Exploring the formation of nanoparticle-modified separation membranes from emulsion gels

Climate change and population growth are putting immense pressure on natural water resources. To produce clean water for daily life, porous separation membranes are needed. However, traditional separation membranes made of polymers are susceptible to fouling and chemical degradation, compromising filtration properties. Recently, bicontinuous interfacially jammed emulsion gels (bijels) have been introduced as robust membrane material with nanoparticle-covered surfaces that enhance stability. However, their formation via liquid/liquid phase separation and nanoparticle self-assembly involves complex interfacial stabilization mechanisms, which need to be controlled to produce bijel separation membranes. In this thesis, we hypothesize that surface tension and particle wettability are the key drivers in interfacial bijel stabilization. To test our hypothesis and produce functional bijel membranes, we study the effect of liquid composition on surface tension and particle self-assembly during bijel synthesis via solvent transfer induced phase separation (STrIPS; Chapter 2). Revealing how the liquid composition governs the bijel structure, the fabrication of flat-sheet bijels via roll-to-roll film coating is introduced (Chapter 3). As these STrIPS-bijel films are made using surfactant-modified nanoparticles, we detail how the simultaneous presence of surfactants and particles at liquid/liquid interfaces affects the rigidity of colloidal assemblies in bijel stabilization (Chapter 4). To refine control over the bijel structure in roll-to-roll coating, we analyze how substrate wetting affects the membrane uniformity (Chapter 5). Building on the resulting understanding of the self-assembly and bijel formation kinetics, we demonstrate the application of bijels for filtration with controlled selectivity and pH-responsive flux. The fundamental insights into non-equilibrium bijel formation combined with scalable membrane fabrication and filtration testing open new avenues for designing robust bijel membranes for sustainable water treatment.