Browsing by Subject "Conducting polymers"
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Item Biodegradable electroactive materials for tissue engineering applications(2008-12) Guimard, Nathalie Kathryn, 1979-; Schmidt, Christine E.; Sessler, Jonathan L.This dissertation focuses on the development of biomaterials that could be used to enhance the regeneration of severed peripheral nerves. These materials were designed to be electroactive, biodegradable, and biocompatible. To render the materials electroactive the author chose to incorporate conducting polymer (CP) units into the materials. Because CPs are inherently non-degradable, the key challenge was to create a CP-based material that was also biodegradable. Two strategies were explored to generate a biodegradable CP-based material. The first strategy centered around the incorporation of both electroactive and biodegradable subunits into a copolymer system. In the context of this approach, two bis(methoxyquaterthiophene)-co-adipic acid polyester (QAPE) analogues were successfully synthesized, one through polycondensation (giving undoped QAPE) and the second through oxidative polymerization (giving doped QAPE-2). QAPE was found to be electroactive by cyclic voltammetry, bioerodible, and cytocompatible with Schwann cells. QAPE was doped with ferric perchlorate, although only a low doping percentage was realized (~8%). Oxidative polymerization of a bis(bithiophene) adipate permitted the direct synthesis of doped QAPE-2, which was found to have a higher doping level (~24%). The second strategy pursued with the goal of generating an electroactive biodegradable material involved covalently immobilizing low molecular weight polythiophene chains onto the surface of crosslinked hyaluronic acid (HA) films. HA films are not only biodegradable and biocompatible, but they also provide mechanical integrity to bilayer systems. Dicyclocarbodiimide coupling of carboxylic acids to HA alcohol groups was used to functionalize HA films. The HA-polythiophene composite is still in the early stages of development. However, to date, thiophene has been successfully immobilized at the surface of HA films with a high degree of substitution. The author has also shown that thiophene polymerization can be achieved at the surface of these functionalized films and that the extent of polymer immobilization appears to be affected by the presence of immobilized thiophene. The results reported in this dissertation lead the author to suggest that it is possible to generate biodegradable electroactive materials. Further, she believes that with additional optimization these materials may prove beneficial for the regeneration of peripheral nerves and possibly other tissues that respond favorably to electrical stimulation.Item Conducting polymers for n-type semiconductors, molecular actuators, and organic photovoltaics(2013-08) Dinser, Jordan Alyssa; Holliday, Bradley J.The majority of conjugated polymers are more stable as p-doped materials than n-doped materials. Stable n-doped polymers are still desirable and for all polymer OPVs, pLEDS, n-channel FETs, and other polymeric electronic devices. The use of donor-acceptor architectures has led to improvements in n-type polymer performance. The approach taken here has been to include a metal-coordination site within a donor-acceptor polymer backbone in order to explore the effect of redox matching between the conjugated polymer backbone and the transition metal center. Conducting polymers have shown promise as polymeric actuators for prosthetics, robotics, and dynamic braille displays. For the majority of conducting polymers, the actuation mechanism is a bulk phenomenon related to the uptake and expulsion of counterions. This performance may be improved by incorporating monomers which display geometry changes as a function of oxidation state into the polymer backbone. The molecular-level actuation should additively yield a macroscopic actuation that would surpass as well as compliment the bulk mechanism discussed above. We have synthesized a conjugated polymer which incorporates the sym-dibenzocyclooctatetraene moiety, which is known to undergo a change in geometry from a tub-shaped neutral structure to a planar radical anion, into the polymer backbone. The solution processability of conjugated polymers promises large-scale roll-to-roll processing for organic photovoltaics. However, the use of thin active layers in the majority of high efficiency devices reported to date prohibits this. The recently reported donor-acceptor copolymer KP115 shows high efficiencies in polymer-fullerene blend bulk heterojunction devices even with very thick active layers. This has been reported to be unrelated to the morphology of the blends. By further characterizing this material and preparing derivatives of this polymer, we aim to relate the unique performance of these devices to a structural feature of the polymer. It is proposed that the low recombination rates observed for these blends may be due to the presence of discrete donor and acceptor units in the polymer backbone. In order to further explore this idea, we have a prepared a derivative of KP115 in which a conjugation-breaking meta-phenyl linkage has been introduced between the silolodithiophene unit and the dithienylthiazolo[5,4-d]thiazole unit.Item Creating more effective functional materials: altering the electronics of conducting metallopolymers for different applications.