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Electrically conductive membranes (ECMs) are of significant research interest for their ability to mitigate fouling, enhance separation capacity, and induce electrochemical degradation of contaminants. Most ECM development has been in flat sheet format suitable for laboratory studies; in industrial applications, formats such as hollow fiber (HF) are preferred for their high packing density. While ECMs in HF format are emerging in research, these techniques typically employ the same methods proven for flat sheet, often involving direct deposition of conductive material onto a support membrane with no further investigation into how the deposition process affects ECM properties. This is a significant challenge for long (~1 m) HF membranes where coating uniformity is essential to ensure consistent performance. The goal of this project was to fabricate conductive HF membranes, ensuring uniform performance along the fiber. In this work, we have developed a “crossflow deposition” technique to deposit a uniform layer of single walled/ double walled carbon nanotubes (SW/DWCNTs) onto the interior surface of commercial polyether sulfone HF membranes. In a design-of-experiments model, feed pressure and crossflow velocity were shown to directly impact composite membrane conductivity and permeability. The highest permeability (~2900 LMH/bar) and conductivity (~670 S/m) were both achieved at the high pressure (0.2 bar) and high crossflow velocity (1.06 cm/s) condition. An inverse relationship was identified between conductivity and permeability for 29 different HF membranes coated under various flow and particle loading conditions. Similar trends were evident in ECM literature when comparing 80 membranes across 38 papers, covering various conductive materials, separation types, configurations, and applications. Metallic-based ECMs outperformed graphitic nanomaterial or conductive polymer-based ECMs with conductivities three orders of magnitude higher. This review also revealed a wide variation in performance testing with 35 unique pollutants in 63 total tests, indicating a need for standardization to accurately compare ECMs and a need for testing with more realistic feed sources. Finally, electrochemical degradation of methyl orange using the CNT-coated HF membranes was evaluated in batch and continuous removal experiments. Although no significant MO removal was detected in either configuration, these modules can be used for further optimization in terms of targeted conductivity, contact time, and electrochemical parameters such as applied voltage. This work highlights the existence of a conductivity/ permeability trade-off in ECM development and how manipulation of flow parameters during deposition can impact this trade-off in HF membrane development. / Thesis / Master of Applied Science (MASc) / Membrane separation technologies are a common purification strategy in many fields due to their simplicity and low energy requirements. Membranes operate by rejecting particles from feed water based on their chemical or physical properties such as size or charge. Long-term membrane operations are limited by fouling, incurring large operating costs for frequent cleaning cycles and downtime. Furthermore, traditional membrane separations only physically remove particles, presenting a risk for contaminant re-introduction into the environment. Electrically conductive membranes are an emerging strategy for addressing these concerns due to their demonstrated antifouling, enhanced selectivity, and redox capabilities. To date, these membranes have almost exclusively been developed as flat sheets with limited research into other membrane formats. Hollow fiber membranes resemble thin tubes ~1 mm in diameter and up to ~1 m in length where filtration occurs through the tubular wall of the fiber; the small diameter allows for hundreds of fibers to pack into an individual module, thus maximizing throughput. In this thesis, several issues with hollow fiber conductive membrane fabrication are addressed to ensure consistent performance along the length of the fiber. A key trade-off between membrane surface conductivity and throughput was found to exist universally in the conductive membrane field. This knowledge can be used to select fabrication methods and parameters to target certain performance ranges.

Climate change, water stress, and rapid population growth have increased the need to manage water resources through innovative sustainable technologies. Decentralized systems such as membrane treatment trains have become increasingly important to provide high volumes of potable water to millions of people. Pressure-driven membrane systems have dominated separation processes due to their low cost, small footprint, ease of operation, and high permeate quality. Conventionally, pressure-driven membranes are classified into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). MF and UF membranes operate under low pressure (< 7 bar, <~100 psi). They can separate a variety of large particles such as bacteria, natural organic matter, suspended solids, and colloids. In contrast, NF and RO membranes are more energy-intense due to operating at high pressures (7 – 80 bar, ~100 – 1200 psi) and can remove small molecules such as ions, pharmaceuticals, and heavy metals. Fouling is a primary challenge with membranes that compromises the membrane performance, increases energy consumption, and reduces the membrane lifetime. Many strategies are used to address fouling, such as pre-treatment (pH adjustment, screening, coagulation), membrane modification (chemical and morphological properties), and membrane cleaning (physical, chemical). However, such strategies increase operational expenditures, produce waste products that can impact the environment, and negatively impact membrane lifetimes. Recently, electrically conductive membranes (ECMs) have been introduced to address the challenges with traditional membranes. They contain conductive surfaces that offer self-cleaning and antifouling properties across the surface in response to electrical potential externally applied to them. ECMs are advantageous as compared to traditional membranes because (a) they are more effective in treating foulants as they target foulants at the membrane/solvent interface, (b) they are more economical and environmentally friendly as they reduce the need for chemical consumption, and (c) they can be responsive to fouling conditions as their antifouling mechanisms can be easily manipulated by changing the applied current type (positive, negative, direct current, alternating current) to match the foulant. ECMs have been formed from all categories of membranes (MF, UF, NF, MD, FO, and RO) with a range of applications. Despite the remarkable progress in demonstrating their excellent antifouling performance, there are many hurdles to overcome before they can be commercialized. Two of these are (a) a fundamental understanding of their underlying mechanisms, (b) surface materials that can withstand extreme chemical and electrical conditions. In this work, we have comprehensively discussed antifouling mechanisms with respect to surface polarization and elaborated on the impact of electrically-induced mechanisms on four major fouling categories. i.e., biofouling, organic fouling, mineral scaling, and oil wetting. In addition, we characterized surface properties of a common electrically conductive composite membrane composed of carbon nanotubes (CNTs) and polyvinyl alcohol (PVA). We then investigated the impact of cross-linkers in CNT/PVA network on transmembrane flux, electrical conductivity, hydrophilicity, and surface roughness. In addition, we proposed standard, practical, and straightforward methodologies to detect and quantify the electrochemical, physical, and mechanical stability of ECMs, using chronoamperometry and cyclic voltammetry, an evaluation of polymer leaching from membranes, and micro mechanical scratch testing, respectively. Our methods can readily be extended to all membrane-based separation processes and different membrane materials (carbonaceous materials, ceramics, metal-based, and polymers). To demonstrate the antifouling properties of ECMs, we challenged ECMs with mixed-bacterial cultures in a flow-through system. Although ECMs showed high rejection, comparable flux, and excellent self-cleaning performance under application of electrical potential, understanding the relationship between applied electrical currents and antifouling mechanisms demands a well-controlled investigation. To this end, we quantified the impact of electrochemically-induced acidic conditions, alkaline conditions, and H2O2 concentration on model bacteria, Escherichia Coli. We first quantified the electrochemical potential of CNT-based ECMs in generating stressors such as protons, hydroxyl ions, and H2O2, under a range of applied electrical currents (± 0-150 mA). Next, these individual stressors with identical magnitude were imposed on E. Coli cells and biofilms in batch and flow-through systems, respectively. This thesis guides researchers to understand the underlying antifouling mechanisms associated with ECMs, how to match the mechanisms to the application of ECMs, and offers benchmarks for making practical ECMs. / Thesis / Doctor of Philosophy (PhD)

