Structure and dynamics of a confined ionic liquid. topics of relevance to dye-sensitized solar cells

The behavior of a model ionic liquid (IL) confined between two flat parallel walls was studied at various interwall distances using computer simulations. The results focus both on structural and dynamical properties. Mass and charge density along the confinement axis reveal a structure of layers parallel to the walls that leads to an oscillatory profile in the electrostatic potential. Orientational correlation functions indicate that cations at the interface orient tilted with respect to the surface and that any other orientational order is lost thereafter. The diffusion coefficients of the ions exhibit a maximum as a function of the confinement distance, a behavior that results from a combination of the structure of the liquid as a whole and a faster molecular motion in the vicinity of the walls. We discuss the relevance of the present results and elaborate on topics that need further attention regarding the effects of ILs in the functioning of IL-based dye-sensitized solar cells.

Simulation of interfaces between room temperature ionic liquids and other liquids

The structure and properties of the interfaces between the room temperature ionic liquid dimethylimidazolium chloride ([dmim]Cl) and different Lennard-Jones fluids and between ionic liquid and water have been studied by molecular dynamics simulations, and compared to the ionic liquid-vapour interface. Two contrasting types of interface were investigated, thermodynamically stable interfaces between ionic liquid and vapour and between ionic liquid and Lennard-Jones fluids, and diffusing interfaces between miscible phases of different compositions involving water. The density profiles of different species through the interface are presented. The cations and water molecules near the former type of interface are aligned relative to the surface, but no orientational preference was found near or in the broad diffusing interface. The ionic liquid has a negative electrostatic potential relative to vapour or Lennard-Jones fluid, but is more positive than pure water. This contrast is explained in terms of the relative importance of orientation and concentration differences in the two types of interface.

Local and semilocal density functional computations for crystals of 1-alkyl-3-methyl-imidazolium salts

The accuracy and reliability of popular density functional approximations for the compounds giving origin to room temperature ionic liquids have been assessed by computing the T=0 K crystal structure of several 1-alkyl-3-methyl-imidazolium salts. Two prototypical exchange-correlation approximations have been considered, i.e., the local density approximation (LDA) and one gradient corrected scheme [PBE-GGA, Phys. Rev. Lett. 77, 3865 (1996)]. Comparison with low-temperature x-ray diffraction data shows that the equilibrium volume predicted by either approximations is affected by large errors, nearly equal in magnitude (~10%), and of opposite sign. In both cases the error can be traced to a poor description of the intermolecular interactions, while the intramolecular structure is fairly well reproduced by LDA and PBE-GGA. The PBE-GGA optimization of atomic positions within the experimental unit cell provides results in good agreement with the x-ray structure. The correct system volume can also be restored by supplementing PBE-GGA with empirical dispersion terms reproducing the r-6 attractive tail of the van der Waals interactions.

Ion Association in [bmim][PF6]/Naphthalene Mixtures: An Experimental and Computational Study

Mixtures of room temperature ionic liquids (IL) with neutral organic molecules provide a valuable testing ground to investigate the interplay of the ionic and molecular-dipolar state in dense Coulomb systems at near ambient conditions. In the present study, the viscosity eta and the ionic conductivity a of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])/naphthalene mixtures at T = 80 degrees C have been measured at 10 stoichiometries spanning the composition range from pure naphthalene to pure [bmim][PF6]. The viscosity grows nearly monotonically with increasing IL mole fraction (x), whereas the conductivity per ion displays a clear peak at x approximate to 15%. The origin of this maximum has been investigated using molecular dynamics simulations based on a classical force field. Snapshots of the simulated samples show that the conductivity maximum is due to the gradual transition in the IL component from an ionic state at high x to a dipolar fluid made of neutral ion pairs at low x. At concentrations x <0.20 the ion pairs condense into molecular-thin filaments bound by dipolar forces and extending in between nanometric droplets of IL. These results are confirmed and complemented by the computation of dynamic and transport properties in [bmim][PF6]/naphthalene mixtures at low IL concentration.

