Κ-carraghénane natif et modifié hydrophobement pour moduler les propriétés rhéologiques et structurelles des gels et des émulsions eau-dans-eau

K-carrageenan (κ-car) belongs to an important class of linear sulfated polysaccharides mainly extracted from different species of red seaweed. Its gelling and viscosifying properties make it highly valued in the food, cosmetic, and pharmaceutical industries This thesis explores the molecular and macroscopic modulation of κ-carrageenan (κ-car) gelation properties through chemical modification and polymer–polymer interactions, with the aim of tailoring its rheological behaviour for various applications. The work begins with a systematic investigation of chemically modified κ-car (via acetylation). Acetylation did not significantly impact the molar mass, but resulted in a progressive decrease in intrinsic viscosity, particularly up to a degree of acetylation (DA) of ~15%. At low concentrations, the polyelectrolyte effect remained unchanged, and could be fully screened by ionic strength adjustment (0.1 M NaCl). Gelation studies showed that increasing DA lowered the critical gelation temperature in the presence of KCl, with DA > 19% fully inhibiting gelation at 5 °C. DSC analysis confirmed that acetylation hindered the coil-helix transition, while rheological measurements revealed a sharp decline in gel stiffness, highlighting the disruption of long helical segments essential for crosslinking.The investigation was further expanded to explore how binary mixtures of κ-car with different degrees of acetylation (DA) could be used to tune gelation properties. DSC measurements confirmed that coil-helix transitions occurred independently within the mixtures. At low temperatures, the elastic modulus of the mixed gels showed a linear relationship with composition, aligning with the moduli of the individual components. This suggests that gel strength is governed by the overall number of helices capable of forming crosslinks. High-resolution confocal laser scanning microscopy (CLSM), combined with differential labelling, provided clear evidence of co-aggregation between κ-carrageenan chains with different degrees of acetylation. These results offer a practical framework for finely tuning gelation behaviour via controlled blending.In the final phase, the interaction of κ-car with other water-soluble polymers (PEO, dextran, pullulan, gelatin) was explored both in simple blends and in water-in-water (W/W) emulsion systems in the presence of KCl. Compatible polymers led to more homogeneous κ-car gels without huge impact on its rheological properties. In W/W systems, κ-car partitioned selectively across the phases depending on the polymer combination, impacting microstructure and rheology. While some systems (e.g., Dex/Pul) showed weak partitioning and negligible change in gel strength, others offered new routes to spatially structured gels.Together, these studies provide a comprehensive framework for chemically and physically tuning κ-car properties, offering valuable strategies for the design of soft materials with customizable mechanical and gelation characteristics.