Polycondensation reaction was carried out for synthesizing rigid-rod polymer hPBI. Various molar ratios (50:1, 25:1, and 15:1) of 2-hydroterephthalic acid and 5-hydroisophthalic acid were also introduced in the synthesis for articulated rigid-rod polymer a-hPBI. The polymers were further derivatized with 1,3-propanesulton for pendants of lithium ionomer to become water soluble polyelectrolytes hPBI-PS(Li+) and a-hPBI-PS(Li+), respectively. Lithium salt doped cast film of the rigid-rod polyelectrolyte hPBI-PS(Li+) showed a room-temperature DC conductivity parallel to film surface as high as 4.02¡Ñ10-3 S/cm. Molecular weight of the rigid-rod polyelectrolyte was low indicating a small molecular aspect ratio. In cast film, the molecules were randomly distributed and highly isotropic facilitated Li cations mobility for a high film conductivity. The conductivity was also insensitive to the anion of lithium salt. No apparent layered structure was revealed by scanning electron microscope suggesting that the cast films had near three-dimensionally isotropic structure and conductivity.

Polymer photovoltaic cell (PV cell) utilizes a polymer to absorb photons for generating excitons. When excitons are separated into electrons and holes, the device has the photovoltaic effect. Polymer light emitting diode (PLED) injects electrons and holes respectively from cathode and anode into a polymer emission layer. Some of the electrons and the holes would recombine to induce light emission. This research used a heterocyclic aromatic rigid-rod polymer poly-p-phenylene- benzobisoxazole (PBO) as the opto-electronic layer, and a conducting material of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) as the hole transport layer. PV cells were fabricated using indium-tin-oxide (ITO) as anode and aluminium as cathode. Same layer arrangement was applied for PLEDs. These two kinds of devices were measured for electrical and optical response. It was evidenced that the addition of PEDOT:PSS layer facilitated the separation of excitons into electrons and holes at the PBO/PEDOT:PSS interface. Insertion of a LiF layer between PBO layer and Al cathode reduced their energy band gap and facilitated charge transport leading to an enhanced efficiency for PV cells and PLEDs. Thickness variations were found on spun PBO layer. According to emission intensity, we knew that the PBO layer quality was significant for electroluminescence. Introduction of a PEDOT:PSS layer improved the interface between ITO and PBO. The thickness of PEDOT:PSS layer depended on the ITO surface roughness. With a PEDOT:PSS layer, the opto-electronic efficiency of PV cell and PLED was improved.

Poly-p-phenylenebenzobisoxazole (PBO) and carbon nanotube (CNT) contain fully conjugated rod like backbone entailing excellent mechanical properties, thermo -oxidative stability and solvent resistance. Rigid-rod PBO is commonly processed by dissolving in methanesulfonic acid or Lewis acid. A CNT of multi-wall carbon nanotube (MWNT) was dissolved in a Lewis acid solution of PBO for dispersion, and then spun for thin film. MWNT concentration in the films was from zero up to 5 wt. %. Compared to that of pure PBO film, all PBO/MWNT composite films retained same but enhanced UV-Vis absorption peaks, according to MWNT concentration, showing that PBO and MWNT did not have overlapping electron orbitals affecting their energy gaps. The composite films were excited at 325 nm using a He-Cd laser for photoluminescence (PL) emission. All PL spectra had maximum intensity at 540 nm indicative of yellow-green light emission. The composite films were fabricated as light emitting diodes using indium-tin-oxide/glass as substrate and anode, as well as vacuum evaporated Al as cathode for respectively hole and electron injectors. In these light emitting devices, MWNT doped PBO would decrease threshold voltage for about 2 V. Up to 0.1 wt. % of MWNT, the device emission current was increased two orders of magnitude than those of the devices without MWNT. Further increase of MWNT caused a successive decrease in electroluminescence emission intensity attributed to a quench effect from aggregations of MWNTs. UV epoxy resin was applied to package the mono-layer and bilayer PBO light emitting devices. The UV epoxy resin had some gas release during encapsulation. The devices were packaged with vacuum and without vacuum encapsulation. It was demonstrated that the device encapsulation reduced its demise from water and oxygen. The vacuum encapsulation could remove gaseous volatile of the device to inhibit oxygen and moisture to prolong device lifetime. The main degradation of light emitting device was the oxidization of cathode. The interactions between nitrogen of PBO and H2O caused the formation of hydrogen bonding at room temperature. Oxygen and moisture diffused into PBO polymer and were suspected to form mid-gap state for the polymer. The mid energy band disappeared upon heat treatment before encapsulation. A device under a higher bias voltage was found to have a shorter lifetime, but a larger EL emission intensity. The EL emission intensity was not a constant under a constant current bias. The vacuum encapsulated device had two or twenty times lifetime than, respectively, the device encapsulation without vacuum evacuation or in ambient conditions. The sandwich structure of ITO/PBO/Al had no observable photovoltaic effect due to insufficient exciton separation into electrons and holes. Poly(2,3-dihydro thieno-1,4-dioxin):polystyrenesulfonate (PEDOT:PSS), a hole transferring medium, was spun into a thin-film between PBO and indium-tin-oxide to facilitate photovoltaic (PV) effect by forming a donor-acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for the PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and the maximum short circuit current (Isc) were achieved with a LiF thickness of 1-2 nm due to possible electric dipole effect leading to an increase of Voc from 0.7 V to 0.92 V and of Isc from about 0.1

