Superabsorbent polymer (SAP) hydrogels function by absorbing and retaining water. Facile removal of the absorbed water would make it easier to recycle used SAP hydrogels. However, the hydrophilic interior of traditional SAP hydrogels inhibits the desorption of the absorbed fluid. Herein, we report the synthesis and properties of CO2-responsive SAP hydrogels capable of switching from being relatively hydrophobic to hydrophilic in the presence of CO2, and vice versa when the CO2 is removed, accompanied by the simultaneous absorption and expulsion of large volumes of water respectively, mimicking a CO2-directed sponge. The hydrogels studied are synthesized by the free-radical copolymerization of either N-[3-(dimethylamino)­propyl]­methacrylamide (DMAPMAm) or 2-N-morpholinoethyl methacrylate (MEMA) with N,N′-dimethylacrylamide (DMAAm), which acts as both a monomer and a self-cross-linker. In the presence of CO2, both p­(DMAAm-co-DMAPMAm) and p­(DMAAm-co-MEMA) gels were able to achieve a maximum swelling ratio (SR) of ∼800, demonstrating that they are superabsorbent. These gels release more than 70% of the absorbed water if they are immersed in noncarbonated water. Repeated swelling/deswelling of the hydrogels (with recovery of the original swelling ratio) in this manner over four cycles demonstrates the reusability of these materials and their potential use in a variety of applications.

This completion of this thesis owes a debt of gratitude to many individuals who have supported me through this arduous process. Many thanks are owed to Dr. Andrew Daugulis for his mentorship, guidance, availability and especially patience throughout this project. Personal thanks are owed to him for his commitment to making me a better scientist. Additional thanks are owed to him for helping me invoke my intrinsic curiosity and predilection for solving unanswered questions throughout the duration of this project. I would additionally like to thank all members of the staff at Queen's, who have made my work more enjoyable and aided in my understanding of graduate life. I would personally like to thank Dr. Ying Zhang for his friendship and technical expertise, without it I would still be stuck trying to fix our GC. I would also like to thank Rachel Vincent, my lab mate for making my time in the lab more enjoyable. I would like to thank my dad Robert Mullins for his support throughout this process. I would also like to thank my mom Mary-Beth Lester, for her unconditional support and keeping me optimistic throughout all my struggles and adjustments. I would also like to thank my grandparents Bill and Carol Lester for their ever-so curious attitude and general support regarding my research project, which is hard to find. I would also very much like to thank my girlfriend Katrina Kryza who moved 7 hours from home with me to support my dreams. Her enthusiasm and support for me throughout this 2-year project have helped me develop into a better person. She has never ceased to be my guiding star on the darkest of nights. vi

BACKGROUND: The water-intensive practice of hydraulic fracturing produces wastewater containing a variable matrix of organic and inorganic compounds, including ions and ionizable organic compounds. Extractive membrane bioreactors (EMBs) operating with tailored polymer membranes can selectively sequester and/or transport these solutes for biological treatment. Four grades of Hytrel™ tubing were compared for their suitability in EMB systems, based on the polymers' thermodynamic affinity for solutes and their ability to transport or speciate ionic wastewater constituents. RESULTS:Of the four Hytrel™ grades compared, high water content types (30% and 54% equilibrated water content) facilitated the transport of ionic species through the tubing, with all monovalent species being transported through both high-water content grades, and lack of transport through the low-water content tubing (3% and 5%). Undissociated organic acids were transported through all tubing types and dissociated acids were able to permeate only high-water content grades. Using this differential ability to transport/not transport an organic acid depending on its dissociation state, a low-water content Hytrel™ grade of tubing was able to concentrate a dilute butyric acid solution by 220% after 48 h. CONCLUSION: The use of polymeric tubing for EMB applications for the treatment of hydraulic fracturing wastewater requires knowledge of both solute affinity and water content for complex waste streams, both of which affect the capability to transport organic and ionic species.

There is a need to develop more accessible approaches to generate geologically realistic microheterogeneous structures in quasi‐two‐dimensional flow cells for use in light transmission experiments. In addition to automating the packing procedure to increase repeatability, such approaches would allow multiple researchers to investigate multiphase flow through similar heterogeneities across time and space. In this study, a three‐dimensional (3D) printer was modified to accommodate a sand‐filled hopper and used to create replicate packs that were similar to one another and to those produced in previous studies using a different apparatus. Replicate gas (CH4) injections were also used to assess the reproducibility of gas distributions in these replicate packs. Macroscopic features of the sand packs (bed height, number and location of laminae) and gas distributions (trapped gas volume, maximum gas width) were reproducible, but local‐scale features of the gas distribution (gas pathway, ganglia‐to‐pool ratio) were more variable.