooling at the regime I/II transition, the equilibrium fold surface free energy, the strength of the stem length fluctuations and the substrate length at the regime I/II transition are independent of chain length. The value of the equilibrium fold surface free energy derived from crystal growth rate data using the modified Lauritzen-Hoffman theory matches that calculated from lamellar thickness and melting data through the Gibbs-Thomson equation for both linear polyethylene and poly(ethylene oxide). Larger spherulitic growth rates for linear polyethylene than for poly(ethylene oxide) at low undercooling is explained by the higher secondary nucleation constant of poly(ethylene oxide). While the apparent friction coefficient of a crystallizing linear polyethylene chain is 2 to 8 times higher than that of a chain undergoing reptation in the melt state, the apparent friction coefficient of a crystallizing poly(ethylene oxide) chain is about two orders of magnitude lower. This observation suggests that segmental mobility on the crystal phase plays a significant role in the crystal growth process. In case of the statistical ethylene/1-hexene copolymer, the fold surface free energies of the copolymer lamellae at the time of crystallization and melting increase with increasing undercooling, approaching the same magnitude at high undercooling. As a result of this temperature dependence, the experimental melting vs. crystallization temperature plot is parallel to the Tm = Tc line and the corresponding Gibbs-Thomson plot is non-linear. This behavior is attributed to the fact that longer ethylene sequences form a chain-folded structure with lower concentration of branch points on the lamellar surface at lower undercooling, while shorter ethylene sequences form lamellar structures at higher undercooling exhibiting a higher concentration of branch points on the lamellar surface. Branch points limit the ability of lamellar structures to relax their kinetic stem-length fluctuations during heating prior to melting. / Ph. D. / Morphology of semi-crystalline polymers is strongly affected by their crystallization conditions. Thermodynamic and kinetic models allow us to understand the crystallization mechanism of a semi-crystalline polymer and relate its crystallization conditions to the final morphology. In this research, we studied the molar mass dependence of the crystallization and melting behaviors of narrow molecular weight distribution linear polyethylene (LPE) and poly(ethylene oxide) (PEO) fractions using a modified Lauritzen-Hoffman (LH) secondary nucleation theory. We have shown that the equilibrium melting temperature of LPE and PEO fractions found from the non-linear Hoffman-Weeks method are within the experimental uncertainty identical with these measured directly for extended chain crystals or derived from a Gibbs-Thomson analysis. The value of the equilibrium fold surface free energy derived from crystal growth rate data using the modified LH theory matches that calculated from lamellar thickness and melting data through the Gibbs-Thomson equation for both LPE and PEO. We reported that the higher segmental mobility of PEO in the crystalline phase leads to significantly lower apparent chain friction coefficients during crystal growth compared to LPE. We also studied the role of short-chain branching in the crystal growth kinetics of ethylene/1-hexene copolymers. We observed that the fold surface free energies during crystallization and during melting are both function of the undercooling while the ratio of the former to the latter decreases with increasing undercooling. We proposed that this behavior may be related to the concentration of short-chain branches at the surface of the lamellae, where higher concentration leads to lower relaxation.