A heterocyclic aromatic rigid-rod polymer poly-p-phenylene-benzobisoxazole (PBO) was applied as the opto-electronic layer¡Fand a conducting material of poly(3,4-ethylenedioxythio-phene):poly(4-styrenesulfonic acid) (PEDOT: PSS) was used as the hole transport layer. Aluminum (Al) and indium tin oxide (ITO) were served as device cathode and anode¡Arespectively, fabricated into a bi-layer structure of ITO/PEDOT:PSS/PBO/Al for electrical and luminescence responses. This research demonstrated an increase of current density and a decrease of threshold voltage with a decrease of PBO layer thickness from 90 nm to 27 nm to facilitate electron tunneling and electron-hole recombination. With a lower spin coating speed, polymer chain would aggregate and inter-penetrate resulted in red-shift of electroluminescence (EL) emission spectrum. Furthermore, micro-cavity effect might influence EL spectrum by varying layer thickness. Modulation of PBO layer thickness led to tunable EL emission color. It was also demonstrated that an increase of current density and a slightly decrease of threshold voltage with a PEDOT:PSS film thickness changing from 96 nm to 17 nm at a constant PBO layer thickness of 90 nm. Micro-cavity effect thus influenced EL emission for a tunable emission color. Photolithography was applied to obtain ITO substrate of grating depth of periodic variation and then coated with a PEDOT:PSS leading to a grated PEDOT:PSS layer of periodic thickness. This led to ITO/PEDOT:PSS/PBO/Al device showing broadened EL emission spectra.

No description available.

In this research, we investigated a novel rigid-rod polymer sPBI for mono-layer polymer light emitting diode (PLED) fabrication and luminescence emission. sPBI could be a luminescent polymer with a low threshold voltage of 4.5 V and green light electroluminescence emission (530 nm). Its SO3H pendant attached to the p-phenyl ring improved electronic delocalization along the backbone resulted in a red shift of the absorption spectrum. By attaching propanesulfonated pendants to the heterocyclic moiety of intractable fully conjugated sPBI, water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) was synthesized to promote its processibility in water or common organic solvent. This water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) was fabricated for polymer light-emitting electrochemical cells (PLECs) with LiCF3SO3 (LiTf) or LiN(CF3SO2)2 (LiTfSI) dopants for investigating the influence of propanesulfonated pendants as well as dopants on the opto-electronic emission and the room-temperature DC conductivity. The effect of lithium salts (LiTf or LiTfSI) on photoluminescence color of doped sPBI-PS(Li+) films was negligible. sPBI-PS(Li+) PLECs doped with 0.41 and 1.01 wt. % of LiTfSI showed higher green light electroluminescence emission (514 nm) with a lower threshold voltage of 3.0 V and -4.6 V, respectively. Emission brightness of the sPBI-PS(Li+) PLEC did not raise upon increasing the ionic conductivity of the luminescent layer.

