Developing Self-Healing Hydrogel-Composite Membranes for Water Treatment [electronic resource].

9780438902695

Ann Arbor : ProQuest Dissertations & Theses, 2018.

1 online resource (134 p.)

Access is available to the Yale community.

Water filtration membranes are one of the technologies used in water treatment to remove contaminants ranging from suspended particles to multivalent ions. Physical damage to membranes discounts one of their most notable advantages, i.e., providing a near-absolute barrier against pathogens such as viruses that are strictly regulated in potable water production. Current membrane integrity monitoring techniques cannot accurately locate a breach in a membrane system and they do not offer a way to repair the damage, even if it were detectable. Membranes that have the ability to self-heal would bypass the need for membrane replacement practices and recover their original rejection levels autonomously. While most self-healing materials developed thus far suffer from moisture sensitivity or the input of excessive heat that precludes them from being used as membrane materials, one class of materials, hydrogels, avoid these limitations. This dissertation proposes that hydrogel composite membranes provide the necessary combination of permeability and self-healing property to realize the goal of a self-healing membrane. To test the aforementioned hypothesis, hydrogel pore-filled membranes were fabricated via in-situ graft polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto microporous polyethersulfone (PES) substrates. The effect of monomer concentration on the membrane's permeability and selectivity was investigated, followed by physical and chemical characterization of the hydrogel composite membranes. Self-healing tests of the pore-filled membranes showed that the membranes autonomously restore their particle rejection up to 99% from rejection levels as low as 30% after being physically damaged. Covalent attachment of the hydrogel to the substrate was essential for stable membrane performance. The observed self-healing property of the hydrogel-composite membranes is attributed to the latent swelling ability of pore-filling hydrogels and the strong intermolecular diffusion and hydrogen bonding between the hydrogel. While poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) pore-filled membranes exhibited strong self-healing property, the stability of these membranes in high ionic strength solutions was uncertain. As a result, the effect of changes in the ionic strength of the swelling medium due to the presence of saline and acidic solutions on PAMPS pore-filled membranes was investigated. Acidic conditions had a deleterious effect on the pore-filled membranes, resulting in loss of rejection to 50%. However, the presence of cations such as calcium and sodium ions in saline solutions improved the stability and self-healing property of PAMPS pore-filled membranes substantially. Ionically cross-linked membranes showed rejection recovery from values as low as 13%, which is a marked improvement over previous pore-filled membranes which did not show any self-healing property when the rejection fell below 30%. One limitation of PAMPS pore-filled membranes is low permeability due to the thickness of the active-layer that spans the membrane cross-section. This can be improved by limiting the modification depth of the PES support to create a more asymmetrically pore-filled structure but the effect that such a change in membrane configuration has on the self-healing property of the membranes is unknown. To investigate the effect, asymmetrically pore-filled membranes were fabricated by increasing the viscosity of the AMPS monomer solution and limiting its penetration into the PES substrate. The membranes maintained their self-healing property, exhibiting final rejection values as high as 98%. Confocal laser scanning microscope (CLSM) images of healed asymmetrically pore-filled membranes showed that the swelling degree of the PAMPS hydrogel is limited to one side of the membranes, providing further evidence that latent swelling of the pore-filling hydrogel is a crucial part of the self-healing mechanism in hydrogel composite membranes.

Dissertations & Theses @ Yale University.

Books / Online / Dissertations & Theses

English

August 21, 2019

Thesis (Ph.D.)--Yale University, 2018.

Yale University.