Part of the research described in this thesis is conducted in collaboration with Centre d' étude et de Recherche sur les Macromolécules (CERM), Université de Liège, Sart-Tilman, Belgium / Les copolymères séquencés amphiphiles sont très prometteurs pour des applications de technologie de pointe en raison de leur capacité à s'auto-assembler dans des structures bien organisées à l'échelle du micro– et du nanométre, et de leur sensibilité à des stimulations de différentes natures. La formation des nanomotifs bien ordonnés dans les films et/ou en masse fournit un substitut à la nanolithographie et est utile pour le design et l'ingénierie de nanomembranes et de matériaux nanoporeux. L'auto–assemblage dans des solvants sélectifs, en incluant la sensibilité au pH et à la température, peut être ajusté pour correspondre aux besoins de différentes applications biomédicales, telles que l’encapsulation et/ou relargage de médicaments, l'ingénierie de tissus, etc. Dans ce contexte, des copolymères séquencés de type L–lactide (LLA) et méthacrylate 2–diméthylaminoéthyl (DMAEMA) sont d’un grand intérêt. Comme le contrôle sur l'auto–assemblage des copolymères séquencés est permis au niveau moléculaire, il est très important de préparer des copolymères bien définis avec des longueurs de bloc prévisibles et de faible polydispersité. Ainsi, une partie de cette étude a été consacrée au développement de procédures synthétiques optimales et à la caractérisation détaillée de copolymères di– et triblocs de LLA et de PDMAEMA. Un outil simple pour déterminer la présence d'homo–PLLA résiduel a été développée; cela a permis de déterminer et d'expliquer plusieurs voies de synthèse indésirables. La dernière inclut la participation possible de l'amorceur bifonctionnel utilisé, et nous avons alors proposé un système alternatif d'amorceur bifonctionnel/catalyseur. La racémisation du LLA par les unités amine de (P)DMAEMA a été observée pendant la polymérisation, limitant ainsi l'utilisation première du bloc PDMAEMA pour la préparation des copolymères PLLA–b–PDMAEMA. Les études thermiques et de cristallisation, en incluant les copolymères séquencés partiellement quaternisés, ont révélé un retard significatif de la vitesse de cristallisation, en présence du bloc de PDMAEMA. Nous avons constaté que les blocs sont miscibles pour de faibles masses molaires et que la miscibilité partielle est maintenue après quaternisation. Selon la longueur et le taux de quaternisation du bloc PDMAEMA, la cristallisation du PLLA a été étudiée dans un environnement restreint et confiné, faiblement ou fortement. La torsion des lamelles cristallines observée pour certains copolymères biséquencés a été accentuée dans les copolymères triséquencés, où la formation de sphérolites annelés a été observée dans toutes les conditions thermiques utilisées. / Multi–functional amphiphilic block copolymers have much promise for various high technology applications thanks to the controlled stimuli–responsive self–assembly into well–organized structures on the micro– and nanometer scales. The formation of well–ordered nanopatterns in films and/or in bulk provides a competitive substitute to nanolithography and is useful in the design and engineering of nanomembranes and nanoporous materials. Solution self–assembly in selective solvents, including pH and temperature sensitivity, can be tuned to match the needs of different biomedical applications, such as drug encapsulation/delivery, tissue engineering, etc. In this context, block copolymers of L–lactide (LLA) and 2–dimethylaminoethyl methacrylate (DMAEMA) are of great interest. Since the control over self–assembly of block copolymer systems is enabled on a molecular level, it is of great importance to prepare well–defined block copolymers with predictable block lengths and low polydispersity. Thus, a major part of the research in this study was devoted to developing optimal synthetic procedures with detailed characterization of linear di– and triblock copolymers of LLA and PDMAEMA. A simple tool to determine homo–PLLA impurity was developed, which helped to determine and explain several undesired routes. The latter includes possible involvement of the bifunctional initiator used, and an alternative bifunctional initiator/catalyst system was proposed. Racemization of LLA by (P)DMAEMA moieties was observed during LLA polymerization thus limiting the utilization of PDMAEMA–first approach for the preparation of PLLA–b–PDMAEMA. Thermal and crystallization studies, including on quaternized block copolymers, revealed a significant retardation effect of the PDMAEMA block on the crystallization kinetics. The blocks were found to be miscible in the melt at low molecular weights, and maintained partial miscibility after quaternization. Depending on the length and the quaternization degree of PDMAEMA, PLLA crystallization was studied in a templated, soft or hard confinement environment. Crystalline lamellae twisting observed in certain diblock copolymers was facilitated in triblock copolymers, where the formation of banded spherulites was observed in all thermal conditions used.