ABSTRACT Light emitting diodes of non-fully conjugated coil-like homopolymers and fully conjugated rigid-rod homopolymers with electron withdrawing or donating group were studied. A series of Poly[2,2-(m-2-X-phenylene)-4-4¡A-hexafluoroisopropane- bibenzoxazoles] (6F-PBO-X, with X = amine, hydrogen and nitro) and poly-p-(2-X- phenylene)-benzobisoxazole (PBO-X, with X = amine, hydrogen and nitro) were synthesized for light emitting diode applications to observe electroluminescence emission affected by electron withdrawing or donating group. All polymers were fabricated identically to form bi-layer light emitting diodes. In the devices, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonite)(PEDOT:PSS) was applied to be a hole transport layer; indium tin oxide (ITO) was the anode; and aluminum was the cathode. Devices of the non-fully conjugated coli-like polymers (6F-PBO-X) and the fully conjugated rigid-rod polymers (PBO-X) all showed threshold voltage about 4 V. In the electroluminescence (EL) spectrum, the maximum intensity of non-fully conjugated polymer (6F-PBO-X) with amine (-NH2), hydrogen (-H) or nitro (-NO2) functional group was at 499 nm, 505 nm and 515 nm, respectively, showing a 20 nm wavelength shift. From ¡VNH2, -H and ¡VNO2 groups, their Commission International de l`Eclairage (C. I. E.) coordinates were (0.30, 0.46), (0.34, 0.45) and (0.40, 0.46), respectively. The EL maximum intensity for fully conjugated rigid-rod polymer PBO-X was at 521 nm (-NH2) and 474 nm (-NO2) showing a 50 nm wavelength shift. Their C. I. E. coordinates were (0.42, 0.45) and (0.25, 0.38), respectively. This is attributed to the fully conjugated, collinear, coplanar, rigid-rod polymers (PBO-X) backbone readily affected by the push-pull functional groups showing a large red shift.

This dissertation aims to develop, characterize, and fundamentally understand a new class of materials termed "molecular ionic composites" (MICs). MICs show promise as next-generation solid electrolytes for batteries. MICs form when mixing a rigid polyanion with purely ionic fluids, and they behave mechanically as a solid but contain a high density of ions that move nearly as in a neat liquid. Specifically, prototypical MICs are based on solutions of the rigid-rod polyelectrolyte poly(2,2'-disulfonyl-4,4'-benzideneterephthalamide) (PBDT), which forms a double helix, combined with imidazolium-based ionic liquids (ILs). The IL comprises 75-97 wt% of the final solid, even though the Young's modulus can reach ~ 2 GPa at 80 wt% IL. We propose that these properties are driven by a biphasic internal structure in MICs corresponding to IL-rich "puddles" (an interconnected liquid phase) and PBDT-IL associated "bundles" where IL ions form the collective electrostatic associations that cause the MICs to be a solid. Through this dissertation I will discuss a wide variety of MICs that have been created through the use of two different formation processes, the "ingot" method and the "solvent casting" method, which allow for the use of many different ionic fluid sources to further tune MIC properties. The following chapters build to the fundamental knowledge and our current understanding of the wide variety of materials that can be created from PBDT and IL. / Doctor of Philosophy / Battery electrolytes, biosensors, and hydrogels all depend on new materials for next-generation applications. For these new materials to be used characterization on the interactions, morphological restrictions, and/or what unique internal structures used to generate their properties must be performed. Through This analysis using common polymeric characterization techniques these materials can be further optimized. This dissertation highlights a new class of materials termed "molecular ionic composites" (MICs) which are formed from a rigid double helical polymer, poly(2,2'-disulfonyl-4,4'-benzideneterephthalamide) (PBDT), and fluids composed entirely of ions, including ionic liquids (ILs). These composite systems feature a unique combination of properties including high thermal stability, mechanical stability, and excellent ionic conductivity, all of which are highly tunable through the amount of PBDT incorporated or the fluid ion types. Chapters 3, 4, 5, and 6 present fundamental investigations of MICs to determine how tunable they are, the processes by which they form, and the various ways we can fabricate them. Chapter 7 describes the creation of another impressive material formed from PBDT-low-polymer-content hydrogels. These studies are intended to provide deeper understanding of the behaviors of these unique materials and how they may be used in the future.