(2014-05) Raiford, Matthew Thomas; Holliday, Bradley J.; Humphrey, Simon M; Anslyn, Eric V; Jones, Richard A; Freeman, Benny DConducting metallopolymers possess attractive electronic properties for use in sensors, photoelectronic devices, catalysts, and other applications. Modification of the conducting polymer backbone, through chemical or electrochemical methods, enables control of catalytic, electronic, and optical properties of the metal via inductive modulation of the electron density. Understanding in detail the relationship between the metal and polymer backbone could lead to more effective metallopolymer materials. We hope to study this relationship by probing the band gaps, excited state energy levels, catalytic activity, and sensor function in four metallopolymer systems. Devices with sub-stochiometric ratios of Cu2ZnSnS4 NPs (CZTS: (Cu2Sn)1-xZn1/xS)(0≥x≥0.75)) grown in Cu(II) conducting metallopolymers were produced to study band gap tuning in hybrid materials. The valence and conductance bands of CZTS (x = 0.60) aligned with the HOMO/LUMO of the Cu(II) metallopolymer. Changing the alignment facilitated charge transfer in the hybrid material, leading to photovoltaic materials with efficiencies of ~0.1%. Chemoresistive ionophore sensors were developed by incorporating selective binding groups, such as thiourea, into conducting polymer backbones. Thiourea monomers and polymers showed high selectivity for Pb(II) ions over many competitive ions. XPS experiments demonstrated that reversible chelation of Pb(II) ions could be achieved through a simple uptake/rinse process. The conductivity of the thiourea polymer increased fifty-fold, from 7.75×10−2 S/cm2 to 3.5 S/cm2, after Pb(II) exposure. Sensitivity measurements indicated the sensors have limits of detection near 10−10 M. Highly conjugated ligands were synthesized to explore effective sensitization of visible and near-IR emitting lanthanides. (3,4-ethylenedioxy)thiophene was appended to dipyridophenazine and dipyridoquinoxaline to introduce a group that could be easily electropolymerized. These bi-functional ligands emitted from π-π* and an inter-ligand charge transfer excited states, and therefore, two distinct triplet states were observed. These separate energy pathways allowed for efficient sensitization of both visible (Tb(III), Eu(III), Dy(III)) and near-IR emitting (Nd(III), Yb(III), Er(III)) ions. Finally, we explored the oxidation of a rhodium-containing conducting metallopolymer and the subsequent effect on the activity of the metal center. Oxidation of the backbone led to ancillary ligand attenuation, allowing for control of the catalytically active species in the conducting metallopolymer. Rh(I,III) monomer and metallopolymer catalytic studies showed potential for new heterogenous/homogeneous hybrid catalysts.Item Design, synthesis, and characterization of a novel biodegradable, electrically conducting biomaterial(2001-08) Rivers, Tyrell Jermaine; Schmidt, Christine E.This text describes the rational design, synthesis, and characterization of a new biomaterial with a unique set of properties. The polymer is biodegradable and biocompatible and can be rendered conductive by treatment with iodine vapor. The synthesis of this biomaterial was achieved using conducting oligomers of pyrrole and thiophene that are connected via flexible aliphatic regions and degradable ester linkages. This material has promise for biomedical applications, particularly tissue engineering, in which a degradable polymer scaffold is desired to serve as an initial template for tissue growth. Furthermore, the electrically conducting property of the polymer is attractive since electrical fields and charges are known to stimulate healing of several tissue types including bone, skin, and nerve. Thus, the use of an electrically conducting polymer has the potential to allow one to locally deliver electrical stimulation directly to the site of damage, while also providing a physical template for cell growth and tissue repair.Item Improving capacitance and cyclability in microbial cellulose based ultracapacitors(2011-12) Young, Nathaniel James; Brown, R. Malcolm (Richard Malcolm), 1939-; Meyers, Jeremy P.Microbial Cellulose (MC) is a highly porous macromolecule with intrinsic properties that make it a useful substrate for conductive materials within ultracapacitors. MC has the potential to increase capacitance by serving as a high surface area substrate for conductive polymers and carbonaceous materials. Electrode surface area is a critical