Browsing by Author "Verduzco, Rafael"
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Item 3D Covalent Organic Frameworks with Interpenetrated pcb Topology Based on 8-Connected Cubic Nodes(American Chemical Society, 2022) Shan, Zhen; Wu, Miaomiao; Zhu, Dongyang; Wu, Xiaowei; Zhang, Kan; Verduzco, Rafael; Zhang, GenThe connectivity of building units for 3D covalent organic frameworks (COFs) has long been primarily 4 and 6, which have severely curtailed the structural diversity of 3D COFs. Here we demonstrate the successful design and synthesis of a porphyrin based, 8-connected building block with cubic configuration, which could be further reticulated into an unprecedented interpenetrated pcb topology by imine condensation with linear amine monomers. This study presents the first case of high-connectivity building units bearing 8-connected cubic nodes, thus greatly enriching the topological possibilities of 3D COFs.Item A Comprehensive Investigation of Polymer Binder Properties in Silicon Anodes for Lithium-Ion Batteries(2019-04-18) Miranda, Andrea; Verduzco, RafaelEnergy storage technologies with increased energy densities and lifetimes are needed for the advancement of electric and hybrid electric vehicles and storage of intermittent renewable energy, among other technologies with significant energy needs. High capacity anode materials that can alloy with lithium, such as silicon, hold great promise towards advancing the energy density of lithium-ion batteries, a major component of the energy storage sector. However, silicon anodes undergo catastrophic volumetric expansion as lithium ions react with silicon in the anode resulting in silicon particle fracture, delamination, and disruption of the electrical network in the electrode during cycling, eventually resulting in failure. One method to address failure of silicon anodes is through the development of novel polymeric binders, which can mitigate or prevent damage during cycling by suppressing cracking, adhering strongly to silicon and copper, and passivating the silicon anode surface. In this thesis, we explore the design, development, and characterization of novel polymeric binder materials for silicon anodes, in particular connecting physical properties of polymeric binders to specific design principles. In the first chapter, we review the development of novel polymeric binders with an emphasis on guiding design principles and characterization techniques. In the second chapter, we study a molecular weight series of high-modulus and high adhesion partially hydrolyzed polyacrylamide (HPAM) binders. Model and composite electrodes prepared with varying molecular weight of the polymer binder are analyzed to correlate physical properties to electrochemical behavior trends and failure modes of the binders. We attribute capacity decay in these materials due to poor lithium ion mobility, eventually leading to fraction and isolation of silicon. In another chapter, a series of conductive PEDOT:PSS conjugated polymer binders are crosslinked using three different chemistries and characterized with respect to mechanical properties, adhesion, electrochemical stability, cycling capacity and stability. Crosslinking is found to enhance performance, and poor cycling stability is attributed to poor adhesion to silicon and copper. This work systematically investigates and quantifies the physical properties of polymeric binders relevant to electrode stability and performance.Item Acetylene Functionalized Photocatalytic COFs for PFAS Adsorption and Degradation(2023-04-21) Tong, Xinbo; Verduzco, RafaelCovalent organic frameworks (COFs) are of deep interest in various applications due to their highly tunable architectures and porosities. COFs used as photocatalysts have great potential because they usually possess high surface areas for adsorption, tunable pore and surface functionalities, and various opto-electrical properties determined by the functional groups of building blocks. However, few examples of COFs have been successful in dealing with per- and polyfluoroalkyl substances (PFAS) due to the strong binding between fluorine and carbon atoms. The challenge is designing COFs that include electron-rich rings with a suitable pore size to absorb and degrade the contaminants. Herein, we demonstrate the novel synthesis of a series of COFs or amorphous porous organic polymers (APOP) with delocalized π-conjugated systems, followed by characterization and applications. First, we select a few monomers that contain electron-rich structures, such as pyrene and porphyrin groups, as predicted by band gap energy calculations. We then intentionally choose monomers with C-C triple bonds to combine and explore various solvent and reacting conditions. After the optimized conditions and reactants to form crystalline porous polymers have been found, we synthesize four different COFs and confirm their chemical structures and optical properties by characterizations. Finally, we explore the application of using these COFs as photocatalysts to absorb and photodegrade Perfluorooctanoic Acid (PFOA). Photodegradation experiment results indicate that the Porphyrin-COF has the highest efficiency for PFOA adsorption and degradation, with over 80% PFOA adsorbed and degraded within 3 hours of irradiation.Item Advanced Applications of Polymers for Enhanced Oil Recovery(2014-11-06) ShamsiJazeyi, Hadi; Hirasaki, George