Among the myraid energy storage technologies, polymer electrolytes have been widely employed in diverse applications such as fuel cell membranes, battery separators, mechanical actuators, reverse-osmosis membranes and solar cells. The polymer electrolytes used for these applications usually require a combination of properties, including anisotropic orientation, tunable modulus, high ionic conductivity, light weight, high thermal stability and low cost. These critical properties have motivated researchers to find next-generation polymer electrolytes, for example ion gels. This dissertation aims to develop and characterize a new class of ion gel electrolytes based on ionic liquids and a rigid-rod polyelectrolyte. The rigid-rod polyelectrolyte poly (2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT) is a water-miscible system and forms a liquid crystal phase above a critical concentration. The diverse properties and broad applications of this rigid-rod polyelectrolyte may originate from the double helical conformation of PBDT molecular chains. We primarily develop an ionic liquid-based polymer gel electrolyte that possesses the following exceptional combination of properties: transport anisotropy up to 3.5×, high ionic conductivity (up to 8 mS cm⁻¹), widely tunable modulus (0.03 – 3 GPa) and high thermal stability (up to 300°C). This unique platform that combines ionic liquid and polyelectrolyte is essential to develop more advanced materials for broader applications. After we obtain the ion gels, we then mainly focus on modifying and then applying them in Li-metal batteries. As a next generation of Li batteries, the Li-metal battery offers higher energy capacity compared to the current Li-ion battery, thus satisfying our requirements in developing longer-lasting batteries for portable devices and even electric vehicles. However, Li dendrite growth on the Li metal anode has limited the pratical application of Li-metal batteries. This unexpected Li dendrite growth can be suppressed by developing polymer separators with high modulus (~ Gpa), while maintaining enough ionic conductivity (~ 1 mS/cm). Here, we describe an advanced solid-state electrolyte based on a sulfonated aramid rigid-rod polymer, an ionic liquid (IL), and a lithium salt, showing promise to make a breakthrough. This unique fabrication platform can be a milestone in discovering next-generation electrolyte materials. / Ph. D. / Among the myraid energy storage technologies, polymer-based electrolytes have been widely employed in diverse applications such as fuel cell membranes, battery electrolytes, “artificial muscle” mechanical actuators, reverse-osmosis membranes and solar cells. The materials used for each of these applications usually require a specific combination of properties, which include anisotropic orientation, tunable mechanical stiffness (modulus), high ionic conductivity, light weight, high thermal stability and low cost. These critical properties have motivated researchers to find next-generation polymer-based electrolytes, for example “ion gels” that consist of a polymer combined with ionic liquids or salts. This thesis describes development of an ion gel that possesses the following exceptional combination of properties: high ionic conductivity (up to 8 mS cm^-1), widely tunable modulus (0.03 ‒ 3 GPa), ion transport anisotropy up to 3.5×, and high thermal stability (up to 300°C). Thus, this unprecedented material shows liquid-like ion motions inside a matrix with solid-like stiffness, and in a material that can withstand extreme temperatures and will not burn. After obtaining these ion gels, we are then mainly focusing on modifying them for application in safe and high density Li-metal batteries. As a next generation of Li batteries, the Li-metal battery offers higher energy capacity compared to the current Liion battery, thus satisfying our requirements in developing longer-lasting batteries for portable devices and even electric vehicles. However, Li dendrite growth on the Li metal anode has limited the pratical application of Li-metal batteries. This unexpected Li dendrite growth can be supressed by developing polymer electrolytes with high modulus (~ GPa), while maintaining sufficient ionic conductivity (~ 1 mS/cm) for efficient battery operation. In short, this thesis describes an advanced solid-state electrolyte based on a kevlar-like (sulfonated aramid) rigid-rod polymer, an ionic liquid (IL), and a lithium salt, showing promise to make a breakthrough and enable practical Li-metal batteries. Furthermore, the unique fabrication platform for these ion gels represents a new paradigm for discovering next-generation electrolyte materials for a wide variety of applications.

