Self-assembled hydrogels using biobased amphiphiles and their potential applications

Overview & Synopsis

Low-molecular weight (LMW) gels have emerged as promising alternatives to polymeric gels due to their reversibility, responsiveness to stimuli, and tunable molecular design. While most known LMW gelators with rigid backbones typicallly form fibrillar networks, surfactants generally give rise to gels with micellar, vesicular or lamellar structures. Interestingly, microbial biosurfactants, eco-friendly alternatives of oil-based surfactants, have recently been shown to self-assemble into fibrillar networks, a feature traditionally associated with LMW gelators. This intriguing behavior remains largely unexplored. This thesis investigates the gelation behavior of a range of microbial biosurfactants, including glycolipids and lipopeptides, with a particular focus on their self-assembly response to metal cations. Through a systematic study combining rheology, small angle scattering and microscopy, we identify the conditions under which some biosurfactants form gels, and we characterize their resulting nanostructures. Notably, we report the formation of mycosubtilin organogels, via a solvent switch method and surfactin hydrogels upon slow acidification. Beyond understanding the gelation mechanisms, this work explores functional applications of biosurfactant gels. Using a silver-coordinated glycolipid-based fibrillar gel as a template, silver nanoparticles and nanowires are synthesized in situ, by controlling the reduction kinetics. Upon nanowire formation, the resulting hybrid gel exhibits electronic conductivity, as confirmed by impedance spectroscopy. Overall, this thesis expands the library of biosurfactant-based LMW gels, provides insights into their molecular self-assembly, and demonstrates their potential for advanced applications in nanomaterials and soft electronics.