1,721,033 research outputs found
Local order in protic ionic liquid/methanol mixtures
No full textProtic ionic liquids (PILs), such as ethylammonium nitrate (EAN), are ionic compounds with low melting point that
are prepared by combination of a Brønsted acid and base. As such they are characterised by the presence of protondonor
and -acceptor sites, which contribute to develop a hydrogen-bonded network. Moreover, in the case of EAN,
distinct mesoscopic order exists as a consequence of its inherent amphiphilicity. Such a structural complexity is
deemed to increase upon mixing with another H-bonding active compound, such as methanol.
In this presentation we will show the results from a study conducted taking advantage of the high complementarity
of x-ray and neutron scattering, to probe the mesoscopic structure. The local order of these mixtures will also be
investigated using Raman and IR spectroscopy data, to monitor the structural changes as a function of both
concentration and temperatureProtic ionic liquids (PILs), such as ethylammonium nitrate (EAN), are ionic compounds with low melting point that
are prepared by combination of a Brønsted acid and base. As such they are characterised by the presence of protondonor
and -acceptor sites, which contribute to develop a hydrogen-bonded network. Moreover, in the case of EAN,
distinct mesoscopic order exists as a consequence of its inherent amphiphilicity. Such a structural complexity is
deemed to increase upon mixing with another H-bonding active compound, such as methanol.
In this presentation we will show the results from a study conducted taking advantage of the high complementarity
of x-ray and neutron scattering, to probe the mesoscopic structure. The local order of these mixtures will also be
investigated using Raman and IR spectroscopy data, to monitor the structural changes as a function of both
concentration and temperatur
Synthesis and small and wide angle x-ray scattering characterization of L-proline based chiral ionic liquids
No full textIn this work we report the first small and wide-angle X-Ray diffraction study (S-WAXS) of L-proline ester based ionic liquids, a family of chiral ionic liquids (CILs) with several potential useful applications. Along the synthetic pathway that was followed to obtain the already described systems in ultra-pure form, some new compounds were synthesized. Noteworthy differences were observed in the SAXS low Q peak positions trends between chloride and nitrate salts. © 2015 Bentham Science Publishers
Communication: Anion-specific response of mesoscopic organization in ionic liquids upon pressurization
No full textOne of the outstanding features of ionic liquids is their inherently hierarchical structural organization at mesoscopic spatial scales. Recently experimental and computational studies showed the fading of this feature when pressurising. Here we use simulations to show that this effect is not general: appropriate anion choice leads to an obstinate resistance against pressurization
Solubility and solvation features of native cyclodextrins in 1-ethyl-3-methylimidazolium acetate
Full text linkThe comprehension of the mechanism entailing efficient solvation of cyclodextrins (CD) by green solvents is of great relevance to boost environmentally sustainable usages of smart supramolecular systems. Here, 1-ethyl-3- methylimidazolium acetate, an ecofriendly ionic liquid (IL), is considered as an excellent solvent for native CDs. This IL efficiently dissolves up to 40 wt.% β- and γ-CD already at ambient temperature and X-ray scattering indicates that CDs do not tend to detrimental flocculation under these drastic concentration conditions. Simu- lation techniques reveal the intimate mechanism of CD solvation by the ionic species: while the strong hydrogen bonding acceptor acetate anion interacts with CD's hydroxyl groups, the imidazolium cation efficiently solvates the hydrophobic CD walls via dispersive interactions, thus hampering CD's hydrophobic driven flocking. Overall the amphiphilic nature of the proposed IL provides an excellent solvation environment for CDs, through the synergic action of its components
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
Liquid structure of a choline chloride-water natural deep eutectic solvent: A molecular dynamics characterization
Full text linkThe liquid structure of a representative of the first water-in-salt (WiS) Natural Deep Eutectic Solvents (NADES), hereinafter indicated as aquoline, a mixture of choline chloride (ChCl) and water with molar ratio 1:3.33, is ex- plored at ambient conditions. Using Molecular Dynamics (MD) simulation tools, we extract structural informa- tion at atomistic level on the nature of inter-correlations between the different moieties. Despite being a very fluid liquid, with much lower viscosity than other common ChCl-based DES, aquoline turns out to be very struc- tured. Computed X-ray and neutron weighted scattering patterns (the latter also on selectively deuterated mix- tures) highlight the existence of mesoscopic organization that is rationalised in terms of choline vs. water/ chloride structural alternation. The study shows that choline cations are highly coordinating the surrounding en- vironment: strong hydrogen bonding mediated correlations between the hydroxyl group and water or chloride are detected. In addition, the ammonium group drives the formation of a complex solvating environment, with water, chloride and hydroxyl moieties approaching it, between the hindering methyl groups. Strong hydrogen- bonding interactions between water molecules and between water and anions are detected and, while water cannot create a bulk water-like environment around itself, its network with neighbour water or anions develops long chains across the bulk phase. This is a first study that will be extended based on complementary experimen- tal work as a function of water content and temperature/pressure, to explore structural and dynamic properties of this class of materials
Exploring macro- and microscopic features of binary L-menthol/xylenol isomers mixtures: An integrated experimental and computational investigation
Full text linkThe complex nature of hydrogen bonding interactions in cyclohexyl-phenolic alcohols mixtures motivates investigations of their distinctive characteristics. To this end, we explored macroscopic bulk properties and microscopic features of four binary eutectic mixtures formed by mixing each of the four 2,n-dimethyl phenol (xylenol) isomers (n = 3, 4, 5, 6) and (1R,2S,5R)-2-Isopropyl-5-methylcyclohexanol (L-menthol). The density and viscosity of the mixtures were measured over a wide temperature and composition range. It was found that 2,n-xylenol isomers are denser than L-menthol, and the density of the mixtures decreased with increasing L-menthol mole fraction. L-menthol/2,3-xylenol showed the highest density among the studied mixtures. The larger density of L-menthol/2,3-xylenol was attributed to the negative excess molar volume. On the other hand, 2,n-xylenol isomers are less viscous than L-menthol, and the viscosity of the mixture increased with increasing L-menthol mole fraction. The viscosity of L-menthol/2,3-xylenol, L-menthol/2,4-xylenol, and L-menthol/2,5-xylenol was very similar, while L-menthol/2,6-xylenol showed significantly lower viscosity. This experimental work was complemented with molecular dynamics (MD) simulations on all mixtures with an L-menthol mole fraction of 0.6. The atomistic insight into intermolecular structural correlations provided by MD simulations allows for extracting useful information on the nature of close-neighbor interactions. Analysis of MD simulations allows for highlighting the role of hydrogen bonding interactions and dispersive ones (including aromatic effects) on driving local organization and suggesting potential structural explanations for the experimental observations
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