Les copolymères séquencés amphiphiles sont très prometteurs pour des applications de technologie de pointe en raison de leur capacité à s'auto-assembler dans des structures bien organisées à l'échelle du micro– et du nanométre, et de leur sensibilité à des stimulations de différentes natures. La formation des nanomotifs bien ordonnés dans les films et/ou en masse fournit un substitut à la nanolithographie et est utile pour le design et l'ingénierie de nanomembranes et de matériaux nanoporeux. L'auto–assemblage dans des solvants sélectifs, en incluant la sensibilité au pH et à la température, peut être ajusté pour correspondre aux besoins de différentes applications biomédicales, telles que l’encapsulation et/ou relargage de médicaments, l'ingénierie de tissus, etc. Dans ce contexte, des copolymères séquencés de type L–lactide (LLA) et méthacrylate 2–diméthylaminoéthyl (DMAEMA) sont d’un grand intérêt. Comme le contrôle sur l'auto–assemblage des copolymères séquencés est permis au niveau moléculaire, il est très important de préparer des copolymères bien définis avec des longueurs de bloc prévisibles et de faible polydispersité. Ainsi, une partie de cette étude a été consacrée au développement de procédures synthétiques optimales et à la caractérisation détaillée de copolymères di– et triblocs de LLA et de PDMAEMA. Un outil simple pour déterminer la présence d'homo–PLLA résiduel a été développée; cela a permis de déterminer et d'expliquer plusieurs voies de synthèse indésirables. La dernière inclut la participation possible de l'amorceur bifonctionnel utilisé, et nous avons alors proposé un système alternatif d'amorceur bifonctionnel/catalyseur. La racémisation du LLA par les unités amine de (P)DMAEMA a été observée pendant la polymérisation, limitant ainsi l'utilisation première du bloc PDMAEMA pour la préparation des copolymères PLLA–b–PDMAEMA. Les études thermiques et de cristallisation, en incluant les copolymères séquencés partiellement quaternisés, ont révélé un retard significatif de la vitesse de cristallisation, en présence du bloc de PDMAEMA. Nous avons constaté que les blocs sont miscibles pour de faibles masses molaires et que la miscibilité partielle est maintenue après quaternisation. Selon la longueur et le taux de quaternisation du bloc PDMAEMA, la cristallisation du PLLA a été étudiée dans un environnement restreint et confiné, faiblement ou fortement. La torsion des lamelles cristallines observée pour certains copolymères biséquencés a été accentuée dans les copolymères triséquencés, où la formation de sphérolites annelés a été observée dans toutes les conditions thermiques utilisées. / Multi–functional amphiphilic block copolymers have much promise for various high technology applications thanks to the controlled stimuli–responsive self–assembly into well–organized structures on the micro– and nanometer scales. The formation of well–ordered nanopatterns in films and/or in bulk provides a competitive substitute to nanolithography and is useful in the design and engineering of nanomembranes and nanoporous materials. Solution self–assembly in selective solvents, including pH and temperature sensitivity, can be tuned to match the needs of different biomedical applications, such as drug encapsulation/delivery, tissue engineering, etc. In this context, block copolymers of L–lactide (LLA) and 2–dimethylaminoethyl methacrylate (DMAEMA) are of great interest. Since the control over self–assembly of block copolymer systems is enabled on a molecular level, it is of great importance to prepare well–defined block copolymers with predictable block lengths and low polydispersity. Thus, a major part of the research in this study was devoted to developing optimal synthetic procedures with detailed characterization of linear di– and triblock copolymers of LLA and PDMAEMA. A simple tool to determine homo–PLLA impurity was developed, which helped to determine and explain several undesired routes. The latter includes possible involvement of the bifunctional initiator used, and an alternative bifunctional initiator/catalyst system was proposed. Racemization of LLA by (P)DMAEMA moieties was observed during LLA polymerization thus limiting the utilization of PDMAEMA–first approach for the preparation of PLLA–b–PDMAEMA. Thermal and crystallization studies, including on quaternized block copolymers, revealed a significant retardation effect of the PDMAEMA block on the crystallization kinetics. The blocks were found to be miscible in the melt at low molecular weights, and maintained partial miscibility after quaternization. Depending on the length and the quaternization degree of PDMAEMA, PLLA crystallization was studied in a templated, soft or hard confinement environment. Crystalline lamellae twisting observed in certain diblock copolymers was facilitated in triblock copolymers, where the formation of banded spherulites was observed in all thermal conditions used. / Part of the research described in this thesis is conducted in collaboration with Centre d' étude et de Recherche sur les Macromolécules (CERM), Université de Liège, Sart-Tilman, Belgium