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With the increasing demand for high performance communication networks and the proliferation of mobile devices, significant advances in antenna design are essential. In recent years the rising demands of the mobile wireless communication industry have forced antennas to have increased performance while being limited to an ever decreasing footprint. Such design constraints have forced antenna designers to consider frequency agile antennas so that their behavior can adapt with changing system requirements or environmental conditions. Frequency agile antennas used for mobile handset applications must also be inexpensive, robust, and make use of electronic switching with reasonable DC power consumption. Previous works have addressed a number of these requirements but relatively little work has been performed on frequency agile dielectric resonator antennas (DRAs). The objective of this thesis is to investigate the use of DRAs for frequency reconfigurability. DRAs are an attractive option due to their compactness, very low losses leading to high radiation efficiencies (better than 95%) and fairly wide bandwidths compared to alternatives. DRA’s are also well suited for mobile communications since they can be placed on a ground plane and are by nature low gain antennas whose radiation patterns typically resemble those of short electric or magnetic dipoles. One way to electronically reconfigure a DRA, in the sense of altering the frequency band over which the input reflection coefficient of the antenna is below some threshold, is to partially load one face of the DRA with a conducting surface. By altering the way in which this surface connects to the groundplane on which the DRA is mounted, the DRA can be reconfigured due to changes in its mode structure. This connection was first made using several conducting tabs which resulted in a tuning range of 69% while having poor cross polarization performance. In order to address the poor cross polarization performance a second conducting surface was placed on the opposing DRA wall. This technique significantly reduced the cross polarization levels while obtaining a tuning range of 83%. The dual-wall conductively loaded DRA was then extended to include a full electronic implementation using PIN diodes and varactor diodes in order to achieve discrete and continuous tuning respectively. The two techniques both achieved discrete tuning ranges of 95% while the varactor implementation also had a continuous tuning range of 59% while both maintaining an acceptable cross polarization level.

This dissertation explores the expansion of the Electrically Steerable Parasitic Array Radiator (ESPAR) technology to arrays using microstrip patch elements. Scanning arrays of two and three closely-coupled rectangular patch elements are presented, which incorporate no phase shifters. These arrays achieve directive radiation patterns and scanning of up to 26° with maintained impedance match. The scanning is effected by tunable reactive loads which are used to control the mutual coupling between the elements, as well as additional loads which compensate to maintain the appropriate resonant frequency. The design incorporates theoretical analysis of the system of coupled antennas with full-wave simulation. A prototype of the threeelement array at 1 GHz is fabricated and measured to exhibit a maximum gain of 7.4 dBi with an efficiency of 79.1%. Further, the microstrip ESPAR is thoroughly compared to uniformlyilluminated arrays of similar size. To satisfy the need for higher directivity antennas with inexpensive electronic scanning, the microstrip ESPAR is then integrated as a subarray. The three-element subcell fabrication is simplified to a single layer with an inverted-Y groove in the ground plane, allowing for DC biasing without the need for the radial biasing stubs or tuning stubs found in the two-layer design. The 1 GHz ESPAR array employs a corporate feed network consisting of a Wilkinson power divider with switchable delay line phase shifts, ring hybrid couplers, and achieves a gain of 12.1 dBi at boresight with ±20° scanning and low side lobes. This array successfully illustrates the cost savings associated with ESPAR subarray scanning and the associated reduction in required number of phase shifters in the RF front end.

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