Structural Characterization of Porous Materials: Understanding Mass Transport through Asymmetric Membranes during Forward Osmosis

Engineered osmosis (EO) is an emerging membrane separations-based technology platform comprising of forward osmosis, pressure-retarded osmosis, and direct osmotic dilution/concentration processes. EO relies on a water flux driven across a semi-permeable membrane as a result of osmotic pressure gradients between two solutions, the relatively dilute feed and a concentrated draw solution. However, the support layer in EO membranes presents a resistance to solute transport resulting in internal concentration polarization (ICP) phenomena which results in the actual driving force being far lower than what is available. Severity of ICP is largely influenced by the structure of the support layer in the composite EO membranes. The successful commercialization of EO requires, among other key factors, tailoring of membranes with optimum structures. To this end, there is a flurry of research on the fabrication of novel membranes but no adequate methods to characterize and understand how these structures affect membrane transport. This thesis is among the first few to present efforts to comprehensively characterize EO membrane structures and understand how they relate to transport. New approaches to soft materials characterization have been developed and limitations of traditional approaches have been convincingly proved. Numerical simulation studies have been employed to inform future membrane designers on optimal structures for transport. It is believed that this work is an important step towards understanding and optimizing membrane structure for separations technologies, especially forward osmosis.