Clusters, liquids and crystals of dialkylimidazolium salts. A combined perspective from ab initio computer simulations

We summarize results obtained by a combination of ab initio and classical computer simulations of dialkylimidazolium ionic liquids in different states of aggregation, from crystals to liquids and clusters. Unusual features arising from the competition between electrostatic, dispersion, and hydrogen-bonding interactions are identified at the origin of observed structural patterns. We also discuss the way Brønsted acids interact with ionic liquids leading to the formation of hydrogen-bonded anions.

Entre la "flânerie" y el ostracismo: la resignificación subjetiva de la ciudad en Fabián Casas y Martín Gambarotta

Desde los estudios pioneros de Walter Benjamín dedicados a la imagen del flâneur en la poesía de Baudelaire, la experiencia del sujeto poético y su íntima reconstrucción afectiva de la ciudad constituyen un índice significativo para aproximarnos a la experiencia de la vida moderna. En este artículo, nos interesa revisar cuáles son las particularidades que distinguen esta experiencia en un corpus de poesía argentina reciente -los libros Punctum y Refrito, de Martín Gambarotta, y Horla City y otros, de Fabián Casas-, que durante las décadas de 1990 y 2000 tematiza, con insistencia y mediante opciones diversas, la relación sujeto-ciudad. En dichos textos, es posible releer una continuidad -relativamente canónicadel paseante por los márgenes periféricos de la modernidad -en el caso de Casas- y la reclusión voluntaria, como repliegue extremo ante la vivencia del deambular callejero, que se percibe como intimidante en Gambarotta.

Arquetipo y homofobia en el relato mexicano de temática gay

En este trabajo se pretende analizar cómo autores de diversas generaciones han contribuido al arraigo en el inconsciente colectivo, y en la misma literatura, a fijar valores y juicios predeterminados por los dogmas religiosos e ideologías de las instituciones gubernamentales. Para poder entender la evolución de los patrones del arquetipo y la homofobia, el análisis se realizará tomando en cuenta el orden cronológico en que se suceden los relatos, que van de la Revolución al término de la primera década del nuevo siglo, es decir cien años. También se analizarán los tratamientos estéticos y narrativos en los relatos.

Recepción e influencia de la literatura hispanoamericana en Corea

A medida que el concepto de "nación" se ha debilitado en estos últimos años, y de forma muy rápida, el límite convencional de la cultura se está desvaneciendo y el mundo se mueve hacia un orden cultural integrado, a través de intercambios constantes entre las culturas, a pesar de las barreras discriminatorias. La literatura, en este sentido, no es una excepción y es necesario discutir la relación entre la literatura coreana y la hispanoamericana desde la perspectiva de la literatura comparativa. El presente estudio ofrece una mirada más cercana al proceso y a los distintos aspectos del modo en que las obras de los escritores hispanoamericanos han sido aceptadas en Corea del Sur. La literatura hispanoamericana se ha introducido en Corea desde principios del siglo XX y se extendió rápidamente a partir de los ochenta, cuando la controversia literaria del posmodernismo se desató y las obras de Borges y García Márquez fueron presentadas a los lectores coreanos. Sería interesante examinar los aspectos sobre cómo los escritores hispanoamericanos como Neruda, Borges y García Márquez se han integrado en la literatura coreana. En esta etapa, sin embargo, es difícil determinar si su influencia es suficientemente permanente como para convertirse en un linaje, o simplemente se trata de un fenómeno temporal. No obstante, la literatura hispanoamericana seguirá expandiendo interrelaciones crecientes con la coreana más allá de las fronteras, ejerciendo una gran influencia entre sí.

