Looking into the structure of bijel templated membranes

Abstract

Desalination of seawater is an increasingly necessary process as climate change and population growth are making fresh water more scarce. The high energy requirements of this process can be reduced using membrane technology. Solvent transfer induced phase separation (STrIPS) is a recent approach to make porous membranes. In this method spindodal decomposition of oil and water is induced by removal of a solvent. This results in two intertwined and continuous phases with high interfacial area, of which the structure mechanically jammed by self-assembly of nanoparticles on the interface. We use the monomeric (1,4-butanediol diacrylate (BDA)), which is polymerized to obtain a solid membrane. The aim of this work is to investigate if we can continuously produce thin-film bijel-templated membranes with a controllable structure, and if we can understand the mechanism of the formation of their structure. We look have looked into the production process by first building a roll-to-roll processing machine that is able to continuously produce the membranes, and by investigating the wetting behaviour of precursor mixtures on the substrate. The membrane structure and its formation mechanism were investigated by varying parameters such as nanoparticle concentration and surface chemistry, and by arresting phase separation at different time steps. The resulting structures were visualized using Laser Scanning Confocal Microscopy (LSCM) and Scanning Electron Microscopy (SEM). With this research, we have improved the roll-to-roll fabrication method and have found how precursor composition which wet the substrate better result in membranes with a more homogeneous morphology. We learned how we can introduce vertical channels into the membrane structure by increasing the particle hydrophobicity, and how the pore size gradient can be decreased by increasing nanoparticle concentration. Furthermore, by tracking the structural evolution, we have found how phase separation progresses through the membranes, and how the surface pores are a deciding factor in formation process.