J; Verduzco, Rafael; Tour, James; Biswal, LisaWith the increasing global demand for crude oil, it is essential to increase the oil production in economic ways. This requires a significant increase in application of advanced technologies in this area. Enhanced Oil Recovery (EOR) processes are known as series of different advanced technologies, which can be used to increase the oil production from a given oil reservoir. The traditional use of polymers in EOR is almost limited to increasing viscosity of the aqueous fluids injected into the reservoir. By increasing the viscosity of the injected fluids, more areas of the reservoir can be swept, and therefore more oil is expected to be recovered. In this thesis proposal, a number of advanced polymer applications for EOR are investigated. Polymers are known as a very promising class of materials with wide range of properties, especially combined with other advanced materials, such as nanoparticles. Therefore, there is a huge potential for developing new application of polymers in EOR processes. The first application introduced in this thesis is to use polymers as sacrificial adsorption agents for anionic surfactants. In a subclass of EOR, known as chemical EOR, surfactants are injected to lower the interfacial tension of oil and brine, resulting in recovery of more oil. However, one of the challenges facing these processes is the adsorption of surfactants onto the reservoir rock, which requires excessive injection of surfactant to compensate for the adsorption. This significantly increases the cost of the chemical EOR to values much more than what is actually needed for oil recovery. In second chapter of this thesis, sodium polyacrylate is introduced as a sacrificial adsorption agent, a chemical that is injected to decrease the adsorption of anionic surfactant. The results show that the material cost of chemical EOR can be reduced by up to 80% in case of using polyacrylate as a sacrificial agent for anionic surfactants. In addition, application of polyacrylate as a sacrificial agent for zwitterionic surfactants was investigated. In spite the significant reduction seen in the adsorption of anionic surfactants once polyacrylate is used, adsorption of zwitterionic surfactants is only slightly reduced after adding polyacrylate. In order to understand the reasons behind this dismal reduction, the effect of pH on adsorption of lauryl betaine (as the zwitterionic surfactant in this study) is studied. Based on the experimental data, a hypothetic mechanism is introduced to explain the adsorption properties of betaine. This hypothetic mechanism also explains why polyacrylate shows a very slight reduction in adsorption of zwitterionic surfactants while it significantly reduces adsorption of anionic surfactants. Finally, the effect of polymer coating on interfacial properties of nanoparticles in the absence or presence of surfactants is studied. Interfacial properties of polymer-coated nanoparticles in EOR have been traditionally limited to only emulsions (Pickering Emulsions). In this thesis, we have provided experimental evidence that polymer-coated nanoparticles can migrate to micro-emulsion phases even in the absence of emulsions. Some of these polymer-coated nanoparticles are dispersed in aqueous solutions, but they will precipitate in the micro-emulsion phase once mixed with the oil. This observation by itself can be used in EOR applications through understanding the fact that aqueous stability of nanoparticles is not the sufficient condition for nanoparticles to remain stable when injected into oil reservoirs. Many previous researchers have only focused on stability of nanoparticles in aqueous solutions as the only requirement for stability of nanoparticles even after injection into oil reservoir. This assumption is challenged based on our work in this thesis.Item Advanced Synthesis Techniques and Characterization of Functional Semiconductor Nanomaterials(2014-01-15) Gullapalli, Sravani; Wong, Michael S.; Verduzco, Rafael; Ajayan, Pulickel M.Semiconductor materials are used in several modern day applications ranging from photovoltaic devices to environmental remediation. The electronic, optical, catalytic and physical properties of semiconductor nanomaterials can be precisely tuned by altering their size, shape and composition. It is thus imperative to develop simplified cost-effective techniques to synthesize functional semiconductor nanomaterials with structural and morphological control. The overall goal of this thesis is to design new synthetic schemes for well-characterized semiconductor nanomaterials and subsequently demonstrate their potential in photovoltaic and photocatalytic applications. Shape control of semiconductor nanomaterials is crucial for photovoltaic applications. Longer armed cadmium selenide (CdSe) tetrapods have demonstrated enhanced performance in hybrid solar cells. Conventional long arm tetrapod syntheses necessitate multiple injections of flammable phosphorous based chemicals. A new non-phosphorous route to long CdSe tetrapods with arm lengths > 70 nm is demonstrated by manipulating the “greener” selenium precursor temperature in the presence of a quaternary ammonium salt as the shape directing agent. Another interesting shape is the hollow morphology that provides the advantage of higher surface-to-volume ratio. However this shape for CdSe is