parameter in ultracapacitors because capacitance depends on the available active sites that are accessible to counter ions. Commercial ultracapacitors increase electrode surface area by adding microsize carbonaceous materials. Most commercial devices also require adhesive compounds to bind the conductive material to the substrate. Adhesive compounds increase sheet resistance and hinder overall capacitance. MC membranes possess highlyordered surface hydroxyl groups that readily bind to different types conductive materials and reduce the need for additive adhesive compounds. This thesis investigates three unique methods for converting a MC membrane into a working ultracapacitor electrode. In the first method, polypyrrole and carbon nanotubes (CNTs) are added to a medium of Acetobacter that incorporates the material into a homogeneous crystalline matrix of beta1,4 glucan chains. The resulting MC is a fully integrated membrane with a homogeneous embedded layer of conductive material. SEM imaging shows the conductive material is incorporated primarily at the core of the membrane. As a result, this electrode suffered from high sheet resistance and did not generate any significant capacitance. In the second method, a conductive ink consisting of CNTs, carboxymethyl cellulose (CMC), polypyrrole, and DI water was used to coat the surface of a dried cellulose membrane. After 12 hours, the ink dries and leaves a shiny black conductive layer on the membrane’s surface. CMC’s role in the ink is to increase viscosity and help bind the conductive material to the membrane surface. CMC is also a dielectric material that acts as an insulator to the polypyrrole and CNTs, and ultimately impedes electrical energy storage. In the final method, a MC membrane was soaked in aqueous and non aqueous pyrrole solutions, and polymerized with FeCl3 and Fe2(SO4)3. Single and double membrane device configurations were also investigated. Surface polymerization of pyrrole monomers proved to be the best method for converting microbial cellulose into a working electrode with good capacitance and cyclability.Item Molecular investigation of polypyrrole and surface recognition by affinity peptides(2011-12) Fonner, John Michael; Ren, Pengyu; Schmidt, Christine E.; Elber, Ron; Roy, Krishnendu; Georgiou, GeorgeSuccessful tissue engineering strategies in the nervous system must be carefully crafted to interact favorably with the complex biochemical signals of the native environment. To date, all chronic implants incorporating electrical conductivity degrade in performance over time as the foreign body reaction and subsequent fibrous encapsulation isolate them from the host tissue. Our goal is to develop a peptide-based interfacial biomaterial that will non-covalently coat the surface of the conducting polymer polypyrrole, allowing the implant to interact with the nervous system through both electrical and chemical cues. Starting with a candidate peptide sequence discovered through phage display, we used computational simulations of the peptide on polypyrrole to describe the bound peptide structure, explore the mechanism of binding, and suggest new, better binding peptide sequences. After experimentally characterizing the polymer, we created a molecular mechanics model of polypyrrole using quantum mechanics calculations and compared its in silico properties to experimental observables such as density and chain packing. Using replica exchange molecular dynamics, we then modeled the behavior of affinity binding peptides on the surface of polypyrrole in explicit water and saline environments. Relative measurements of the contributions of each amino acid were made using distance measurements and computational alanine scanning.Item Studies of conjugated polymer thin film morphology : effect on emission and charge transport(2007-05) Rozanski, Lynn June, 1980-; Vanden Bout, David A.Item Studies of conjugated polymer thin film morphology: effect on emission and charge transport(2007) Rozanski, Lynn June; Vanden Bout, David A.Since their discovery, semiconducting conjugated polymers have shown great promise as active materials for a range of electronic devices. Initially desired for their high quantum yield, conjugated polymers have become popular due to their low cost and potential to be transferred to existing technology. Conjugated polymers are liquid crystalline, packing into well ordered domains upon thermal annealing of the films, which often leads to complex polymer interactions that can affect their semiconducting properties such as charge transport, emission color and ultimately device efficiency. Film morphology is difficult to characterize, with the order often varying on the nanoscale within a film. Near field scanning optical microscopy (NSOM) combined with Atomic Force Microscopy (AFM) can probe the degree of order of a film on the nanoscale and correlate it to topography; this can then be related to changes in luminescence emission and device characteristics to