Department of Chemical Engineering Graduate Theses

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    Ionic Liquids as Electrolytes for Reduced Graphene Oxide Based Supercapacitors
    Hawrylow, Matthew J.; Chemical Engineering; Parent, Scott; Barz, Dominik
    Supercapacitors comprised of graphene hydrogel electrodes and ionic liquid electrolytes are prepared and characterized in terms of material properties and device performance. Thermal reduction of aqueous graphene oxide dispersions yields poroelastic hydrogels with the surface area required of an electric double layer capacitor (EDLC), while the use of imidazolium tetrafluoroborate ionic liquid (IL) provides much wider electrochemical stability window than conventional aqueous based electrolytes. The study focuses on the influence of a poly(ionic liquid) (PIL) on the properties of an IL electrolyte as well as the performance of an EDLC device. Of particular interest is the relationship between the viscosity and the ionic conductivity of an IL electrolyte. In general, those ILs that provide high ion conductivity have low fluid viscosity, which can complicate the design of flexible EDLCs. However, small amounts of a high molecular weight PIL are shown to affect IL viscosity disproportionately over ionic conductivity. Adding 5 wt% of poly(vinyl butyl imidazolium) tetrafluoroborate to 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4) increases the IL viscosity by 328% at the expense of only a 20% decline in conductivity. The higher viscosity provided by a PIL+ IL solution alters the stress response of a hydrogel when it is subjected to compression, as it provides increased resistance to flow of electrolyte from hydrogel pores. In addition, the more viscous medium provides better elastic recovery when a hydrogel is subjected to repeated compression. The addition of PIL to the electrolyte of a graphene-based hydrogel supercapacitor results in a 20% decrease in capacitance, due to ionic conductivity losses. As such, EDLC design requires optimization of capacitance at the expense of mechanical robustness. Compression of a flexible supercapacitor increases performance by reducing equivalent series resistance, giving a maximum capacitance of 133 F/g at 1A/g and 62.5% strain. However, at 87.5% strain densification of the hydrogel leads to a reduction in effective surface area and an 18% decrease in capacitance.
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    Non-Covalent Modification of Cellulose Nanocrystals with Block Copolymers
    Torres Rocha, Olga L.; Chemical Engineering; Cunningham, Michael; Champagne, Pascale
    Crystalline nanocellulose (CNC) exhibits extraordinary properties, and it can improve properties of a host material when used as reinforcing agent. Because of this, industrial and academic researchers have focused their efforts on the development of CNC-based products. However, CNC faces a major challenge that prevents the broader development of CNC-based products, which is its poor compatibility with non-polar (or hydrophobic) systems. CNC surface modification with polymer chains or small molecules helps to improve its compatibility, although these approaches often are complex and considered too expensive to be adopted by industry. In this dissertation, CNC surface was non-covalently modified with block copolymers with the primary objective of making CNC more compatible with less polar environments. Five new block copolymers (composed of an anchor and a stabilizing block) were synthesized via nitroxide-mediated polymerization. The block copolymers investigated were (poly(styrene)-b-poly(butyl vinyl imidazolium bromide), poly(n-butyl acrylate)-b-poly(butyl vinyl imidazolium bromide), poly(hexyl acrylate)-b-poly(butyl vinyl imidazolium bromide), poly(polyethylene glycol methacrylate)-b-poly(butyl vinyl imidazolium bromide) and (poly(lauryl methacrylate)-b-poly(butyl vinyl imidazolium bromide). Dispersibility of the modified CNC in less polar systems (organic solvents) was evaluated. The effect of the degree of polymerization of each block and their nature on the dispersion of the new polymer CNC based materials was examined. It was found that the degree of polymerization of both the anchoring and the stabilizing blocks have a significant impact on the amount of the polymer that can be bound to the CNC surface and in the dispersion of the new CNC based materials. The results obtained demonstrate that with this new approach, CNC surface properties can be effectively and simply modified, potentially leading to the development of CNC materials for industrial applications.
