Confinement and Interface Effects in Self Assembly of Functional Block Copolymers

Functional block copolymers are of increasing interest for their ability to combine the functional properties of one polymer, such as a polymer electrolyte or semiconductor, with the mechanical properties of another polymer. Balancing properties in this way can be challenging, however, due to the complex relationship between self-assembled morphology and resulting properties. Interface effects in particular, whether due to confinement within a self-assembled domain or at macroscopic boundary, are poorly understood in such functional block copolymers. This dissertation consists of two main thrusts, each investigating confinement or interfacial effects in a different functional block copolymer system. The first thrust focuses on the relationship between crystallization and self-assembly in diblock block copolymers of poly(3-dodecylthiophene) (P3DDT) and poly(2-vinylpyridine) (P2VP). Through the use of in-situ and time-resolved X-ray scattering, three distinct modes of P3DDT crystallization were observed. These modes were found to depend on both the degree of crystallinity of the P3DDT block as well as the morphology of the block copolymer. Since degree of crystallization in these materials can, in many cases, be tuned without impacting self-assembled morphology (and vice-versa), these findings demonstrate that in this system the parameters that govern classical block copolymer self-assembly are decoupled from those that govern crystallization. In the second thrust, the impact of interfacial order on the ionic conductivity in block copolymers of polystyrene (PS) and a polymeric ionic liquid (PIL) is investigated. Through a combination of X-ray scattering, impedance spectroscopy, and island and holes studies on thin films, it was found that the formation of highly-oriented lamellar layers at film interfaces, which results in significant anisotropy in the ionic conductivity of PS-PIL block copolymers. In-plane conductivity was found to be enhanced in these materials by as much as 18x compared to the through-plane conductivity. Interestingly, a similar phenomenon was observed in a random copolymer of styrene and ionic liquid, with in-plane conductivity enhanced by as much as 3x compared to the through-plane conductivity. This suggests that interfacial reordering even at very small length scales, which has been observed in amphiphilic random copolymers with large pendant groups, is sufficient to produce significant anisotropy in the ionic conductivity of the film

Analysis combining correlated glaucoma traits identifies five new risk loci for open-angle glaucoma

Open-angle glaucoma (OAG) is a major cause of blindness worldwide. To identify new risk loci for OAG, we performed a genome-wide association study in 3,071 OAG cases and 6,750 unscreened controls, and meta-analysed the results with GWAS data for intraocular pressure (IOP) and optic disc parameters (the overall meta-analysis sample size varying between 32,000 to 48,000 participants), which are glaucoma-related traits. We identified and independently validated four novel genome-wide significant associations within or near MYOF and CYP26A1, LINC02052 and CRYGS, LMX1B, and LMO7 using single variant tests, one additional locus (C9) using gene-based tests, and two genetic pathways - “response to fluid shear stress” and “abnormal retina morphology” - in pathway-based tests. Interestingly, some of the new risk loci contribute to risk of other genetically-correlated eye diseases including myopia and age-related macular degeneration. To our knowledge, this study is the first integrative study to combine genetic data from OAG and its correlated traits to identify new risk variants and genetic pathways, highlighting the future potential of combining genetic data from genetically-correlated eye traits for the purpose of gene discovery and mapping

Genomic investigations of unexplained acute hepatitis in children

Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children

Computational Design of Cyclic Nitroxides as Efficient Redox Mediators for Dye-Sensitized Solar Cells

Cyclic nitroxide radicals represent promising alternatives to the iodine-based redox mediator commonly used in dye-sensitized solar cells (DSSCs). To date DSSCs with nitroxide-based redox mediators have achieved energy conversion efficiencies of just over 5 % but efficiencies of over 15 % might be achievable, given an appropriate mediator. The efficacy of the mediator depends upon two main factors: it must reversibly undergo one-electron oxidation and it must possess an oxidation potential in a range of 0.600-0.850 V (vs. a standard hydrogen electrode (SHE) in acetonitrile at 25 °C). Herein, we have examined the effect that structural modifications have on the value of the oxidation potential of cyclic nitroxides as well as the reversibility of the oxidation process. These included alterations to the N-containing skeleton (pyrrolidine, piperidine, isoindoline, azaphenalene, etc.), as well as the introduction of different substituents (alkyl-, methoxy-, amino-, carboxy-, etc.) to the ring. Standard oxidation potentials were calculated using high-level ab initio methodology that was demonstrated to be very accurate (with a mean absolute deviation from experimental values of only 16 mV). An optimal value of 1.45 for the electrostatic scaling factor for UAKS radii in acetonitrile solution was obtained. Established trends in the values of oxidation potentials were used to guide molecular design of stable nitroxides with desired E°ox and a number of compounds were suggested for potential use as enhanced redox mediators in DSSCs

Reductive alkylation of beta-alkoxy aziridines:new route to substituted allylic amines

A new route to substituted cyclic allylic amines via the reductive alkylation of beta-alkoxy aziridines using excess alkyllithium reagents is described

