MXenes aan water-olie interfases: van interfase-eigenschappen tot geleidende emulsies

Two-dimensional nanosheets such as MXenes have recently emerged as promising interfacial stabilizers for Pickering emulsions, offering new opportunities to fabricate multiphase materials with tailored mechanical and functional properties. In Pickering emulsions, solid particles adsorb at fluid-fluid interfaces, forming an interfacial layer that enhances emulsion stability and allows direct control over the structure and rheological behavior of the emulsion. This interfacial assembly is particularly attractive for the design of functional materials, as it enables the spatial organization of active components at droplet interfaces and the formation of interconnected networks throughout the system. Among the various two-dimensional materials explored for this purpose, Ti_3C_2$T_x MXenes have attracted significant interest. Their high aspect ratio, combined with intrinsic electrical conductivity, makes them especially appealing as building blocks for conductive emulsions and emulsion-templated materials. For these systems, emulsion templating represents an appealing strategy for fabricating composite materials for applications such as flexible sensors, electromagnetic interference shielding, and energy storage. In particular, the confinement and segregation of conductive nanosheets at the interface allow high interfacial coverage to be achieved at relatively low particle loadings, thereby enhancing electrical performance. In this context, the performance of MXene-based emulsions and emulsion-templated materials depends on how the nanosheets assemble and organize at fluid-fluid interfaces. However, despite their growing use, a fundamental understanding of how MXene nanosheets assemble at fluid-fluid interfaces and how this interfacial organization governs droplet dynamics, emulsion stability, and electrical properties remains limited. Addressing these gaps is essential for the rational design of MXene-stabilized emulsions and their translation into functional materials. This thesis establishes a multiscale framework linking the interfacial assembly and rheology of MXene nanosheets at water-oil interfaces to droplet-scale dynamics and macroscopic emulsion behavior. At the interfacial scale, the adsorption of Ti_3C_2T_x MXenes at water-oil interfaces is enabled by the presence of surfactants, which mediate the interfacial activity of the inherently hydrophilic MXenes. The surfactants adsorb at the oil-water interface and form complexes with the MXene nanosheets through electrostatic interactions, effectively anchoring the nanosheets to the interface. This surfactant-mediated complexation facilitates the formation of multilayered, viscoelastic interfacial networks. Systematic interfacial rheological measurements demonstrate how surface coverage and the structure of the nanosheet-surfactant complexes govern the transition from viscous to elastic behavior and dictate the linear and nonlinear interfacial response. At the single-droplet scale, the impact of interfacial viscoelasticity on droplet dynamics under shear flow is investigated. MXene-covered droplets display markedly altered deformation, breakup, and retraction behavior compared to clean or surfactant-stabilized interfaces, highlighting deviations from classical droplet dynamics models. In addition, the coalescence of isolated MXene-laden droplets is examined under quiescent conditions demonstrating how interfacial elasticity can delay or arrest coalescence, and a microfluidic approach is proposed for future investigation of coalescence under flow. At the emulsion scale, MXene-based Pickering emulsions are studied as conductive multiphase materials in which interfacial assembly directly couples bulk rheological and electrical responses. Combined rheological and dielectric measurements reveal how the connectivity of MXene networks at droplet interfaces together with droplet-droplet interactions control the emulsion rheological properties and charge transport. The formation of percolating interfacial networks gives rise to simultaneous mechanical reinforcement and electrical conductivity, while shear-induced restructuring of the emulsion microstructure leads to reversible changes in both viscoelastic moduli and conductive pathways. Overall, this thesis provides fundamental insight into the role of 2D nanosheet assembly at fluid-fluid interfaces and demonstrates how interfacial rheological properties can be exploited to control droplet dynamics and functional properties in MXene-based Pickering emulsions. These findings contribute to a better understanding of the design of conductive multiphase materials through interfacial engineering.