Evolutionary Structural Optimization with Multiple Performance Constraints by Large Admissible Perturbations.

A LargE Admissible Perturbation (LEAP) with Evolutionary Structural Optimization methodology is developed. The LEAP methodology uses an incremental predictor-corrector scheme, which makes it possible to solve the redesign problem using data only from the finite element analysis of the baseline structure for changes on the order of 100% in performance and redesign variables without trial and error or repetitive finite element analyses. A structural topology evolution algorithm is introduced using a Cumulative Energy Elimination Rate (CEER) scheme by removing low energy elements at each iteration, while using the elastic modulus in each element as redesign variable in the LEAP methodology. Benchmark examples are used to demonstrate that static displacement, modal dynamic constraints, and simultaneous static and dynamic constraints can be achieved. Convergence is achieved in 3 to 7 iterations with two FEA’s per iteration inside the ESO/LEAP algorithm. Results of numerical applications satisfy engineering intuition and show the effect of multiple objectives on topology evolution.Ph.D.Mechanical Engineering and Naval Architecture and Marine EUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64710/1/earmme_1.pd

Modulation of the Physicochemical Properties of Donor–Spiro–Acceptor Derivatives through Donor Unit Planarisation: Phenylacridine versus Indoloacridine. New Hosts for Green and Blue Phosphorescent Organic Light-Emitting Diodes (PhOLEDs)

International audienceThis work reports a detailed structure–property relationship study of a series of efficient host materials based on the donor–spiro–acceptor (D-spiro-A) design for green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs). The electronic and physical effects of the indoloacridine (IA) fragment connected through a spiro bridge to different acceptor units, namely, fluorene, dioxothioxanthene or diazafluorene moiety, have been investigated in depth. The resulting host materials have been easily synthesised through short, efficient, low-cost, and highly adaptable synthetic routes by using common intermediates. The dyes possess a very high triplet energy (ET) and tuneable HOMO/LUMO levels, depending on the strength of the donor/acceptor combination. The peculiar electrochemical and optical properties of the IA moiety have been investigated though a fine comparison with their phenylacridine counterparts to study the influence of planarisation. Finally, these molecules have been incorporated as hosts in green and sky-blue PhOLEDs. For the derivative SIA-TXO2 as a host, external quantum efficiencies as high as 23 and 14 % have been obtained for green and sky-blue PhOLEDs, respectively

Comparison of the Morphology Development of Polymer-Fullerene and Polymer-Polymer Solar Cells during Solution-Shearing Blade Coating

In this work, the detailed morphology studies of polymer poly(3‐hexylthiophene‐2,5‐diyl) (P3HT):fullerene(PCBM) and polymer(P3HT):polymer naphthalene diimide thiophene (PNDIT) solar cell are presented to understand the challenge for getting high performance all‐polymer solar cells. The in situ X‐ray scattering and optical interferometry and ex situ hard and soft X‐ray scattering and imaging techniques are used to characterize the bulk heterojunction (BHJ) ink during drying and in dried state. The crystallization of P3HT polymers in P3HT:PCBM bulk heterojunction shows very different behavior compared to that of P3HT:PNDIT BHJ due to different mobilities of P3HT in the donor:acceptor glass. Supplemented by the ex situ grazing incidence X‐ray diffraction and soft X‐ray scattering, PNDIT has a lower tendency to form a mixed phase with P3HT than PCBM, which may be the key to inhibit the donor polymer crystallization process, thus creating preferred small phase separation between the donor and acceptor polymer

Studies of Solution-Processed Organic Light-Emitting Diodes and All-Polymer Solar Cells

