OPTIMIZATION OF THE OPTICAL AND ELECTROCHEMICAL PROPERTIES OF DONOR-ACCEPTOR COPOLYMERS THROUGH FUNCTIONAL GROUP AND SIDE CHAIN MODIFICATION

Donor-acceptor copolymers have received a great deal of attention for application as organic semiconductors, in particular as the active layers in low-cost consumer electronics. The functional groups grafted to the polymer backbones generally dictate the molecular orbital energies of the final materials as well as aid in self-assembly. Additionally, the side chains attached to these functional groups not only dictate the solubility of the final materials, but also their morphological characteristics. The bulk of the research presented in this dissertation focuses on the synthesis and structure-property relationships of polymers containing novel acceptor motifs. Chapter 2 focuses on the synthesis of 1,2-disubstituted cyanoarene monomers as the acceptor motif for copolymerization with known donors. It was found that cyanation of both benzene and thiophene aromatic cores resulted in a decrease of the molecular orbital energy levels. Additionally, the small size of this functional group allowed favorable self-assembly and close π-stacking to occur relative to related acceptor cores carrying alkyl side chains as evidenced by UV-Vis and WAXD data. Chapter 3 describes the systematic variation of side chain branching length and position within a series of phthalimide-based polymers. Branching of the side chains on bithiophene donor units resulted in the expected increase in solubility for these materials. Furthermore, a correlation was found between the branching position, size, and the HOMO energy levels for the polymers. Additionally, it was demonstrated that branching the alkyl side chains in close proximity to polymer backbones does not disrupt conjugation in these systems. A novel acceptor motif based on the 1,3-indanedione unit is presented in Chapter 4. Despite the stronger electron withdrawing capability of this functional group relativeto phthalimide, it was found that polymers based on this unit have the same HOMO molecular orbital energy levels as those presented in Chapter 3. It was found, however, the presence of orthogonal side chains greatly enhanced the solubility of the final polymers. Additionally, UV-Vis and WAXD measurements revealed that thermal annealing had a profound effect on the ordering of these polymers. Despite the presence of orthogonal side chains, long range order and close π-stacking distances were still achieved with these materials. Finally, alkynyl “spacers” were used in Chapter 5 to separate the solubilizing alkyl side chains from the polymer backbones on bithiophene donor monomers. The alkynyl groups allowed for conjugated polymer backbones to be achieved as well as low HOMO energy levels. A correlation between the side chain size, π-stacking distances and HOMO-LUMO energy levels was measured in this polymer series

Development of a new chemical sensor based on plasma polymerized polypyrrole films