infer how charges are moving within a film. The effect of morphology on device function can vary between polymer systems; for example, di-alkyl polyfluorenes (PFs), a popular blue emitter for LEDs, undergo fluorescence degradation from ketone-based defects. Ordering of PF films containing some chemical defects increased the energy transfer from pristine chains to defects, increasing the defects’ degrading effect on the film emission. In comparison, the air-stable di-alkyl polyphenylene ethynylenes (PPEs) have numerous chain interactions in the amorphous pristine film, but show evidence of fewer interactions between these chains after ordering the film rather than more interactions. PPE polymers with varied lengths of sidechains produce dissimilar electroluminescence intensities, due to differences in their morphologies that affected how charges moved and recombined within the films. Understanding the effect of changes in polymer film morphology on luminescence and charge movement will help future efforts in understanding more complex polymer interactions, such as seen in blended polymer films.Item Synthesis and characterization of electronic materials for photovoltaic applications(2010-05) Mejia, Michelle Leann; Holliday, Bradley J.; Cowley, Alan H.; Crooks, Richard M.; Dodabalapur, Ananth; Jones, Richard A.Electronic materials are of great interest for use in photovoltaics, sensors, light-emitting diodes, and molecular electronics. Hybrid Inorganic/Organic materials have been studied for device application due to their unique electronic properties. These properties result from the formation of bulk heterojunctions between inorganic (n-type) and organic (p-type) materials. However, due to incomplete pathways for charge transport and poor interfaces between materials, charge trapping and exciton recombination is often high. In an effort to alleviate these problems, we have developed an approach to fabricate bulk heterojunction materials via a seeded growth process. Electropolymerizable Schiff base complexes have been designed, synthesized, and utilized as precursors for conducting metallopolymers. The embedded metal centers are used as seed points for direct growth of size-controllable semiconductor nanoparticles within the polymer film leading to direct electronic communication between the two materials. The synthesis of CdS, CdSe, Ga₂S₃, CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, CuGa[subscript x]In[subscript x]-₁S₂, and CuGa[subscript x]In[subscript x]-₁Se₂ has been seen through TEM and EDX. Devices have been fabricated and current studies have focused on the photovoltaic characterization of these materials which have a PCE of 0.11%. As a second but closely related area, polymers have also been studied as organic semiconductors for device applications. However they are hard to process from solution and their polymeric structure can vary. Both of these problems can be solved by using well-defined solution processable oligomers. Thiophene oligomers have been synthesized and characterized through Single Crystal X-Ray Crystallography, Four Point Probe Conductivity, and Powder Diffraction. These oligomers have a well-defined structure and are solution processable from a variety of solvents which can then be used as models to predict and study the properties of polythiophene.Item The synthesis of novel conducting polymers and oligomers for use in electrical devices, drug delivery systems, and energy dynamics studies(2010-05) Villa, Monica Irais, 1982-; Holliday, Bradley J.; Jones, Richard A., 1954-Described herein are three projects centered on the synthesis of conducting polymer derivatives for various applications. The first is the novel synthesis of 9,9-dioctylfluorene-co-benzothiadiazole [F8BT] oligomers through solid phase synthesis for the study of the thermodynamics and kinetics of electron transfer in the polymer. The second endeavor involves the synthesis of a series of 4”,3’’’-dialkyl-2,2’:5’,2”:5”,2’’’:5’’’,2’’’’:5’’’’,2’’’’’-sexithiophenes for the studies on crystal packing and surface deposition of organic p-type semiconducting materials. Lastly is described the development of a conducting metallopolymer based on the ligand 2,6-Bis(4-(2,2’-bithiophen-5-yl)-1H-pyrazol-1-yl)pyridine for use in a drug delivery system.Item Understanding the processing-structure-property relationships of water-dispersible, conductive polyaniline(2009-05) Yoo, Joung Eun; Sanchez, Isaac C., 1941-Polyaniline (PANI), when doped with small-molecule acids, is an attractive candidate for organic and polymer electronics because of its high electrical conductivity. Its utility as functional components in electrical devices, however, has been severely restricted because such PANI has limited processibility stemming from its limited solubility in common solvents. To overcome this barrier, we have developed water dispersible PANI that is template polymerized in the presence of a polymer acid, poly(2-acrylamido-2-methyl-1-propanesulfonic