Stabilizing Bicontinuous Emulsions with Sub-Micrometer Domains Solely by Nanoparticles.

Nanoparticle-stabilized, bicontinuous interfacially jammed emulsion gels (bijels) find potential applications as battery, separation membrane, and chemical reactor materials. Decreasing the liquid domain sizes of bijels to sub-micrometer dimensions requires surfactants, complicating bijel synthesis and postprocessing into functional nanomaterials. This work introduces surfactant-free bijels with sub-micrometer domains, solely stabilized by nanoparticles. To this end, the covalent surface functionalization of silica nanoparticles is characterized by thermogravimetric analysis, mass spectrometry, Fourier-transform infrared spectroscopy, and contact angle measurements. Bijels are generated with the functionalized nanoparticles via solvent transfer induced phase separation (STrIPS), enabling the optimization of nanoparticle functionalization and surface ionization. Nanoparticles of intermediate functionalization and controlled negative surface charge stabilize bijels with sub-micrometer liquid domains. This remarkable control over bijel synthesis provides urgently needed progress to facilitate the widespread implementation of bijels as nanomaterials in research and applications.

Dual access to the fluid networks of colloid-stabilized bicontinuous emulsions through uninterrupted connections.

Large surface areas are important for enhancing mass and energy transfer in biological and technological processes. Bicontinuous interfacially jammed emulsion gels (bijels) increase the surface area between two fluids by intertwining them into particle stabilized networks. To facilitate efficient mass and energy exchange via the bijels' high surface area, the fluid networks need to be connected to their respective bulk phases. Here, we generate bijels between two bulk fluids and investigate the connections the bijel makes. We analyze these connections by investigating the colloidal stability, interfacial rheology and mass transfer dynamics during bijel formation. To this end, we employ confocal and electron microscopy, as well as dynamic light scattering, pendant drop analysis, electrophoretic mobility measurements and diffusion simulations. We find that the connections the bijel makes to the bulk fluid can be disrupted by severe colloidal aggregation and interruptions of the bicontinuous fluid network. However, the addition of alcohol to the bulk fluid moderates aggregation and allows undisturbed fluid network formation, facilitating open connections between bijel and bulk fluid. The unprecedented control of bijel pore connections from this research will be crucial for the application of bijels as separation membranes, electrochemical energy storage materials and chemical reactors.