1,720,956 research outputs found
Architectures (co)polymères à liens covalents dynamiques
No full textDynamic covalent chemistry is an effective tool to synthetize complex architectural block (co)polymers which are difficult to achieve by conventional techniques. It permits also to develop materials that meet ecological and economic challenges (recycling, sustainability, cheap raw materials and products). In this work, we implemented imine bonds in amphiphilic comb-like copolymers and co-networks starting from PDMS with pendant amines and benzaldehyde-functionalized PEG oligomers. In a first part, we studied the properties of PDMS-r-PEG co-networks as a function of the imine crosslinking rate. The materials are flexible, little or no sticky and transparent. Thermo-mechanical analysis shows that they are micro-separated but with no long-distance order (AFM, SAXS). They can be thermally reprocessed and chemically recycled (acidic medium or in the presence of an amine), thanks to the reversible and exchangeable imine crosslinking points. In a second part, we studied the self-assembly in aqueous solution of PDMS-g-PEG comb-like copolymers with the degree of grafting of PEG chains. For a sufficient degree of grafting, the copolymers form colloidal suspensions which are stable over several months even though their shape / size change with the hydrolysis of the imine bonds. Their ability to encapsulate and release a hydrophobic compound, in single phase and in emulsion, has also been demonstrated.La chimie covalente dynamique est un outil efficace pour former des (co)polymères à blocs d’architecture complexe, difficilement atteignables par voies classiques, mais aussi développer des matériaux qui répondent aux enjeux écologiques et économiques (recyclables, réparables, bon marché). Dans ce travail, nous avons implémenté la liaison imine dans des copolymères en peigne et des co-réseaux de PDMS et PEG, par une voie "grafting to" d’oligomères PEG fonctionnalisés benzaldéhyde et d’un polymère PDMS à fonctions amines pendantes. Dans une première partie, nous avons étudié les propriétés des co-réseaux PDMS-r-PEG en fonction du taux de réticulation imine. Les matériaux sont souples, peu ou pas collants et transparents. L’analyse thermo-mécanique montre qu’ils sont micro-séparés mais sans ordre à longue distance (AFM, SAXS). Ils sont reprocessables à chaud et recyclables par voie chimique (en milieu acide ou en présence d’amine). Ces propriétés s’appuient sur la dynamique associative d’échange et la réversibilité de la liaison imine.Dans une seconde partie, nous avons étudié l’auto-assemblage en solution aqueuse des copolymères en peigne PDMS-g-PEG en fonction du taux de greffage de chaines PEG. Pour un taux de greffage suffisant, les copolymères forment des suspensions colloïdales stables sur plusieurs mois mais dont la forme/taille évolue avec l’hydrolyse des liens imines. Leur capacité à encapsuler et relarguer un composé hydrophobe, en phase simple et en émulsion, a également été démontrée
Architectures (co)polymères à liens covalents dynamiques
No full textDynamic covalent chemistry is an effective tool to synthetize complex architectural block (co)polymers which are difficult to achieve by conventional techniques. It permits also to develop materials that meet ecological and economic challenges (recycling, sustainability, cheap raw materials and products). In this work, we implemented imine bonds in amphiphilic comb-like copolymers and co-networks starting from PDMS with pendant amines and benzaldehyde-functionalized PEG oligomers. In a first part, we studied the properties of PDMS-r-PEG co-networks as a function of the imine crosslinking rate. The materials are flexible, little or no sticky and transparent. Thermo-mechanical analysis shows that they are micro-separated but with no long-distance order (AFM, SAXS). They can be thermally reprocessed and chemically recycled (acidic medium or in the presence of an amine), thanks to the reversible and exchangeable imine crosslinking points. In a second part, we studied the self-assembly in aqueous solution of PDMS-g-PEG comb-like copolymers with the degree of grafting of PEG chains. For a sufficient degree of grafting, the copolymers form colloidal suspensions which are stable over several months even though their shape / size change with the hydrolysis of the imine bonds. Their ability to encapsulate and release a hydrophobic compound, in single phase and in emulsion, has also been demonstrated.La chimie covalente dynamique est un outil efficace