much less investigated in photovoltaic applications. A novel molten-droplet synthesis strategy is developed to synthesize quantum confined CdSe HNPs based on the slow heating of a low melting point cadmium salt, elemental Se, alkylammonium surfactant in octadecene solvent with no external ligand. This generic technique is shown to be applicable for a variety of metal chalcogenide compositions. Further, photovoltaic device characterization of HNPs in a hybrid solar cell indicate that HNPs have improved electron transport characteristics compared to standard CdSe quantum dots. Hybrid photovoltaic device fabrication is based on low cost colloidal solution-based techniques. A new insight to understanding nanoparticle solvent interactions is provided using coarse-grained computational models and experimental characterization of oleate-capped NPs in various solvents. Solvent polarity was shown to strongly affect NP hydrodynamic diameter, colloidal stability and aggregation behavior. Photocatalytic removal of organic contaminants using semiconductor nanomaterials provides a low-cost, environmentally clean alternative for the utilization of renewable energy sources. Most photocatalytic environmental remediation techniques are oxidative and result in either partial or complete mineralization of the contaminant. A less explored reductive photocatalytic approach to organohalide removal has been demonstrated without necessitating an external co-feed of hydrogen (H2). Hydrodechlorination (HDC) of trichloroethene (TCE) as the test reaction. Bifunctional palladium-based titanium dioxide (TiO2) reduction catalysts were synthesized for the photocatalytic TCE HDC reaction with simultaneous in-situ H2 generation by photocatalytic water splitting. Extension of this reductive photocatalytic approach to other groundwater contaminants could simplify future remediation efforts.Item Embargo Advancing Precision and Controllable Molecular Tools for Genetic Engineering and Disease Treatment(2024-04-17) Zeng, Hongzhi; Gao, Xue; Verduzco, RafaelThe emergence of programmable gene editing tools has transformed life sciences by empowering researchers to execute precise and targeted genomic alterations in living cells. The advent of the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (CRISPR-Cas) technology has greatly accelerated genome editing research and applications. However, CRISPR-Cas faces limitations due to the low efficiency of homology-directed repair after Cas nuclease- induced double-stranded DNA breaks (DSBs), which can result in unintended genomic alterations and raise safety concerns. Base editors (BEs), leveraging a catalytically impaired nuclease and a single-stranded DNA deaminase enzyme, offer a promising alternative by facilitating targeted point mutations without requiring DSBs or donor DNA templates. However, the challenge of off-target effects and the lack of temporal control over BE activity when delivered via viral vectors remain significant hurdles. My thesis describes two projects that I lead: (1) A split and inducible adenine base editor for precise in vivo base editing, and (2) Precision A3G base editors and prime editors for cystic fibrosis modeling and correction. These projects explore the underlying principles of BEs, detailing engineering strategies for achieving small-molecule-controlled base editing in vivo and outline efforts to enhance the specificity of adenine and cytosine base editors. Additionally, these projects involve viral and non-viral delivery methods for BEs, emphasizing their applications in human disease modeling, treatment, and prevention. Lastly, my projects contain applications of prime editing technology, a more versatile gene-editing tool than BE, highlighting its promise for biological research and therapeutic applications.Item All-Conjugated Block Copolymers for Organic Photovoltaic Applications(2014-12-03) Smith, Kendall Allen; Verduzco, Rafael; Chapman, Walter G; Hartgerink, Jeffrey DConventional inorganic solar technologies are expensive due to the high cost of processing, while organic materials have significant cost advantages in the raw materials and ease of processing. Unfortunately, organic devices suffer from low efficiency due to difficulty in transporting charges to the electrodes. Typical devices mix the donor and acceptor components and anneal them to allow for phase separation. However, because the phase separation is uncontrolled, domains may be larger than optimal and isolated domains can be formed reducing efficiency. All-conjugated block copolymers have the potential to improve efficiency by creating an ordered structure with controlled domains and continuous pathways through self-assembly. In this work, the relationships between structure, optoelectronic properties, and processing conditions for these materials are systematically investigated using two routes to obtain the materials. In one route, functionalized catalysts are used to initiate controlled polymerizations of two different polymers. These well functionalized precursors are then joined together using copper catalyzed azide alkyne click chemistry. In a second route, a sequential polymerization route is employed where one polymer is synthesized with a well-defined end-group. The polymer is then used as a macroreagent to end-cap a Suzuki polycondensation reaction, yielding materials with direct conjugation between