Date of Award

Summer 8-19-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Biomedical Sciences

Advisor

Caitlin Howell

Second Committee Member

Sue Ishaq

Third Committee Member

Richard Corey

Abstract

In the purification of water and air, membrane fouling is an ongoing issue that leads to the reduction of filter efficiency over time. An increase in the frequency of current chemical and mechanical cleaning methods increases system downtime, increases overall costs, and leads to the reduction of the lifetime of the membrane. Commonly used filtration materials such as polytetrafluorethylene (PTFE) and polyvinylidene fluoride (PVDF) are porous throughout and have a textured surface that facilitates the adhesion of bacteria and other foulants. To prevent this adhesion, bioinspired liquid-coated filters are proposed as a new approach to creating filters that resist fouling. Liquid-coated filters were created by immobilizing a water-immiscible liquid on the surface of commercially available synthetic filters. For water filtration tests, 0.45 μm pore diameter PTFE and PVDF filters were coated with omniphobic perfluoropolyether (PFPE) liquids. The continuity of the surface liquid layer was measured by testing how easily a water droplet could begin to move on the surface. The results indicate that infused PTFE membranes form a superhydrophobic surface with a sliding angle of approximately 5ᵒ, 75% lower than the infused PVDF. The ability of the infused membranes to resist biofilm formation was measured by incubating in growth media with Staphylococcus epidermidis for 24 hours. Infused PVDF membranes reduced biofilm formation by approximately 25% compared to bare controls while infused PTFE membranes reduced biofilm formation by approximately 98%. Pure water permeability (PWP) experiments conducted at an applied pressure of 1.5 bar indicated that liquid-coated PVDF membranes had a statistically equivalent PWP of 2827 ± 323 L/m2-h-bar, for over 10 cycles of use, showing that the immobilized liquid is present and stable within the pores. For aerosol filtration materials, new solid-liquid pairings were investigated. HEPA filters were infused with PFPE and evaluated for their ability to resist crystal violet staining and the changes in filtration efficiency. Infused HEPA filters showed an increased ability to resist crystal violet staining, but a lowered filtration efficiency. The fouling resistance of the infused HEPA filters suggest that sample viability after recovery could be increased and that these filtration materials could be applied to an air sampling system for public health monitoring. Based on the positive results of both liquid-coated PVDF and HEPA filters in functional applications despite poor results in surface characterization, we’ve begun exploring how to create more sustainable liquid-coated filters. Paper filters were coated with a thin layer of polydimethylsiloxane (PDMS) via chemical vapor deposition. These PDMS-coated paper filters were then infused with silicone oil. These new liquid-coated paper filters will be characterized based on surface properties and for functionality with aerosol and liquid filtration. The use of liquid-coated materials in water and air purification applications opens new doors for the creation of filtration materials that resist the adhesion of contaminants and resist fouling.

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