acid), or PAAMPSA. The polymer acid serves two roles: it acts as a dopant to render PANI conductive and excess water soluble pendant groups provide dispersibility of PANI in aqueous media. While the introduction of polymer acids renders the conducting polymer processible, such gain in processibility is often accompanied by a significant reduction in conductivity. As such, PANI that is doped with polymer acids has only seen limited utility in organic electronics. Given the promise of conducting polymers in organic electronics in general, this thesis focuses on the elucidation of processing-structure-property relationships of PANI-PAAMPSA with the aim of ultimately improving the electrical conductivity of polymer acid-doped PANI. By controlling the molecular weight and molecular weight distribution of the polymer acid template, we have improved the conductivity of PANI-PAAMPSA from 0.4 to 2.5 S/cm. The conductivity increases with decreasing molecular weight of PAAMPSA, and it further increases with narrowing the molecular weight distribution of PAAMPSA. Strong correlations between the structure and the conductivity of PANI-PAAMPSA are observed. In particular, the crystallinity of PANI increases with increasing the conductivity of PANI-PAAMPSA. Given that the crystallinity qualifies the molecular order in PANI-PAAMPSA, we observe a linear correlation between molecular order and macroscopic charge transport in PANI-PAAMPSA. PANI-PAAMPSA forms electrostatically stabilized sub-micron particles during polymerization due to strong ionic interactions between the sulfonic acid groups of PAAMPSA and aniline. When cast as films, the connectivity of these particles must play an important role in macroscopic conduction. The size and size distribution of PANI-PAAMPSA particles is strongly influenced by the molecular characteristics of polymer acid template. Templating the synthesis of PANI-PAAMPSA with a higher molecular weight PAAMPSA results in larger particles, and templating with a PAAMPSA having a larger molecular weight distribution results in a large size distribution in the particles. Because conduction in PANI-PAAMPSA films is governed by how these particles pack, the macroscopic conductivity of PANI-PAAMPSA films increases with increasing particle density, that is reducible from the molecular characteristics of PAAMPSA. Moreover, PANI-PAAMPSA particles are structurally and chemically inhomogeneous. The conductive portions of the polymer preferentially segregate to the particle surface. Conduction in these materials is therefore mediated by the particle surface and conductivity thus scales superlinearly with particle surface area per unit film volume. We further have improved the electrical conductivity of PANI-PAAMPSA by more than two orders of magnitude via post-processing solvent annealing with dichloroacetic acid (DCA). Since DCA is a good plasticizer for PAAMPSA and its pKa is lower than that of PAAMPSA (pKas of DCA and PAAMPSA are 1.21 and 2.41, respectively, at room temperature), DCA can effectively moderate the ionic interactions between PANI and PAAMPSA, thereby relaxing the sub-micron particulate structure arrested during polymerization. PANI-PAAMPSA can thus rearrange from a “compact coil” to an “extended chain” conformation upon exposure to DCA. Efficient charge transport is thus enabled through such “extended chain” PANI-PAAMPSA structure. DCA-treated PANI-PAAMPSA exhibits an average conductivity of 48 S/cm. The DCA treatment is not only specific to PANI-PAAMPSA. This treatment can also enhance the conductivity of commercially-available poly(ethylene dioxythiophene) that is doped with poly(styrene sulfonic acid), or PEDOT-PSS. Specifically, DCA-treated PEDOT-PSS exhibits a conductivity of 600 S/cm; this conductivity is the highest among polymer acid-doped conducting polymers reported so far. PANI-PAAMPSA can effectively function as anodes in organic solar cells (OSCs) whose active layer is a blend of poly(3-hexylthiophene), P3HT, and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Specifically, the OSCs with PANI-PAAMPSA anodes exhibit an average short circuit current density of 1.95 mA/cm², open circuit voltage of 0.52 V, fill factor of 0.38, and efficiency of 0.39 %. The use of DCA-treated PANI-PAAMPSA as anodes increases device performance (i.e., short circuit current density and thereby efficiency) of OSCs by approximately two and a half fold. The OSCs with DCA-treated PANI-PAAMPSA anodes exhibit short circuit current density and efficiency as high as 4.95 mA/cm² and 0.97 %, respectively. We demonstrated several factors that govern the electrical conductivity of polymer acid-doped conducting polymers. Design rules, such as those illustrated in this study, can enable the development of conducting polymers that is not only easily processible from aqueous dispersions, but also sufficiently conductive for electronic applications, and should bring us closer to the realization of low-cost organic and polymeric electronics.