the blocks. The first route yields well-defined materials, whereas the second can access a broader variety of polymers. For all these materials, processing conditions are varied and the morphology of the all-conjugated block copolymers are analyzed by a combination of grazing-incidence X-ray scattering, neutron scattering and reflectivity, atomic force microscopy, and transmission electron microscopy. Materials are found to self-assemble into thermodynamically stable structures with well-defined length scales. It is found that crystallization of either block is predominant in all block copolymers studied, but at intermediate ratios crystallization of both blocks is observed. Processing conditions such as casting temperature, annealing duration, and speed of quenching to room temperature are found to have important effects on thin film crystallinity and orientation of the π-π stacking direction of polymer crystallites. By varying the annealing duration and quenching speed, crystallization of either or both block can be obtained.Item All-Conjugated Block Copolymers for Organic Photovoltaics(2015-04-20) Lin, Yen-Hao; Verduzco, Rafael; Wong, Michael S; Barron, Andrew ROrganic photovoltaics (OPVs) are a promising source of alternative energy due to cost effectiveness and process simplicity. However, the performance of OPVs must be improved to produce viable devices. This can be achieved by optimizing the optoelectronic properties of constituent materials, tuning the nanostructures of materials within active layer of OPVs and defining a well-defined interface between electron-donor materials and electron-acceptor materials. The above opportunities can potentially be addressed with using all-conjugated block copolymers in that self-assembly of block copolymers can lead to well-defined nanostructures driven by thermodynamics. The focus of this thesis is on the synthesis and development of all-conjugated block copolymers in which one block is an electron-donor polymer and the other is an electron-acceptor polymer. We focus primarily on poly(3-hexylthiophene) (P3HT)-based block copolymers in which the electron-donor P3HT is made from Grignard metathesis polymerization (GRIM) and the other block is synthesized by Suzuki-Miyaura polycondensation reaction for wide variety of electron-acceptor polymers. Subsequently, the nanostructures of polymers were studied on a model series of all-conjugated block copolymer: poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene) (P3HT–b–PF) under different processing conditions with using differential scanning calorimetry (DSC) and grazing-incidence X-ray scattering (GIXS). This reveals strong process-structure-property relationships of all-conjugated block copolymers. Furthermore, using our two-step synthetic route, we prepared an all-conjugated block copolymer poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′,-benzothiadiazole)] (P3HT–b–PFTBT) that exhibits over 3% PCEs as the active layer in a solution processed OPV due to the formation of lamellae of the block copolymers and preferential π-π stacking direction of the P3HT perpendicular to the substrate. In addition to covalently linked block copolymers, we applied a quadruple hydrogen group, 2-ureido-4[1H]-pyrimidinone (UPy), as polymeric end functionalities to reduce macro-phase separation in polymer blends. In the polymer blends OPVs comprised of P3HT and PFTBT, the UPy hydrogen bonding group reduces macro-phase separation in polymer blends and leads to improved power conversion efficiency of OPVs from 0.43% to 0.77% under 155 oC annealing condition. This thesis demonstrates that both the covalently linked and hydrogen bonding linked all-conjugated block copolymers are potential to enhance performance of OPVs. Furthermore, with the advancement in synthetic techniques and better understandings on structure-processing-property relationships of all-conjugated block copolymers, we are able to apply those into more emerging conjugated polymers and engineer molecules for efficient energy generation in OPVs.Item Amphiphilic Bottlebrush Block Copolymers: Analysis of Aqueous Self-Assembly by Small-Angle Neutron Scattering and Surface Tension Measurements(American Chemical Society, 2019) Alaboalirat, Mohammed; Qi, Luqing; Arrington, Kyle J.; Qian, Shuo; Keum, Jong K.; Mei, Hao; Littrell, Kenneth C.; Sumpter, Bobby G.; Carrillo, Jan-Michael Y.; Verduzco, Rafael; Matson, John B.A systematic series of 16 amphiphilic bottlebrush block copolymers (BCPs) containing polystyrene and poly(N-acryloylmorpholine) (PACMO) side chains were prepared by a combination of atom-transfer radical polymerization (ATRP), photoiniferter polymerization, and ring-opening metathesis polymerization (ROMP). The grafting-through method used to prepare the polymers enabled a high degree of control over backbone and side-chain molar masses for each block. Surface tension measurements on the self-assembled amphiphilic bottlebrush BCPs in water revealed an ultralow critical micelle concentration (cmc), 1–2 orders of magnitude lower than linear BCP analogues on a molar basis, even for micelles with >90% PACMO content. Combined with coarse-grained molecular dynamics simulations, fitting of small-angle neutron scattering traces (SANS) allowed us to evaluate solution conformations for individual bottlebrush BCPs and micellar nanostructures for self-assembled