Fundamentals and Fabrication of Polymeric Membranes for Engineered Osmosis Processes

Abstract

The main challenges in the low-energy and low-fouling engineered osmosis processes include the material development and morphology design of the membranes. This dissertation has revealed the structure ?property relationships of materials, the subsequent membrane formation mechanism for forward osmosis (FO), and the morphology design as well as post treatment for improved membrane performance for desalination and osmotic power generation. It has been discovered that the wet-state free volume is highly dependent on the hydrophilicity of the polymers, and the water and salt transport properties are positively linked to the wet-state free volume. During the membrane formation process, the surface chemistry of the membrane and casting substrate has been found to play key roles in determining the structure of the bottom selective layer formed between them two. By carefully designing the casting parameters, double-dense layer membranes with minimized internal concentration polarization (ICP), enhanced water permeability and less fouling have been fabricated by phase inversion. The substrate properties and post treatment conditions for thin film composite (TFC) membranes have been studied as well, and membranes with good mechanical strength and high power density have been obtained for osmotic power generation.