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    Impact of vitronectin adsorption on macrophage mediated degradation of poly(trimethylene carbonate)
    MacMillan, Owen D.; Chemical Engineering; Amsden, Brian
    Macrophages are known to exhibit different responses when cultured on different materials. This phenomenon is hypothesized to be directly related to the composition and configuration of the layer of adsorbed proteins on the material’s surface that forms following exposure to proteincontaining medium (i.e., blood, plasma, serum, etc.). However, the impact of specific proteins on unstimulated macrophage behaviour is an area of research in which little is known. Relative differences in quantity of specific adsorbed proteins has previously been shown to exist between poly(trimethylene carbonate) (PTMC) and crosslinked, acrylated star poly(D,L-lactide-co-ϵ-caprolactone) (ELAS) with similar mechanical properties. Further, PTMC and ELAS have been shown to undergo different degradation behaviour in the presence of macrophages, with PTMC degrading and ELAS resisting macrophage mediated surface erosion. Vitronectin, an integrinbinding glycoprotein present in plasma, has been found to be associated with monocyte/macrophage attachment, proliferation, interleukin-4 (IL-4) induced macrophage FBGC formation, and adsorb to ELAS in relatively higher quantities vs. PTMC. This work investigates the impact of PTMC surfaces pre-adsorbed with vitronectin on subsequent macrophage behaviour. Cell number, production of reactive oxygen species (ROS), and enzymatic activity were measured for macrophages cultured on PTMC and ELAS. Vitronectin-adsorbed PTMC (VN-PTMC) and ELAS samples exhibited similar properties at early time points with significantly decreased cell number and significantly increased enzymatic activity compared to non-adsorbed PTMC. Interestingly, all significance in the secretion of degradative species disappeared by day 7 of the 14-day degradation study. It is proposed that the macrophage’s diminishing enzymatic activity was due to a change in the adsorbed protein layer via competitive protein adsorption replacing or altering the conformation of adsorbed proteins, or by the degradation of the initially adsorbed protein layer corresponding to the vitronectin-signalled increase in enzymatic activity. This work provides insight into the impact of adsorbed vitronectin on macrophage behaviour, polymer degradation, and is a first look into the response of unstimulated macrophages to specific proteins.
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    A Second Order Extremum Seeking Controller with a Nonlinear Gain
    Battista, Angela S.; Chemical Engineering; Guay, Martin
    Extremum seeking control is an established model free optimization technique that estimates unknown system parameters and applies a gradient descent. Extremum seeking has proven to be a resourceful tool to effectively deal with systems with complex dynamics, where developing a model offline might be a challenging task. In this thesis, we apply extremum seeking control to two optimization problems. First, we develop a continuous time distributed extremum seeking controller with a nonlinear gain term which adapts to the system dynamics to ensure the controller gain is sufficiently large. The distributed controller has three main parts: 1) consensus, 2) parameter estimation and 3) extremum seeking control law with a nonlinear gain. The consensus algorithm provides each agent with an estimate of the average total cost of the system. From the consensus estimation, each agent performs its own parameter estimation routine to estimate the gradient of the average total cost and a system drift term. Finally, a Proportional-Integral extremum seeking control law is proposed using the gradient information provided by the parameter estimation routine. In the second part of this thesis, we develop an extremum seeking control law for a class of second order nonlinear systems. We propose a control law with a proportional, integral, and derivative term and a nonlinear gain term. We use a nested parameter estimation routine to estimate the gradient of the local cost function and a low power high gain observer to estimate the derivative of the gradient. We show that, under some assumptions, tuning parameters exist such that the system will converge to a region around the optimum.
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    Visible Light Stimulated Degradable Drug Release Devices for Ocular Delivery
    Qi, Ronghui; Chemical Engineering; Amsden, Brian
    Delivery of therapeutics including biopharmaceuticals and corticosteroids to ocular tissue has been a challenge due to the complex anatomy of the eye. There is a need to develop novel ophthalmic drug delivery systems to provide a prolonged therapeutic level of drugs and enhance bioavailability. Photoresponsive delivery systems provide spatiotemporal control of their properties in a non-invasive way, which may improve efficacy and reduce drug side effects when compared to existing approaches. In this work, visible-light degradable polymers were designed and investigated for their potential for the preparation of ocular delivery devices. The designed visible-light degradable polymer was derived from poly(5-hydroxytrimethylene carbonate) (PHTMC). The pendant hydroxyl groups of the PHTMC were protected by visible light-labile [7-(diethylamino)coumarin-4-yl]methyl (DEACM). Upon photo-irradiation, the DEACM group is removed, leaving PHTMC which degrades rapidly via intramolecular cyclization. In this work, a visible-light stimulated degradable hydrogel system and a micelle system based on DEACM protected PHTMC were created to provide sustained and controlled drug delivery. The hydrogel system was designed for intravitreal delivery of neurotrophic factors. The hydrogel is capable of providing sustained release of highly bioactive protein with a minimal burst effect and is ultimately degradable when triggered by visible light. The hydrogels exhibited a photo-triggered degradation profile. Hydrogels formed with 4a-PEG-thiol-5k provide sustained release of bioactive cytochrome as a model protein drug for 7 weeks with a minimal burst effect. A photo-responsive release profile was achieved by triggering hydrogel degradation, which altered the drug release rate on demand. A photo-degradable micelle formulation was designed for drug delivery, whose release profile can be remotely controlled by visible light irradiation to enable on-demand delivery. The micelle system was formed by a polycarbonate-based amphiphilic diblock copolymer, whose hydrophobic block was based on DEACM protected PHTMC. Upon the removal of these protecting groups by photo-irradiation, the micelles undergo structural disruption, leading to the release of the payload. The removal of DEACM would also deprotect the pendant hydroxyl groups of PHTMC, leading to PHTMC backbone degradation via iii intramolecular cyclization. To demonstrate proof-of-principle, the release of Nile Red and dexamethasone was examined. These approaches represent the first design as ocular delivery devices and have demonstrated great potential. While further improvements may be needed to enhance certain features, the preliminary assessments have been promising.