La present tesis contribueix a donar una nova visió dins de l'àrea de modificació de superfícies, la qual implica la nanoestructuració de substrats fent servir la tècnica d'auto-assemblatge per a dipositar sobre aquests un polímer conductor mitjançant deposició química en fase vapor per plasma. L'ús de polímers conductors ha despertat un creixent interès en el desenvolupament de sensors químics per a l'anàlisi de gasos en aplicacions d'enginyeria electrònica. La contínua reducció de mida en aquests dispositius ha encoratjat la proposta d'un mètode alternatiu per aconseguir estructures de rang nanomètric, així com per solucionar problemes com la falta d'adherència entre substrat i polímer, disminuir els límits de detecció o escurçar els temps de resposta.En aquesta investigació s'ha treballat amb monocapes amb un grup pirrol terminal per tal de potenciar la nucleació i creixement de pel·lícules de polipirrol polimeritzades mitjançant plasma. A més, les monocapes han aportat millores en l'adhesió interfacial de l'estructura polímer/metall. Així mateix, s'han dopat les pel·lícules primes de polipirrol per tal d'obtenir la seva forma conductora, les propietats elèctriques de les quals permeten utilitzar-ho com a sensor químic. La seva exposició a un vapor comporta canvis en la conductivitat del polímer, a través dels quals es pot identificar i quantificar l'esmentat analit.L'auto-assemblatge i la deposició del polímer són els factors claus en aquesta investigació. Per tant, s'han utilitzat diverses tècniques de caracterització de superfícies com XPS, TOF-SIMS, FT-IR o SEM, per estudiar les seves propietats físiques i químiques. Igualment, l'ús de l'AFM ha estat de gran ajut per investigar el procés de nucleació i la topografia de les pel·lícules. A més, la tècnica de les quatre puntes ha proporcionat una excel·lent eina per realitzar mesures de conductivitat a les pel·lícules primes. Finalment, les pel·lícules polimeritzades per plasma han mostrat una gran sensibilitat al diòxid de carboni, demostrant la seva capacitat per ser utilitzades com a sensors químics.La presente tesis contribuye a dar una nueva visión dentro del área de modificación de superficies, la cual implica la nanoestructuración de sustratos utilizando la técnica de auto-ensamblado para depositar sobre éstos un polímero conductor mediante deposición química en fase vapor por plasma. El uso de polímeros conductores ha despertado un creciente interés en el desarrollo de sensores químicos para el análisis de gases en aplicaciones de ingeniería electrónica. La continua reducción de tamaño en estos dispositivos ha alentado la propuesta de un método alternativo para conseguir estructuras de rango nanométrico, así como para solucionar problemas tales como la falta de adherencia entre sustrato y polímero, disminuir los límites de detección o acortar los tiempos de respuesta.En esta investigación se ha trabajado con monocapas con un grupo pirrol terminal para potenciar la nucleación y crecimiento de películas de polipirrol polimerizadas mediante plasma. Además, las monocapas han aportado mejoras en la adhesión interfacial de la estructura polímero/metal. Asimismo, se han dopado las películas delgadas de polipirrol para obtener su forma conductora, cuyas propiedades eléctricas permiten utilizarlo como sensor químico. Su exposición a un vapor conlleva cambios en la conductividad del polímero, a través de los cuales se puede identificar y cuantificar dicho analito.El auto-ensamblaje y la deposición del polímero son los factores claves en esta investigación. Por lo tanto, se han utilizado diversas técnicas de caracterización de superficies, como XPS, TOF-SIMS, FT-IR o SEM, para estudiar sus propiedades físicas y químicas. Igualmente, el uso del AFM ha sido de gran valor para investigar el proceso de nucleación y la topografía de las películas. Además, la técnica de las cuatro puntas ha proporcionado una excelente herramienta para realizar medidas de conductividad en películas delgadas. Finalmente, las películas polimerizadas por plasma han mostrado una gran sensibilidad al dióxido de carbono, con lo cual han demostrado su capacidad para ser utilizados como sensores químicos.This thesis contributes a new insight into surface modification involving substrates nanostructuration by self-assembly to deposit on them a conducting polymer through plasma enhanced chemical vapor deposition. The use of conducting polymers has gained growing interest in the development of chemical sensor arrays for gas analysis in electronic engineering applications. The size reduction in these devices has encouraged the proposal of an alternative method to achieve structures at nanometer range, as well as overcoming problems like lack of adhesion between substrate and polymer, lower limits of detection or shorten response times.The investigation has dealt with the use of pyrrole terminated monolayers to enhance the nucleation and growth of polypyrrole plasma polymerized films. In addition, monolayers provide an improvement in the interfacial adhesion of the polymer/metal structure. Furthermore, polymeric thin films have been doped to obtain the conducting form of polypyrrole, of which electric properties enable to use it as a chemical sensor. Exposure to vapors leads to changes in polymer conductivity, by which analytes can be identified and quantified.Self-assembly and polymer deposition are key factors in this research, as a consequence surface characterization techniques, such as XPS, TOF-SIMS, FT-IR or SEM, have been employed to study their physical and chemical characteristics. Especially interesting have been the use of AFM to investigate the nucleation process and the film topography. Moreover, the four-point probe technique has provided an excellent tool to perform conductivity measurements on thin films. Besides, plasma polymerized films have shown a high sensitivity to carbon dioxide in order to demonstrate their aptitudes to be utilized as a chemical sensor