macromolecules. Bottlebrush BCPs showed an increase in anisotropy with increasing PACMO content in toluene-d8, which is a good solvent for both blocks, reflecting an extended conformation for the PACMO block. SANS traces of bottlebrush BCPs assembled into micelles in D2O, a selective solvent for PACMO, were fitted to a core–shell–shell model, suggesting the presence of a partially hydrated inner shell. Results showed an average micelle diameter of 40 nm with combined shell diameters ranging from 16 to 18 nm. A general trend of increased stability of micelles (i.e., resistance to precipitation) was observed with increases in PACMO content. These results demonstrate the stability of bottlebrush polymer micelles, which self-assemble to form spherical micelles with ultralow (<70 nmol/L) cmc’s across a broad range of compositions.Item An experimental and computational study of donor–linker–acceptor block copolymers for organic photovoltaics(Wiley, 2018) Hu, Zhiqi; Jakowski, Jacek; Zheng, Chenyu; Collison, Christopher J.; Strzalka, Joseph; Sumpter, Bobby G.; Verduzco, RafaelBlock copolymers with donor and acceptor conjugated polymer blocks provide an approach to dictating the donor–accepter interfacial structure and understanding its relationship to charge separation and photovoltaic performance. We report the preparation of a series of donor‐linker‐acceptor block copolymers with poly(3‐hexylthiophene) (P3HT) donor blocks, poly((9,9‐dioctylfluorene)‐2,7‐diyl‐alt‐[4,7‐bis(thiophen‐5‐yl)‐2,1,3‐benzothiadiazole]‐2′,2″‐diyl) (PFTBT) acceptor blocks, and varying lengths of oligo‐ethylene glycol (OEG) chains as the linkers. Morphological analysis shows that the linkers increase polymer crystallinity while a combination of optical and photovoltaic measurements shows that the insertion of a flexible spacer reduces fluorescence quenching and photovoltaic efficiencies of solution processed photovoltaic devices. Density functional theory (DFT) simulations indicate that the linking groups reduce both charge separation and recombination rates, and block copolymers with flexible linkers will likely rotate to assume a nonplanar orientation, resulting in a significant loss of overlap at the donor–linker–acceptor interface. This work provides a systematic study of the role of linker length on the photovoltaic performance of donor–linker–acceptor block copolymers and indicates that linkers should be designed to control both the electronic properties and relative orientations of conjugated polymers at the interface.Item Analysis of Liquid Chemisorbent for CO2 removal and Solvent Vapor Processing of Ternary Polymer Blends(2018-04-20) Sharma, Saurabh; Verduzco, RafaelA robust, reliable, and low-power system is needed for carbon dioxide (CO2) remediation in deep-space exploration systems. The current CO2 removal system on the International Space Station relies on zeolites, but an alternative CO2 scrubbing technology based on liquid amines has recently been proposed and demonstrated. In this project, we critically evaluate the use of liquid amines to uptake CO2 and provide recommendations for implementation and optimization. We model CO2 uptake using COMSOL and generate concentration profiles for liquid amine and CO2 in gas and liquid phases. We show that liquid amines have significant capacity for CO2 uptake, and the rate of uptake is limited by the available surface area and CO2 diffusion in the gas phase. Higher surface areas, gas mixing, and increased gas velocities can produce uptake rates needed for CO2 removal. The second project focusses on solvent vapor processing of ternary polymer blends to produce co-continuous phases. Co-continuous phases are of interest for a broad range of applications including separations, energy storage, photovoltaics, among other applications. However, most methods for producing co-continuous phases rely on kinetically-arrested phase separation. Here, we pursue the development of equilibrium co-continuous phases through ternary polymer blends consisting of two homopolymers and a compatibilizing block copolymer. We specifically focus on solvent-vapor annealing to equilibrate blends and achieve co-continuous structures in polymer films. Our work shows that solvent-vapor annealing can be used to target and tailor the domain sizes of co-continuous polymer blend films.Item Aqueous-Processed, High-Capacity Electrodes for Membrane Capacitive Deionization(American Chemical Society, 2018) Jain, Amit; Kim, Jun; Owoseni, Oluwaseye M.; Weathers, Cierra; Caña, Daniel; Zuo, Kuichang; Walker, W. Shane; Li, Qilin; Verduzco, Rafael; NSF Nanosystems Engineering Research Center, Nanotechnology-Enabled Water TreatmentMembrane capacitive deionization (MCDI) is a low-cost technology for desalination. Typically, MCDI electrodes are fabricated using a slurry of nanoparticles in an organic solvent along with polyvinylidene fluoride (PVDF) polymeric binder. Recent studies of the environmental impact of CDI have pointed to the organic solvents used in the fabrication of CDI electrodes as key contributors to the overall environmental impact of the technology. Here, we report a scalable, aqueous processing approach to prepare MCDI electrodes using water-soluble polymer poly(vinyl alcohol) (PVA) as a binder and ion-exchange polymer. Electrodes are prepared by depositing aqueous slurry of activated carbon and PVA binder followed by coating with a thin layer