1,721,026 research outputs found
New experimental evidence supporting the mesoscopic segregation model in room temperature ionic liquids
No full textThe existence of a high degree of order over the mesoscopic spatial scale in room temperature ionic liquids is one of their most intriguing properties. Recently the possibility that such a feature, that is witnessed by the occurrence of peculiar low Q diffraction features, reflects nm-scale structural organization has been questioned on the basis of both experimental and computational studies. In this contribution we discuss these studies and present novel experimental evidence that confirm the existence of nm-scale spatial heterogeneities due to the segregation of apolar moieties dispersed in a polar network. The consequence of this scenario is that when the chain polarity gets closer to that of the charged head, the structural heterogeneities are no longer observed
Amphiphile Meets Amphiphile: Beyond the Polar-Apolar Dualism in Ionic Liquid/Alcohol Mixtures
No full textThe mesoscopic morphology of binary mixtures of ethylammonium nitrate (EAN), the protic ionic liquid par excellence, and methanol is explored using neutron/X-ray diffraction and computational techniques. Both compounds are amphiphilic and characterized by an extended hydrogen bonding network: surprisingly, though macroscopically homogeneous, these mixtures turn out to be mesoscopically highly heterogeneous. Our study reveals that even in methanol-rich mixtures, a wide distribution of clusters exists where EAN preserves its bulk, sponge-like morphology. Accordingly methanol does not succeed in fully dissociating the ionic liquid that keeps on organizing in a bulk-like fashion. This behavior represents the premises to the more dramatic phenomenology observed with longer alcohols that eventually phase separate from EAN. These results challenge the commonly accepted polar and apolar moieties segregation in ionic liquids/molecular liquids mixtures and the current understanding of technologically relevant solvation processes.The mesoscopic morphology of binary mixtures of ethylammonium nitrate (EAN), the protic ionic liquid par excellence, and methanol is explored using neutron/X-ray diffraction and computational techniques. Both compounds are amphiphilic and characterized by an extended hydrogen bonding network: surprisingly, though macroscopically homogeneous, these mixtures turn out to be mesoscopically highly heterogeneous. Our study reveals that even in methanol-rich mixtures, a wide distribution of clusters exists where EAN preserves its bulk, sponge-like morphology. Accordingly methanol does not succeed in fully dissociating the ionic liquid that keeps on organizing in a bulk-like fashion. This behavior represents the premises to the more dramatic phenomenology observed with longer alcohols that eventually phase separate from EAN. These results challenge the commonly accepted polar and apolar moieties segregation in ionic liquids/molecular liquids mixtures and the current understanding of technologically relevant solvation processe
Structural organization and phase behaviour of 1-butyl-3-methylimidazolium hexafluorophosphate: an high pressure Raman spectroscopy study
No full textThe complexity of the phase diagram of a representative room temperature ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6]) is explored by means of Raman spectroscopy at high pressure (up to 1000 MPa) and high temperature (from room temperature to 100 degrees C) conditions. The first experimental evidence of the existence of a second crystalline phase for this salt at high pressure conditions is provided. By comparing the low frequency vibrational bands for the liquid state and the two observed crystalline phases, we confirm the scenario that considers the crystal polymorphism in this class of materials as a consequence of the rotational isomerism of the butyl chain. Furthermore the pressure dependence of other vibrational bands indicates the existence of a structural rearrangement across p approximate to 50 MPa at ambient temperature
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
Structural Organization in Neat Ionic Liquids and in Their Mixtures
No full textRoom temperature ionic liquids (RTILs) represent a class of materials whose employment in several applications is considered as a green alternative to toxic chemicals. Their potentialities are deemed to grow the more we understand their chemical-physical behaviour. As a matter of fact properties as basic as structural organization or microscopic interactions turn out to play a major role in many of their chemical-physical features, such as diffusive properties or solvation capabilities. Their being complex solvent media is a direct consequence of the chemical composition that leads to as diverse interactions as dispersive, coulombic, H-bonding, just to mention the most commonly encountered in conventional RTILs. The degree of comprehension of the structure in neat and mixed RTILs is steadily growing thank to the use of several complementary techniques such as diffraction and spectroscopic techniques and the link between their chemical details and the structure at microscopic as well as mesoscopic level is being unravelled by these studies. That opens the way to the rationalisation not only of basic chemical-physical properties but also of their bulk performances as solvent media. In this contribution we present experimental results aiming provide a structural description of two classes of samples. A first selection of diffraction experiments will aim to address the now well-known issue of mesoscopic structural organization in medium chain length RTILs. We will report original diffraction data from the family of 1-alkyl,3-methylimidazolium tetrafluoroborate as a function of the side alkyl chain length, highlighting the role of this parameter in affecting the mesoscopic order in the neat RTIL. We will also show experimental data highlighting the role of polar versus apolar interactions in determining this phenomenology describing results from a sample whose side chain is not an alkyl one. In the second part of this contribution, experimental results will be reported on binary mixtures of selected tetrafluoroborate salts and water. By the use of complementary techniques such as Raman and infrared spectroscopies, X-Ray and neutron diffraction we will provide a detailed overview of the phase diagram, nature of interactions as well as structural properties of these binary mixtures, expanding the current level of description for these systems. Overall we aim to provide a description of how the proposed experimental techniques can be successfully used to provide useful information in exploring the exciting, complex issue of RTILs and their mixtures
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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