pour former des (co)polymères à blocs d’architecture complexe, difficilement atteignables par voies classiques, mais aussi développer des matériaux qui répondent aux enjeux écologiques et économiques (recyclables, réparables, bon marché). Dans ce travail, nous avons implémenté la liaison imine dans des copolymères en peigne et des co-réseaux de PDMS et PEG, par une voie "grafting to" d’oligomères PEG fonctionnalisés benzaldéhyde et d’un polymère PDMS à fonctions amines pendantes. Dans une première partie, nous avons étudié les propriétés des co-réseaux PDMS-r-PEG en fonction du taux de réticulation imine. Les matériaux sont souples, peu ou pas collants et transparents. L’analyse thermo-mécanique montre qu’ils sont micro-séparés mais sans ordre à longue distance (AFM, SAXS). Ils sont reprocessables à chaud et recyclables par voie chimique (en milieu acide ou en présence d’amine). Ces propriétés s’appuient sur la dynamique associative d’échange et la réversibilité de la liaison imine.Dans une seconde partie, nous avons étudié l’auto-assemblage en solution aqueuse des copolymères en peigne PDMS-g-PEG en fonction du taux de greffage de chaines PEG. Pour un taux de greffage suffisant, les copolymères forment des suspensions colloïdales stables sur plusieurs mois mais dont la forme/taille évolue avec l’hydrolyse des liens imines. Leur capacité à encapsuler et relarguer un composé hydrophobe, en phase simple et en émulsion, a également été démontrée
Copolymer architectures with dynamic covalent bonds
No full textLa chimie covalente dynamique est un outil efficace pour former des (co)polymères à blocs d’architecture complexe, difficilement atteignables par voies classiques, mais aussi développer des matériaux qui répondent aux enjeux écologiques et économiques (recyclables, réparables, bon marché). Dans ce travail, nous avons implémenté la liaison imine dans des copolymères en peigne et des co-réseaux de PDMS et PEG, par une voie "grafting to" d’oligomères PEG fonctionnalisés benzaldéhyde et d’un polymère PDMS à fonctions amines pendantes. Dans une première partie, nous avons étudié les propriétés des co-réseaux PDMS-r-PEG en fonction du taux de réticulation imine. Les matériaux sont souples, peu ou pas collants et transparents. L’analyse thermo-mécanique montre qu’ils sont micro-séparés mais sans ordre à longue distance (AFM, SAXS). Ils sont reprocessables à chaud et recyclables par voie chimique (en milieu acide ou en présence d’amine). Ces propriétés s’appuient sur la dynamique associative d’échange et la réversibilité de la liaison imine.Dans une seconde partie, nous avons étudié l’auto-assemblage en solution aqueuse des copolymères en peigne PDMS-g-PEG en fonction du taux de greffage de chaines PEG. Pour un taux de greffage suffisant, les copolymères forment des suspensions colloïdales stables sur plusieurs mois mais dont la forme/taille évolue avec l’hydrolyse des liens imines. Leur capacité à encapsuler et relarguer un composé hydrophobe, en phase simple et en émulsion, a également été démontrée.Dynamic covalent chemistry is an effective tool to synthetize complex architectural block (co)polymers which are difficult to achieve by conventional techniques. It permits also to develop materials that meet ecological and economic challenges (recycling, sustainability, cheap raw materials and products). In this work, we implemented imine bonds in amphiphilic comb-like copolymers and co-networks starting from PDMS with pendant amines and benzaldehyde-functionalized PEG oligomers. In a first part, we studied the properties of PDMS-r-PEG co-networks as a function of the imine crosslinking rate. The materials are flexible, little or no sticky and transparent. Thermo-mechanical analysis shows that they are micro-separated but with no long-distance order (AFM, SAXS). They can be thermally reprocessed and chemically recycled (acidic medium or in the presence of an amine), thanks to the reversible and exchangeable imine crosslinking points. In a second part, we studied the self-assembly in aqueous solution of PDMS-g-PEG comb-like copolymers with the degree of grafting of PEG chains. For a sufficient degree of grafting, the copolymers form colloidal suspensions which are stable over several months even though their shape / size change with the hydrolysis of the imine bonds. Their ability to encapsulate and release a hydrophobic compound, in single phase and in emulsion, has also been demonstrated
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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