of PVA-based cation- or anion-exchange polymer. When coated with ion-exchange layers, the PVA-bound electrodes exhibit salt adsorption capacities up to 14.4 mg/g and charge efficiencies up to 86.3%, higher than typically achieved for activated carbon electrodes with a hydrophobic polymer binder and ion-exchange membranes (5–13 mg/g). Furthermore, when paired with low-resistance commercial ion-exchange membranes, salt adsorption capacities exceed 18 mg/g. Our overall approach demonstrates a simple, environmentally friendly, cost-effective, and scalable method for the fabrication of high-capacity MCDI electrodes.Item Bottlebrush Copolymer Additives for Immiscible Polymer Blends(American Chemical Society, 2018) Mah, Adeline Huizhen; Afzali, Pantea; Qi, Luqing; Pesek, Stacy; Verduzco, Rafael; Stein, Gila E.Thin films of immiscible polymer blends will undergo phase separation into large domains, but this behavior can be suppressed with additives that accumulate and adhere at the polymer/polymer interface. Herein, we describe the phase behavior of polystyrene/poly(methyl methacrylate) (PS/PMMA) blends with 20 vol % of a bottlebrush additive, where the bottlebrush has poly(styrene-r-methyl methacrylate) side chains with 61 mol % styrene. All blends are cast into films and thermally annealed above the glass transition temperature. The phase-separated structures are measured as a function of time with atomic force microscopy and optical microscopy. We demonstrate that subtle changes in bottlebrush architecture and homopolymer chain lengths can have a large impact on phase behavior, domain coarsening, and domain continuity. The bottlebrush additives are miscible with PS under a broad range of conditions. However, these additives are only miscible with PMMA when the bottlebrush backbones are short or when the PMMA chains are similar in length to the bottlebrush side chains. Otherwise, the limited bottlebrush/PMMA miscibility drives the formation of a bottlebrush-rich interphase that encapsulates the PMMA-rich domains, stabilizing the blend against further coarsening at elevated temperatures. The encapsulated domains are aggregated in short chains or larger networks, depending on the blend composition. Interestingly, the network structures can provide continuity in the minor phases.Item Bottlebrush Polymers for Surface Modification(2020-12-03) Mei, Hao; Verduzco, RafaelBottlebrush polymer is a kind of macromolecule with dense side-chain densely grafted side-chains. Because of the steric force among the side-chains, bottlebrush polymer exhibits distinct behaviors. In addition, its complex structure offers additional dimensions to tailor bottlebrush polymer, which provides a platform to design bottlebrush polymer for different applications such as antifouling, drug delivery, photonic crystals. This dissertation focuses on applying bottlebrush polymers for surface modification. Surface property is crucial for material applications. For this dissertation, we propose two different approaches to modify the surface properties by either applying a bottlebrush polymer coating layer on the surface or blending bottlebrush polymer additives with bulk materials. For chapter two, we report that bottlebrush polymers with an unsaturated polynorbornene backbone and thiol-terminated side chains can be cross-linked on demand by UV irradiation to produce uniform and insoluble bottlebrush polymer coatings. By comparing a parameter as normalized residual thickness, we systematically study the influence of UV dose, side-chain length, backbone DP, different chemical composition and temperature. The cross-linking process outlined in this work is simple, general, and efficient and produces solvent-resistant coatings that preserve the unique properties and functions of bottlebrush polymers. For the next chapter, we discuss another surface modification approach as utilizing bottlebrush polymer additives. Bottlebrush copolymer with poly(methyl methacrylate) (PMMA) and polystyrene (PS) mixed arm side-chains (BBPS-m-PMMA) is blended with either linear PS or PMMA before and after thermal annealing. We find that the bottlebrush copolymers segregated to air and substrate interfaces above a critical molecular weight of the linear homopolymer, consistent with an entropic preference for chain ends and shorter chains toward the interfaces. This segregation is used to tailor the surface wettability of blend films using bottlebrush additives as a minority component. Chapter four investigates the influence of polymer architecture on its phase distribution behaviors. We synthesize two different bottlebrush polymers with similar chemical composition but different architectures, i.e. bottlebrush copolymer with either random side-chains (BBPS-r-PMMA) or mixed arm side-chains (BBPS-m-PMMA). After blending them with linear homopolymers, different phase behaviors are observed. It is due to the miscibility differences caused by the architecture variations. Next, another bottlebrush polymer, bottlebrush poly(cyclohexyl methacrylate) (BBPCHMA) with linear PS is studied. PS and PCHMA has attractive chemical interactions, indicating a preference of mixing for the two different components. We find the truly segregation of bottlebrush copolymer is not only affected by parameter and entropy effect, but also the surface energy, kinetical effects. Besides, the self-healing properties