Graduate Thesis Or Dissertation


Molecular Layer Deposition for Membrane Applications Public Deposited

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  • Molecular layer deposition (MLD) is a layer-by-layer technique capable of creating polymer thin films with monomer level control over thickness, cross-linking and chemical composition. With these capabilities, MLD is ideal the fabrication of polymeric membranes. Two crosslinked semipermeable polyamide MLD films, presented in Chapter 2, were made from m-phenylenediamine (MPD) and trimesoyl chloride (TMC) as well as piperazine and TMC. The growth and properties of the polyamides were characterized with FTIR, XPS and ellipsometry.Thin film composites were fabricated using MLD in Chapter 3. In this method, the pores of ultrafiltration membranes were capped with Al2O3 using plasma-enhanced atomic layer deposition. MPD-TMC MLD films were then deposited on the non-porous capping layer. The Al2O3 pore caps were then removed by timed backside exposures to a dilute sodium hydroxide solution. Pore-capping and etching was confirmed with gas permeance measurements. The removal of the Al2O3 pore caps on polymer substrates led to the detachment of the MLD film. However, the film was anchored to the support at fractures located in the Al2O3 film prior to the MLD. Anchoring was controlled by tuning the fracture density which was varied with applied tensile stress via sample bending. In the final chapter, a new nonporous support was utilized to produce reverse osmosis membranes with MLD. MPD-TMC films as thin as 0.5 nm were applied to NF270 nanofiltration membranes. Within two molecular layers, desalination performance was affected. As film thickness increased to 15 nm (48 MLD cycles), performance progressed from nanofiltration to reverse osmosis metrics in terms of salt rejection and water permeance. With film thickness >5 nm, rejection values exceeded a small sampling of commercial membranes. In all cases, a tradeoff between rejection and permeance was observed. Atomic force microscopy measurements indicate that MLD enhancement led to removal of small-scale roughness features and resulted in a root mean square roughness difference of <0.1 nm from the substrate. These initial MLD studies represent a novel processing approach that offers a potential pathway for the fabrication of membranes with finely tailored properties.

Date Issued
  • 2021-11-18
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  • 2023-01-02
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