Computational design of cyclic nitroxides as efficient redox mediators for dye-sensitized solar cells

Cyclic nitroxide radicals represent promising alternatives to the iodine-based redox mediator commonly used in dye-sensitized solar cells (DSSCs). To date DSSCs with nitroxide-based redox mediators have achieved energy conversion efficiencies of just over 5 % but efficiencies of over 15 % might be achievable, given an appropriate mediator. The efficacy of the mediator depends upon two main factors: it must reversibly undergo one-electron oxidation and it must possess an oxidation potential in a range of 0.600-0.850 V (vs. a standard hydrogen electrode (SHE) in acetonitrile at 25 °C). Herein, we have examined the effect that structural modifications have on the value of the oxidation potential of cyclic nitroxides as well as the reversibility of the oxidation process. These included alterations to the N-containing skeleton (pyrrolidine, piperidine, isoindoline, azaphenalene, etc.), as well as the introduction of different substituents (alkyl-, methoxy-, amino-, carboxy-, etc.) to the ring. Standard oxidation potentials were calculated using high-level ab initio methodology that was demonstrated to be very accurate (with a mean absolute deviation from experimental values of only 16 mV). An optimal value of 1.45 for the electrostatic scaling factor for UAKS radii in acetonitrile solution was obtained. Established trends in the values of oxidation potentials were used to guide molecular design of stable nitroxides with desired E° ox and a number of compounds were suggested for potential use as enhanced redox mediators in DSSCs. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Gaze behavior among experts and trainees during optic disc examination : does how we look affect what we see?

Purpose. The authors compared the visual gaze behaviors of glaucoma subspecialists with those of ophthalmology trainees during optic disc and retinal nerve fiber layer (RNFL) examination.Methods. Seven glaucoma subspecialists and 23 ophthalmology trainees participated in the project. Participants were shown eight glaucomatous optic disc images with varied morphology. Eye movements during examination of the optic disc photographs were tracked. For each disc image, graders were asked to assign a presumptive diagnosis for probability of glaucoma. There was no time restriction.Results. Overall, trainees spent more time looking at disc images than glaucoma subspecialists (21.3 [13.9&ndash;37.7] vs. 16.6 [12.7&ndash;19.7]) seconds; median [interquartile range (IQR)], respectively; P &lt; 0.01) and had no systematic patterns of gaze behavior, and gaze behavior was unaltered by disc morphology or topographic cues of pathology. Experienced viewers demonstrated more systematic and ordered gaze behavior patterns and spent longer times observing areas with the greatest likelihood of pathology (superior and inferior poles of the optic nerve head and adjacent RNFL) compared with the trainees. For discs with focal pathology, the proportion of total time spent examining definite areas of pathology was 28.9% (22.4%&ndash;33.6%) for glaucoma subspecialists and 13.5% (12.2%&ndash;19.2%) for trainees (median [IQR]; P &lt; 0.05). Furthermore, experts adapted their viewing habits according to disc morphology.Conclusions. Glaucoma subspecialists adopt systematic gaze behavior when examining the optic nerve and RNFL, whereas trainees do not. It remains to be elucidated whether incorporating systematic viewing behavior of the optic disc and RNFL into teaching programs for trainees may expedite their acquisition of accurate and efficient glaucoma diagnosis skills.<br /

Domain Structures of Poly(3-dodecylthiophene)-Based Block Copolymers Depend on Regioregularity

Microphase-separation behavior of conjugated–amorphous block copolymers (BCPs) is driven by a complex interplay between Flory–Huggins interaction (χ), liquid crystalline (LC) interaction, and crystallization. Herein, in order to elucidate the influence of LC interaction on the morphology of the BCPs, we report the effects of regioregularity (RR) on the microphase separation and molecular packing structures of poly­(3-dodecyl­thiophene)-<i>block</i>-poly­(2-vinyl­pyridine) (P3DDT-<i>b</i>-P2VP). To decouple the effect of LC interactions from crystallization kinetics, we investigate the morphological behavior of the P3DDT-<i>b</i>-P2VP at above the melting temperature of P3DDT (∼160 °C). Both electron microscopy and X-ray scattering show an abrupt reduction in the domain spacing of both lamellar and cylindrical phases as the RR of P3DDT block increases. Specifically, lower RR (i.e., 85, 79, and 70%) BCPs have larger domain spacings than high RR (94%) by 50% (lamellar) or 80% (cylindrical), even though the overall molecular weights and P2VP volume fractions were similar for each RR. We propose that the RR-driven transition in domain spacing is caused by a change in P3DDT conformations and interchain interactions. When RR is low, the system assembles into a typical bilayer structure like other semiflexible and flexible block copolymer systems. When RR is high, the less flexible P3DDT chains are extended, driving their assembly into an LC monolayer. Significantly, this study demonstrates that tunable RR provides a simple route to manipulate melt state self-assembly of conjugated–amorphous materials