The understanding of thermodynamic glass transition has been hindered by the lack of proper models beyond mean-field theories. Here, we propose a three-dimensional lattice glass model on a simple cubic lattice that exhibits the typical dynamics observed in fragile supercooled liquids such as two-step relaxation, super-Arrhenius growth in the relaxation time, and dynamical heterogeneity. Using advanced Monte Carlo methods, we compute the thermodynamic properties deep inside the glassy temperature regime, well below the onset temperature of the slow dynamics. The specific heat has a finite jump towards the thermodynamic limit with critical exponents close to those expected from the hyperscaling and the random first-order transition theory for the glass transition. We also study an effective free energy of glasses, the Franz-Parisi potential, as a function of the overlap between equilibrium and quenched configurations. The effective free energy indicates the existence of a first-order phase transition, consistent with the random first-order transition theory. These findings strongly suggest that the glassy dynamics of the model has its origin in thermodynamics.

Les excitons indirects dipolaires, sont des quasi-particules bosoniques dans les semi-conducteurs, composés d'un électron et d'un trou spatialement séparés mais toujours liés par interaction coulombienne. Leur grande durée de vie radiative et leur capacité à se déplacer sur de grandes distances avant leur recombinaison en font un système unique qui peut être à la fois optiquement actif mais également électriquement contrôlable. Ce système permet l'étude des propriétés fondamentales de la lumière et de la matière, mais aussi le développement de dispositifs excitoniques conceptuellement nouveaux. Les excitons dans les puits quantiques polaires en nitrure de gallium (GaN) peuvent être considérés comme des excitons naturellement indirects, en raison du fort champ électrique intrinsèque existant dans la direction de croissance cristalline. Cette thèse est consacrée à l'étude expérimentale et une étude des excitons indirects dans des hétérostructures GaN/(Al,Ga)N, ainsi que les états collectifs, depuis la conception et la fabrication jusqu'à la spectroscopie optique de leurs états collectifs.Les principaux résultats de ce travail sont (i) la démonstration du confinement spatial dans le plan et du refroidissement des excitons indirects, lorsqu'ils sont piégés dans le potentiel électrostatique créé par des électrodes semi-transparentes de géométries diverses soigneusement conçues et déposées sur la surface de l'échantillon, qui est une condition préalable à l'étude du diagramme de phase complexe de ces bosons dipolaires à basse température ; (ii) la preuve de principe du contrôle électrique des densités et des flux d'excitons indirects dans le plan du puits quantique. Cela ouvre des perspectives intéressantes pour la réalisation de dispositifs excitoniques ; (iii) les premiers points sur le diagramme de phase des bosons dipolaires, fournissant une première mise en évidence non seulement de l'existence d'un phase fortement corrélée résultant des corrélations induites à forte densité (phase de liquide dipolaire) mais aussi la dissociation (transition de Mott) de ces excitons indirects dans les hétérostructures GaN/(Al,Ga)N.

We investigate the delayed rupture of biopolymer gels under a constant shear load by simultaneous dynamic light scattering and rheology measurements. We unveil the crucial role of normal stresses built up during gelation: All samples that eventually fracture self-weaken during the gelation process, as revealed by a partial relaxation of the normal stress concomitant to a burst of microscopic plastic rearrangements.Upon applying a shear stress, weakened gels exhibit in the creep regime distinctive signatures in their microscopic dynamics, which anticipate macroscopic fracture by up to thousands of seconds. The dynamics in fracturing gels are faster than those of nonfracturing gels and exhibit large spatiotemporal fluctuations. A spatially localized region with significant plasticity eventually nucleates, expands progressively, and finally invades the whole sample, triggering macroscopic failure.

Biological activities of cells such as survival and differentiation processes are mainly maintained by a specific extracellular matrix (ECM). Hydrogels have recently been employed successfully in tissue engineering applications. In particular, scaffolds made of gelatin methacrylate-based hydrogels (GelMA) showed great potential due to their biocompatibility, biofunctionality, and low mechanical strength. The development of a hydrogel having tunable and appropriate mechanical properties as well as chemical and biological cues was the aim of this work. A synthetic and biological hybrid hydrogel was developed to mimic the biological and mechanical properties of native ECM. A combination of gelatin methacrylate and acrylamide (GelMA-AAm)-based hydrogels was studied, and it showed tunable mechanical properties upon changing the polymer concentrations. Different GelMA-AAm samples were prepared and studied by varying the concentrations of GelMA and AAm (AAm2.5% + GelMA3%, AAm5% + GelMA3%, and AAm5% + GelMA5%). The swelling behavior, biodegradability, physicochemical and mechanical properties of GelMA-AAm were also characterized. The results showed a variation of swelling capability and a tunable elasticity ranging from 4.03 to 24.98 kPa depending on polymer concentrations. Moreover, the podocyte cell morphology, cytoskeleton reorganization and differentiation were evaluated as a function of GelMA-AAm mechanical properties. We concluded that the AAm2.5% + GelMA3% hydrogel sample having an elasticity of 4.03 kPa can mimic the native kidney glomerular basement membrane (GBM) elasticity and allow podocyte cell attachment without the functionalization of the gel surface with adhesion proteins compared to synthetic hydrogels (PAAm). This work will further enhance the knowledge of the behavior of podocyte cells to understand their biological properties in both healthy and diseased states.