EXPLORING THE STRUCTURE AND PROPERTIES OF NANOMATERIALS USING ADVANCED ELECTRON MICROSCOPY TECHNIQUES

Nowadays people are relying on all kinds of electronic devices in their daily life. All these devices are getting smaller and lighter with longer battery life due to the improvement of nanotechnology and materials sciences. Electron microscopy (EM) plays a vital role in the evolution of materials characterization which shapes the technology in today’s life. In electron microscopy, electron beam is used as the illumination source instead of visible light used in traditional optical microscopy, the wavelength of an electron is about 105 times shorter than visible light. By taking this advantage, the resolving power and magnification are greatly improved which gives us the ability to understand the morphology and the structure of smaller materials. Besides high resolution and high magnifications, the electron-matter interactions in electron microscopy are also very interesting and provide useful information. Typically, there are three types of post electron-matter interaction electrons, and they are: secondary electrons, backscattered electrons and transmitted electrons. Different signals are carried out with these electron-matter interactions, the most common techniques including electron dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED). In this dissertation, I will discuss how electron microscopy techniques approach complicated nanostructures, such as MnSb2Se4 nanorods to reveal the composition, structure, surfactant controlled size, and relative magnetic properties. Other important features such as mapping localized surface plasmon resonance (LSPR) using EELS and newly developed liquid cell scanning mode transmission electron microscopy (STEM) in situ observation are also presented

Optimizing Energy Conversion in Organic Materials via Processing and Morphological Design.

The performance and reliability of bulk heterojunction thin film polymer solar cells are inextricably linked to the three-dimensional nanoscale morphological structure of the photoactive materials, driven by the extent of phase separation between the polymer and fullerene components. To this end, well-established processing protocols to induce phase separation comprising high temperature and solvent vapor annealing have been employed to create optimal nanoscale morphologies. This thesis examines two fundamental approaches regarding the control of nanoscale morphology: (1) a novel environmentally benign processing method, and (2) the use of an all-conjugated gradient copolymer.PhDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120723/1/jamonoo_1.pd

A Survey on Compiler Autotuning using Machine Learning

Since the mid-1990s, researchers have been trying to use machine-learning based approaches to solve a number of different compiler optimization problems. These techniques primarily enhance the quality of the obtained results and, more importantly, make it feasible to tackle two main compiler optimization problems: optimization selection (choosing which optimizations to apply) and phase-ordering (choosing the order of applying optimizations). The compiler optimization space continues to grow due to the advancement of applications, increasing number of compiler optimizations, and new target architectures. Generic optimization passes in compilers cannot fully leverage newly introduced optimizations and, therefore, cannot keep up with the pace of increasing options. This survey summarizes and classifies the recent advances in using machine learning for the compiler optimization field, particularly on the two major problems of (1) selecting the best optimizations and (2) the phase-ordering of optimizations. The survey highlights the approaches taken so far, the obtained results, the fine-grain classification among different approaches and finally, the influential papers of the field.Comment: version 5.0 (updated on September 2018)- Preprint Version For our Accepted Journal @ ACM CSUR 2018 (42 pages) - This survey will be updated quarterly here (Send me your new published papers to be added in the subsequent version) History: Received November 2016; Revised August 2017; Revised February 2018; Accepted March 2018

Synthesis and characterization of functional polymeric materials for use in organic photovoltaics