Poly-p-phenylenebenzazoles (PBXs) are heterocyclic aromatic rigid-rod liquid-crystalline polymers with fully conjugated backbone having excellent thermo-oxidative, as well as dimensional stabilities. PBXs are considered to be multifunctional polymers of superior mechanical tenacity, non-linear optical response, and electrical properties. The fully conjugated PBX polymers are deemed to have excellent opto-electronic properties. In the last decade, molecular light emitting diodes (LEDs) have been investigated intensively for having distinct advantages as an advanced opto-electronic technology. This dissertation leads to rigid-rod polymer thin-films and mono-layer devices fabricated from acidic solutions. Photoluminescence (PL) spectra for poly-p-phenylenebenzobisthiazole (PBT) freestanding film were measured over a temperature range of 67 K to 300 K showing distinct electron-phonon interaction. Using an Mg cathode, the mono-layer PBT LEDs displayed a diodic electric response with a threshold voltage as low as 1 V. A blue shift in the maximum emission wavelength of the electroluminescence (EL) spectra was also observed with increasing electrical injection energy. For the multi-layer LEDs based on PBT using the same electrodes, the p-type/n-type bi-layer structure showing the most enhanced EL emission, and the tri-layer heterojunction had the least threshold voltage using the same electrodes. Our results indicated that the heterojunction architecture could be applied to balance charge carriers for increasing EL intensity. Meanwhile, the investigation also revealed the advantage in using the extra PBT layer for increasing both EL emission intensity and injection efficiency by lowering its threshold voltage. Two schemes for making uniaxial freestanding films and LED devices for polarized optical absorption and emission were processed from uniaxial poly-p-phenylenebenzobisoxazole (PBO) fiber. The PL of the uniaxial PBO films demonstrated an emission intensity ratio I¡ü/I¡æas high as 5. Anisotropically processed mono-layered PBO LED showed a markedly decreased threshold voltage from 7 V of the isotropic PBO device to 5 V. The polarization effects in optical absorption, PL and EL emissions were acquired and correlated with the uniaxial orientation of the rigid-rod PBO polymer. The molecular modification investigated the opto-electronic properties of poly-2,2'-m-phenylene-5,5'-bibenzimidazole (Pbi) with PBT physical blends, and monolithic 6F-PBO-OH-co-6F-PBO-di(OC10H21) copolymers. Partially conjugated polymer Pbi and fully conjugated polymer PBT were mixed for luminescence study. Their absorption spectra showed superposition of individual absorption response indicating no inter-molecular energy transfer. However, the PL and the EL emission demonstrated a blue shift with increasing Pbi content. This was attributed to the rigid-rod configuration or the aggregation of PBT perturbed by mixing with coil-like Pbi. It was recognized that the backbone of the fully conjugated rigid-rod PBT was collinear having more charge delocalization than that of not fully conjugated coil-like Pbi. The diode threshold voltage of the physical blends varied from 4 V to 14 V with decreasing PBT content. Another molecular modification was changing the composition of 6F-PBO copolymers. Their PL emission exhibited excellent chromatic tuning range from green to blue emission. The Commission Internationale de l¡¦Eclairage (C. I. E.) coordinates of the copolymer EL emission were from (0.25, 0.53) to (0.24, 0.31) covering a wide visible range and demonstrating a white light emission. Atomic substitution of the rigid-rod polymers was utilized to examine individual atomic contribution for luminescence emission. The hydrogen bond effect for PBO-OH and PBO was evidenced in a major Stoke¡¦s shift to a longer wavelength because of protonic transfer on the excited state. Elemental electronegativities affected the delocalization of the £k electron leading to a blue shift in absorption spectra as shown in case of PBO and PBT. The PBO molecule was more collinear and co-planar, providing more charge delocalization than PBT. However the absorption edge of the PBT was about 30 nm higher than that of PBO. This suggested that the electronegativities affected the molecular delocalization. Using the solid-state physics with pseudofunction (PSF) calculation, there was good match between absorption spectra and calculated excitation energies for the rigid-rod polymer systems.