1,720,968 research outputs found
Molecular rotors with aggregation-induced emission (Aie) as fluorescent probes for the control of polyurethane synthesis
Full text linkIn this work, the use of fluorescent molecular rotors such as 9-(2,2-dicyanovinyl)julolidine (DCVJ) and 2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl) phenyl)amino)phenyl)fumaronitrile (TPET-PAFN) was proposed for the real-time monitoring of polyurethane (PU) formation in a solution of dimethylacetamide starting with 4,4′-methylenediphenyl diisocyanate (MDI) and different polyethy-lene glycols (PEG400 and PEG600) as diols. Notably, relative viscosity variations were compared with fluorescence changes, recorded as a function of the polymerization progress. The agreement between these two parameters suggested the innovative use of a low-cost fluorescence detection system based on a LED/photodiode assembly directly mountable on the reaction apparatus. The general validity of the proposed experiments enabled the monitoring of polyurethane polymerization and suggested its effective applications to a variety of industrial polymers, showing viscosity enhancement during polymerization
Luminescent solar concentrators from waterborne polymer coatings
Full text linkThis study reports for the first time the use of waterborne polymers as host matrices for luminescent solar concentrators (LSCs). Notably, three types of waterborne polymer dispersions based either on acrylic acid esters and styrene (Polidisp® 7602), acrylic and methacrylic acid esters (Polidisp® 7788) or aliphatic polyester-based polyurethane (Tecfin P40) were selected as amorphous coatings over glass substrates. Water soluble Basic Yellow 40 (BY40) and Disperse Red 277 (DR277) were utilized as fluorophores and the derived thin polymer films (100 μm) were found homogeneous within the dye range of concentration investigated (0.3-2 wt. %). The optical efficiency determination (ηopt) evidenced LSCs performances close to those collected from benchmark polymethylmethacrylate (PMMA) thin films and Lumogen Red F350 (LR) with the same experimental setup. Noteworthy, maximum ηopt of 9.5 ± 0.2 were recorded for the Polidisp® 7602 matrix containing BY40, thus definitely supporting the waterborne polymer matrices for the development of high performance and cost-effective LSCs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Light-Responsive Polystyrene Films Doped with Tailored Heteroaromatic-Based Fluorophores
No full textWe describe a simple but effective strategy for imparting light-responsive peculiarity
to polystyrene films. A pH-sensitive fluorescent dye having the electron-poor pyridine nucleus as a key structural feature was synthesized and dispersed at low loadings (0.2−0.5 wt %) in a PS matrix. Once light irradiation in the near-UV range was sent to PS/dye films, PS photooxidation likely occurred at the film surface with the formation of carboxylic compounds. These species locally promoted dye protonation, thus, yielding a clear change of the film emission from blue to green.
This study opens the door to a wide range of light-responsive materials from easily accessible polymers, enabling the use of UV light as an effective trigger for smart materials and devices
Nanoporous-crystalline and amorphous films of PPO including off-on vapochromic fluorescent 7-hydroxy coumarin guests
No full textThis study examines the preparation of nanoporous-crystalline and amorphous films of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) containing 7-hydroxy coumarin (i.e., umbelliferone) for the detection of chloroform vapours. Chloroform is selected as the volatile contaminant model being considered harmful and possibly carcinogenic after prolonged exposure. Umbelliferone is chosen as a fluorescent molecule being mostly unemissive in the solid-state and apolar media. α and β nanoporous-crystalline and amorphous PPO films presenting ≈40 μm thickness have been prepared by casting from carbon tetrachloride, benzene and chloroform solutions, respectively, whereas umbelliferone inclusions (1–2 wt%) have been realized in saturated methanol mixtures. Films show fluorescence maximum at about 430 nm with very low quantum yield (ΦF) of around 1–2%, and particularly reduced in the α and β PPO films, thus suggesting stronger molecular interactions which might facilitate fluorescence self-quenching. It has demonstrated that the exposure to chloroform vapours under saturated conditions (105 ppm) turns rapidly on the fluorescence of the polymer films thanks to the solvation effect of the solvent and in agreement with the ΦF of 7% of umbelliferone in chloroform. Notably, a slower response was detected by using dichlorometane as VOC, possibly due to the weaker H-donor strength with respect to chloroform. It was worth noting, that the phenomenon results fastest for the α PPO films, i.e., in case of the lowest ΦF and quenched emission. Vapochromism appears therefore sensitive to the different fluorophore confinement, and the reported results may open new avenues for the rapid detection of VOC vapours
Polyketone-Based Anion-Exchange Membranes for Alkaline Water Electrolysis
Full text linkAnion-exchange membranes (AEMs) are involved in a wide range of applications, including fuel cells and water electrolysis. A straightforward method for the preparation of efficient AEMs consists of polymer functionalization with robust anion-exchange sites. In this work, an aliphatic polyketone was functionalized with 1-(3-aminopropyl)imidazole through the Paal-Knorr reaction, with a carbonyl (C-CO %) conversion of 33%. The anion-exchange groups were generated by the imidazole quaternization by using two different types of alkyl halides, i.e., 1,4-iodobutane and 1-iodobutane, with the aim of modulating the degree of crosslinking of the derived membrane. All of the membranes were amorphous (T-g similar to 30 degrees C), thermally resistant up to 130 degrees C, and had a minimum Young's modulus of 372 +/- 30 MPa and a maximum of 86 +/- 5 % for the elongation at break for the least-crosslinked system. The ionic conductivity of the AEMs was determined at 25 degrees C by electrochemical impedance spectroscopy (EIS), with a maximum of 9.69 mS/cm, i.e., comparable with that of 9.66 mS/cm measured using a commercially available AEM (Fumasep-PK-130). Future efforts will be directed toward increasing the robustness of these PK-based AEMs to meet all the requirements needed for their application in electrolytic cells
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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