Norbornene-type monomers with pendant oligothiophene donor and perylene diimide acceptor groups were synthesized and polymerized using ring-opening metathesis polymerization (ROMP) to yield donor and acceptor homopolymers. These semiconducting homopolymers were characterized by UV-Vis and fluorescence spectroscopy to determine absorbance maxima, emission and excitation profiles, optical bandgaps, molar absorbtivities, and quantum yields. The electrochemical behavior of the donor and acceptor materials was characterized by cyclic voltammetry to determine the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the organic semiconductors. Donor-acceptor diblock copolymers were synthesized using ROMP. Fluorescence spectroscopy demonstrated increased donor emission quenching with decreasing block length. Random donor-acceptor copolymers demonstrated almost complete quenching of the donor emission, likely due to increased donor-acceptor interfaces for charge transfer. Electron paramagnetic resonance spectroscopy (EPR) confirmed the formation of persistent donor radical cations and acceptor radical anions in the block copolymers. Small-angle X-ray scattering (SAXS) demonstrated bulk microphase separation with domain sizes between 24-28 nm. Furthermore, the formation of crystalline structure within the ordered microdomains was also observed. All of these studies indicate that the designed materials may be useful as the active layer in organic photovoltaic applications. As a route to functional hybrid materials, block copolymers containing a donor-segment and a Lewis-basic oligoethylene glycol segment, for preferential ZnO nanoparticle growth, were synthesized by ROMP. Photophysical and electrochemical characterization demonstrated that the donor electronic properties were maintained upon incorporation into the copolymer. SAXS was used to demonstrate lamellar morphology in bulk films of the symmetric block copolymers. ZnO nanoparticles were synthesized and incorporated into composite thin films with the block copolymers. These composite films demonstrated high photoluminescence quenching, which increased upon thermal annealing, as a result of favorable charge transfer from the photo-excited donor to the ZnO nanoparticles. These studies demonstrate that improved morphology control and self-assembly can increase charge transfer in hybrid materials through increased interfacial area. As an alternative route to directed ZnO nanoparticle growth, a copolymer containing pendant dipicolylamine moieties was synthesized and characterized by photophysical and electrochemical methods.Chemistr

Size and shape specific particles toward biomedical imaging: design, fabrication, and characterization

Thesis (Ph.D.)--Boston UniversityThe power of a biomedical imaging modality can be augmented and is, in large part, determined by the capabilities of the available contrast agents. For example, quantum dots represent a colorful palette of powerful contrast agents for optical fluorescence imaging and Raman spectroscopy, given their tunable multiplexing capability and long-term stability compared to traditional organic molecule-based fluorescent labels. On the contrary, as the workhorses in both clinical and research imaging, the full potentials of magnetic resonance imaging and computed tomography have yet to be actualized due to several existing fundamental limitations in the currently available contrast agents, including but not limited to, the lack of multiplexing capability, low sensitivity, as well as the lack of functional imaging capacity. Leveraging both traditional top-down micro- and nanoelectromechanical systems fabrication techniques and bottom-up self-assembly approaches, this dissertation explores the possibility of mitigating these limitations by engineering precisely controllable, size and shape (as well as a host of other materials properties) specific micro- and nanoparticles, for use as the next generation contrast agents for magnetic resonance imaging and computed tomography. Herein, the ways by which engineering approaches can impact the design, fabrication and characterization of contrast agents is investigated. Specifically, different configmations of magnetic micro- and nanoparticles, including double-disk and hollow-cylinder structmes, fabricated using a top-down approach were employed as magnetic resonance imaging contrast agents enabled with a multiplexing capability and improved sensitivity. Subsequently, a scalable nanomanufactming platform, utilizing nanoporous anodized aluminum oxide membranes as templates for pattern transfer as well as thermal/ultraviolet nanoimprinting techniques, was developed for the high throughput fabrication of size and shape specific polymeric nanorods. When ladened with X-ray attenuating tantalum oxide nanoparticle payloads, these polymeric nanorods can be used as contrast agents for computed tomography, yielding prolonged vascular circulation times, improved sensitivity, as well as targeted imaging capabilities. Furthermore, by applying various payload materials, this nanomanufacturing platform also has the flexibility to produce contrast agents for other imaging modalities, as well as the potential to realize dual-purpose agents for both diagnostic and therapeutic applications

Effect of Surfactant Architecture on Conformational Transitions of Conjugated Polyelectrolytes