by the bottlebrush additives diffusion is demonstrated. In the sixth chapter, we study the chemical composition influence on bottlebrush polymer phase behaviors. Bottlebrush polymers with PS and polyethylene glycol (PEG) mixed arm side-chains (BBPS-m-PEG) are synthesized and blended with both PS linear polymers. Uniform phase can still be observed though the repulsive interaction between these two arms is relatively high. Entropy driven force overwhelms the preferences of lower surface energy composition at the interfaces and leads to the enrichment of additives with both compositions above a critical molecular weight of the linear homopolymer.Item Catalytic Organosilane Activation with Copper Complexes(2013-07-24) Herron, Jessica; Ball, Zachary T.; Tour, James M.; Verduzco, RafaelThe development of reactive organometallics has become a vital part synthetic chemistry. Organosilanes potentially represent a cheap, robust, and environmentally benign precursor to reactive organometallics, but the nature of the very stable C−Si bond has generally prevented their use as precursors to more reactive organometallics. We present investigations into copper fluoride complexes which activate organosilanes in anhydrous media under mild conditions, effecting transmetalation to produce stable and in some cases isolable organocopper species containing sensitive functional groups including carbonyl groups, aryl bromides, benzylic chlorides, and alkyl ketones. This discovery allows us to better understand the fundamental reactivity of presumed intermediates in copper-catalyzed reactions and to develop new catalytic bond-forming processes including allylations of aldehydes, 1,4-addition of vinyl epoxides, and intramolecular ring closures.Item Challenges in photocatalysis using covalent organic frameworks(IOP Publishing, 2024) Jiang, Shu-Yan; Senftle, Thomas P.; Verduzco, Rafael; NanoEnabled Water Treatment CenterPhotocatalysis is an attractive, energy-efficient technology for organic transformations, polymer synthesis, and degradation of environmental pollutants. There is a need for new photocatalysts stable in different media and that can be tailored for specific applications. Covalent organic frameworks (COF) are crystalline, nanoporous materials with π-conjugated backbone monomers, representing versatile platforms as heterogeneous, metal-free photocatalysts. The backbone structure can be tailored to achieve desired photocatalytic properties, side-chains can mediate adsorption, and the nanoporous structure provides large surface area for molecular adsorption. While these properties make COFs attractive as photocatalysts, several fundamental questions remain regarding mechanisms for different photocatalytic transformations, reactant transport into porous COF structures, and both structural and chemical stability in various environments. In this perspective, we provide a brief overview of COF photocatalysts and identify challenges that should be addressed in future research seeking to employ COFs as photocatalysts. We close with an outlook and perspective on future research directions in the area of COF photocatalysts.Item Characterization of polymeric surfaces and interfaces using time-of-flight secondary ion mass spectrometry(Wiley, 2022) Mei, Hao; Laws, Travis S.; Terlier, Tanguy; Verduzco, Rafael; Stein, Gila E.; Shared Equipment AuthorityTime-of-flight secondary ion mass spectrometry (ToF-SIMS) is used for chemical analysis of surfaces. ToF-SIMS is a powerful tool for polymer science because it detects a broad mass range with good mass resolution, thereby distinguishing between polymers that have similar elemental compositions and/or the same types of functional groups. Chemical labeling techniques that enhance contrast, such as deuterating or staining one constituent, are generally unnecessary. ToF-SIMS can generate both two-dimensional images and three-dimensional depth profiles, where each pixel in an image is associated with a complete mass spectrum. This Review begins by introducing the principles of ToF-SIMS measurements, including instrumentation, modes of operation, strategies for data analysis, and strengths/limitations when characterizing polymer surfaces. The sections that follow describe applications in polymer science that benefit from characterization by ToF-SIMS, including thin films and coatings, polymer blends, composites, and electronic materials. The examples selected for discussion showcase the three standard modes of operation (spectral analysis, imaging, and depth profiling) and highlight practical considerations that relate to experimental design and data processing. We conclude with brief comments about broader opportunities for ToF-SIMS in polymer science.Item Coating and Doping of Ge QDs(2016-01-14) Oliva-Chatelain, Brittany Lynn; Barron, Andrew R; Billups, W. E.; Verduzco, RafaelThe ability to incorporate a dopant element into nanocrystals (NCs) and quantum dots (QDs) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications, particularly solar applications. Unlike doping of traditional bulk semiconductors materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping), or within the surrounding matrix (m-doping). A range of attempts to dope Ge QDs both during and post-synthesis are reported here. The QDs have been characterized by TEM, XPS, and I/V measurements of SiO2 coated QD thin films in test cells