Leopoldo Panero and his antology of the Spanish American Poetry. A “personal” reading of America

El presente artículo trata de ofrecer una lectura estética y política de la Antología de la poesía hispanoamericana que publicara Leopoldo Panero entre 1944 y 1945 bajo protección gubernamental. Para ello se parte de la particular biografía del escritor astorgano, su relación en los años treinta con los poetas hispanoamericanos –especialmente Vallejo y Neruda– y su gira por América ya como supuesto prohombre del régimen franquista en 1949 y 1954. La lectura sistemática de sus prólogos y selección de poetas revela la particular visión de Panero sobre Hispanoamérica, mediatizada por el concepto imperial de Falange pero formulada bajo su propia visión de lo que la lírica americana representa para la lengua castellana. Se sostiene así en estas líneas la tesis de que los postulados de Panero representan, a pesar de todo, una opción mucho más compleja de lo que se suele considerar.

Vuelta a lo que resultó un comienzo: de géneros literarios y política en “Simbiosis”, de Rodolfo Walsh

“Simbiosis”, aparecido originalmente en 1956, constituye la instancia inicial de la serie de cuentos policiales de Rodolfo Walsh que, extendida hasta 1962, protagonizan Daniel Hernández y el comisario Laurenzi. Pero “Simbiosis” representa, además, un momento de rupturas en la trayectoria de Walsh, rupturas observables a la luz de su obra previa, y que contribuyen a definir la singular posición que el escritor procura adoptar en el campo literario de la época. En la nacionalización del género policial que propone, el cuento a la vez recupera y cuestiona el canon clásico del género, al adoptar motivos de la literatura fantástica cuya operatividad como explicaciones de un delito se asocia a su origen en el saber popular, saber al cual Laurenzi accede como comisario de pueblo. Correlativamente, la equívoca resolución del crimen, debatida entre dos matrices de género, una racional y otra sobrenatural, así como el interrogante sobre la culpabilidad que deja abierto el relato, son resonancias significativas de su contexto histórico, desatendidas aún por la crítica: se trata, en particular, de los debates sobre culpables e inocentes políticos que inició en 1955 el derrocamiento militar del gobierno peronista.

Interaction of Room Temperature Ionic Liquid Solutions with a Cholesterol Bilayer

Water solutions of representative (IC(4)mim][Cl] and [C(4)mim][Tf2N] room temperature ionic liquids (ILs) in contact with a neutral lipid bilayer made of cholesterol molecules has been investigated by molecular dynamics simulations based on an empirical force field model. The results show that both ILs display selective adsorption at the water-cholesterol interface, with partial inclusion of ions into the bilayer. In the case Of [C(4)mim][Cl], the adsorption of ions at the water-cholesterol interface is limited by a sizable bulk solubility of the IL, driven by the high water affinity of [Cl](-). The relatively low Solubility Of [C(4)mim][Tf2N], instead, gives rise to a nearly complete segregation of the IL component on the bilayer, altering its volume, compressibility, and electrostatic environment. The computational results display important similarities to the results of recent experimental measurements for ILs in contact with phospholipid model membranes (see Evans, K. O. Int. J. Mol. Sci. 2008, 9, 498-511 and references therein).

Model calculations for copper clusters on Au(111) surfaces

Using the semi-empirical embedded-atom method, the structure of small copper clusters on Au(111) surfaces has been investigated both by static and dynamic calculations. By varying the size of roughly circular clusters, the edge energy per atom is obtained; it agrees quite well with estimates based on experimental results. Small three-dimensional clusters tend to have the shape of a pyramid, whose sides are oriented in the directions of small surface energy. The presence of a cluster is found to distort the underlying lattice of adsorbed copper atoms. (C) 2002 Published by Elsevier Science B.V.

Simulation study of Pd submonolayer films on Au(hkl) and Pt(hkl) and their relationship to underpotential deposition

The structure and stability of palladium adlayers on Au(hkl) and Pt(hkl) were studied at different coverage degrees by means of Monte Carlo simulations using the interatomic potentials of the embedded atom model. In all cases the Pd films were found to grow epitaxially and pseudomorphically with the crystallographic orientation of the substrate. The differences and similarities of the adlayer with the substrate were analyzed.