Water soluble conjugated polyelectrolytes (CPEs), which fall under the category of conductive polymers, possess numerous advantages over other conductive materials for the fabrication of electronic devices. Namely, the processing of water soluble conjugated polyelectrolytes into thin film electronic devices is much less costly as compared to the processing of inorganic materials. Moreover, the handling of conjugated polyelectrolytes can be performed in a much more environmentally friendly manner than in the processing of other conjugated polymers because conjugated polyelectrolytes are water soluble, whereas other polymers will only dissolve in toxic organic solvents. The processing of electronic devices containing inorganic constituents such as copper indium gallium selenide (CIGS), is much more expensive and poses much greater environmental risks because toxic metals may be released into landfills or waterways upon cell disposal.75 Because conjugated polyelectrolytes enjoy an assortment of advantages over other materials for the manufacturing of thin film electronic devices, there is globally vested interest in the researching of their properties. Despite the fact that CPEs can serve as efficient electron transport mediums, devices such as organic solar cells cannot realize their highest efficiencies unless the morphology of CPEs is precisely controlled. Charged surfactants can electrostatically and ionically interact with CPEs, and when introduced in specific concentrations, molar ratios, and temperature ranges, will aid in a ‘coil to rod’ transition of the CPE, wherein polymer chains undergo intramolecular transitions to obtain rigid-rod morphologies. The kinetics and thermodynamics of the ‘coil to rod’ transition are heavily dependent upon the type(s) of charged surfactant complexed with the CPE (i.e. on the surfactant architecture). By performing UV/Vis Spectroscopy and Fluorometry on dilute polymer/surfactant solutions, Polarized Optical Microscopy (POM) and Small Angle X-Ray Scattering (SAXS) on high concentration polymer/surfactant solutions, and Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) on solid-state polymer/surfactant samples, the role of various surfactant architectures on the kinetics and thermodynamics of the ‘coil to rod’ transition was studied. The liquid crystalline physical properties and the extent of solid state crystallinity were also investigated. Through an analysis of the data obtained from these various techniques, it was found that the ‘coil to rod’ transition is progressively favored when the alkyl chain length of a single tailed surfactant is sequentially increased, and that as the concentration of double-tailed surfactant increases, the ‘coil to rod’ transition is negated

59th Annual Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 59th annual meeting of the Rocky Mountain Conference on Magnetic Resonance, co-endorsed by the Colorado Section of the American Chemical Society and the Society for Applied Spectroscopy. Held in Snowbird, Utah, July 22-27, 2018

Interplay between microstructure/morphology and the opto-electronic properties of materials for organic photovoltaics.

216 p.Esta tesis recoge un amplio marco de trabajo que incluye la relación microestructura-procesado-morfología-propiedades de un sistema modelo de alto rendimiento en fotovoltaica orgánica. En primer lugar, la tesis aborda las cuestiones críticas que rodean la microestructura de estado-solido de los distintos componentes de la capa activa y se relacionan dichas características con sus propiedades optoelectrónicas. A continuación, la disertación se centra en estudiar la composición de los dominios de polímero (donor) y aceptor en la morfología con separación de fases a escala nanométrica denominada heterounión volumétrica (HUV). Finalmente, el control preciso logrado sobre la microestructura de los componentes individuales y la elección astuta de los disolventes y aditivos de procesado, permite delinear el impacto de tales características en relación morfología-función del dispositivo de la celda solar. De esta manera, el trabajo mostrado en este documento amplía la percepción actual de la estructura en estado sólido de los polímeros de alto rendimiento y la relación entre la microestructura, la morfología, el procesamiento en solución y el transporte de cargas en los dispositivos más eficientes de la actualidad. Además, se establece que es necesario un conocimiento exhaustivo de las propiedades físicas inherentes de los materiales orgánicos y su microestructura en estado-solido, para poder desarrollar dispositivos óptimos y realizar una transición eficiente de la escala laboratorio hacia una escala industrial.Polyma