Thesis (Ph.D.)--University of Washington, 2014Organic electronics, commonly referred as plastic electronics, is an emerging technology for addressing many challenges that our society is facing. Over the past two decades, organic electronics has gained enormous attention due to its many advantages, including low power consumption, low-cost, scalable, and flexible design. Development of high-performance devices by designing new materials and related device engineering is crucial to the future advances in organic electronics. This dissertation focuses on studies of two classes of optoelectronic devices, organic light-emitting diodes (OLEDs) and all-polymer solar cells, fabricated by solution-processing of organic semiconductors, and aims to better understand structure-property-performance relationships resulting from solution-based fabrication. Study of bisindenoanthrazolines and dendritic oligoquinolines were found to be promising new electron-transport materials (ETMs) for high-performance phosphorescent OLEDs (PhOLEDs). Solution-processed multilayered blue PhOLEDs with orthogonal solution-processed ETMs were found to have the highest efficiency (luminous efficiency = 28.3 cd/A and external quantum efficiency = 15.5 %) observed to date among polymer-based devices. The surface morphology and charge-transport properties of the ETMs were successfully tuned by solution-deposition, which made it possible to eliminate the need for interfacial materials and low work function metals commonly used as cathode materials in OLEDs. High-performance solution-processed PhOLEDs using commercial ETMs were also demonstrated using orthogonal solution-processing. The bulk conductivity and charge transport properties of ETMs were enhanced by a novel solution n-doping with alkali metal salts. Sulfone- and dibenzosuberane-based materials were demonstrated as promising new classes of ETMs that possess high triplet energies (> 2.8 - 3.0 eV). Multilayered PhOLEDs with a solution-processed blue triplet emission layer using high triplet energy ETMs as an electron-transport layer were found to have significantly improved performance, including high current efficiency and external quantum efficiency (~ 20 %). Finally, solution-processed polymer/polymer blend solar cells using new naphthalene diimide-based acceptor copolymers were investigated and found to be the most efficient all-polymer solar cells reported to date. Controlling polymer blend morphology by solution-processing from a co-solvent system also led to further enhancement of device performance

Interfacial study of polyimide/copper system using silane-modified polyvinylimidazoles as adhesion promoters

Polyvinylimidazoles(PVIs) modi®ed with vinyltrimethoxysilane (VTS) in different mole ratios were applied as adhesion promoters for polyimide (PI)/copper interface. The effects of the composition of VTS-modi®ed PVI copolymers on lap shear strengths between PI and copper were investigated at different bonding temperatures. Fourier transform infrared spectroscopy was applied to examine the thermooxidative degradation of PI and oxidation of copper. In addition, scanning electron microscope and contact angle measurement analysis were performed to investigate the compatibility of VTS-modi®ed PVIs with PI. An improvement in interfacial adhesion strength was obtained using the adhesion promoters. Especially at higher bonding temperatures, a signi®cant increment in lap shear strength was seen when the mole ratio (VI:VTS) was 3:7, due to the high thermal stability of the silane unit. However, at lower bonding temperatures, lap shear strength does not increase as above, owing to the poor compatibility between the VTS-modi®ed PVI with PI. q 2001 Elsevier Science Ltd. All rights reserved.This research has been carried out by Research Institute of Engineering Science (RIES) and the authors gratefully acknowledge the research support of RIES

Calculations of Surface Stresses in Metals Under Mechanical Strains

We calculate the variation of the surface stresses according to uniaxial and biaxial strains in face-centered cubic (FCC) metals. In our study, three mainly observed free surfaces of seven representative FCC metals are considered. Employed method is molecular mechanics, in which the interaction of atoms is described by empirical interatomic potentials. As uniaxial strain increases to tensile direction, the surface stresses on {100} and {110} free surfaces decrease monotonously, while those on {111} surface increase. These tendencies are the same regardless of the species of metals and interatomic potentials employed. However, when the system is under biaxial strain, surface stresses change different according to the surface directions, the species of metals, and even interatomic potentials. On {100) and {111} surfaces, heavy metals (Pt, Au) show the opposite variation to light metals (Ni, Cu). In the cases of Pd and Ag, the surface stresses reveal the opposite tendency, depending on interatomic potentials used.close