using doped Si substrates. The solution synthesis of Ge QDs by the reduction of GeCl4 with LiAlH4 results in Ge QDs with a low level of chlorine atoms on the surface; however, during the H2PtCl6 catalyzed alkylation of the surface with allylamine, chlorine functionalization of the surface occurs resulting in p-type doping of the QD. A similar location of the dopant is proposed for phosphorus when incorporated be the addition of PCl3 during QD synthesis; however, the electronic doping effect is greater. The detected dopants are all present on the surface of the QD (s-type), suggesting a self-purification process is operative. Attempts to incorporate boron or gallium during synthesis were unsuccessful. The silica coating of these particles was successful using a modified Stöber method. Monodispersed silica nanoparticles 20 nm in diameter were synthesized with Ge QDs as seeds. The resulting structures comprise of Ge QD core within a silica sphere. Films of these particles result in an average QD…QD distance of 9.6 nm, which is less than the maximum distance required for good electron transfer (10 nm). Film thickness and annealing tests were done to optimize the cells. These cells were tested for efficiency, and it was found that the phosphorus doped quantum dots and the undoped quantum dots both produced the highest photo induced current on n-type silicon wafers at ¼ of the maximum concentration of these particles with the phosphorus doped quantum dots producing a higher efficiency overall. Thermal annealing the films prior to deposition of the front and back contacts enabled a doubling in the cell efficiency, but did not show any marked increase in the density or crystallinity of the films.Item Compression induced stiffening and alignment of liquid crystal elastomers(2016-02-16) Verduzco, Rafael; Agrawal, Aditya; Chipara, Alin Cristian; Rice University; United States Patent and Trademark OfficeIn some embodiments, the present disclosure provides methods of strengthening liquid crystal elastomers. In some embodiments, such methods include a step of placing the liquid crystal elastomer in an environment that applies dynamic stress to the liquid crystal elastomer. In further embodiments, the methods of the present disclosure also include a step of providing liquid crystal elastomers for placement in an environment that applies dynamic stress. In some embodiments, the liquid crystal elastomer is in a nematic phase before or during the application of dynamic stress. In some embodiments, the application of dynamic stress enhances the stiffness of the liquid crystal elastomer by more than about 10%. Further embodiments of the present disclosure pertain to liquid crystal elastomers that are made by the methods of the present disclosure.Item Conductive Polymeric Interfaces for Cell-Material Communication and Signal Amplification in Microbial Bioelectronics(2022-04-21) Tseng, Chia-Ping; Verduzco, RafaelBioelectronics is the integration of biology with microelectronic devices. The combination of biology with microelectronics can potentially provide new systems for electricity generation, chemical production, environmental sensing, health diagnosis, disease treatment, a greater understanding of biology, and biomimetic materials and devices. Microelectronic devices are traditionally based on hard materials and rely on electronic signals while biology uses soft materials and a combination of ionic, molecular, and electron transfer for communication and signaling. Therefore, producing functional devices through the integration of these two fields requires addressing fundamental challenges in material properties, forms of signaling and communication, biocompatibility, and structures across various length scales. This thesis focuses on the development of functional electrode surface and polymeric networks and the fabrication of novel microbial bioelectronic devices to enhance bidirectional electrical and molecular communication. To bridge the gap between the biology and electronic worlds and improve the communication between them, this thesis pinpoints the solution for three key challenges including stable microbial adhesion, microbial patterning, and signal amplification. Prior research has developed and engineered two or three-dimensional biology-material interface layers to achieve dense microbial encapsulation, efficient electron transfer, and better nutrient and waste transport. However, we still lack electrode modification approaches that can be deposited easily and cheaply on an electrode surface, are amenable to patterning, and produce a significant enhancement to current densities. This thesis shows a solution-processable conductive polymer thin film that readily modifies the electrodes for diverse bioelectronics that take advantage of the high current density and microbial patterning on a surface. Furthermore, the integration of novel bioelectronic devices, specifically organic electrochemical transistor (OECT), with the microbes and enzymes demonstrates the power of amplifying minuscule electronic and ionic signals from biological entities compared to traditional three-electrode electrochemical systems. This research will lead to robust devices for monitoring enzymatic and microbial activities and benefit the material design and development of microbial bioelectronics for a broad class of sensitive and responsive biosensors.