Micelle Formation in Aqueous Solutions of Room Temperature Ionic Liquids: A Molecular Dynamics Study.

1-Alkyl-3-methylimidazolium cations in the presence of water are used as a test system to study by molecular dynamics the formation of micelles in aqueous mixtures of highly anisotropic room temperature ionic liquids (IL). Structural properties, i.e., radial distribution functions (RDF) and transport parameters, such as diffusion coefficients and conductivities, are computed as a function of the IL/water mole fraction. The concentration plots reveal a sharp change of the slope of both the cation self-diffusion coefficient and the first peak of the head-head RDF at approximately the same value of the concentration. This transition, considered as a measure of a critical micellar concentration, appears only for the most anisotropic systems, composed of longer alkyl chains. The formation of the micelles is confirmed from the analysis of the tail-tail and cation-water RDFs. As a general result, we found that the larger the anisotropy of the ionic liquid the lower the critical concentration and the larger the proportion of monomers forming part of the micelles. The molecular dynamics predictions are in line with the experimental evidence reported for these systems.

The interaction between hybrid organic-inorganic halide perovskite and selective contacts in perovskite solar cells: an infrared spectroscopy study.

The interaction of hybrid organic-inorganic halide perovskite and selective contacts is crucial to get efficient, stable and hysteresis-free perovskite-based solar cells. In this report, we analyze the vibrational properties of methylammonium lead halide perovskites deposited on different substrates by infrared absorption (IR) measurements (4000-500 cm(-1)). The materials employed as substrates are not only characterized by different chemical natures (TiO2, ZnO and Al2O3), but also by different morphologies. For all of them, we have investigated the influence of these substrate properties on perovskite formation and its degradation by humidity. The effect of selective-hole contact (Spiro-OmeTad and P3HT) layers on the degradation rate by moisture has also been studied. Our IR results reveal the existence of a strong interaction between perovskite and all ZnO materials considered, evidenced by a shift of the peaks related to the N-H vibrational modes. The interaction even induces a morphological change in ZnO nanoparticles after perovskite deposition, pointing to an acid-base reaction that takes place through the NH3(+) groups of the methylammonium cation. Our IR and X-ray diffraction results also indicate that this specific interaction favors perovskite decomposition and PbI2 formation for ZnO/perovskite films subjected to humid conditions. Although no interaction is observed for TiO2, Al2O3, and the hole selective contact, the morphology and chemical nature of both contacts appear to play an important role in the rate of degradation upon exposure to moisture.

Correction: The effect of recombination under short-circuit conditions on the determination of charge transport properties in nanostructured photoelectrodes.

Correction for 'The effect of recombination under short-circuit conditions on the determination of charge transport properties in nanostructured photoelectrodes' by J. Villanueva-Cab et al., Phys. Chem. Chem. Phys., 2016, 18, 2303-2308.

The effect of recombination under short-circuit conditions on the determination of charge transport properties in nanostructured photoelectrodes.

We report on the commonly unaccounted for process of recombination under short-circuit conditions in nanostructured photoelectrodes with special attention to the charge collection efficiency. It is observed that when recombination under short circuit conditions is significant, small perturbation methods overestimate the charge-collection efficiency, which is related to the inaccurate determination of the electron diffusion coefficient and diffusion length.

Effective electrostatic interactions arising in core-shell charged microgel suspensions with added salt.

The mixture formed by charged (ionic) microgels in the presence of 1:1 added salt, with explicit consideration of a core-shell structure of the microgel particles, is studied. By solving numerically the three-component Ornstein-Zernike integral equations, the counter- and coion penetration inside the microgel network and the resulting effective microgel-microgel electrostatic interaction are calculated. This is done in the limit of very low microgel concentration, so that the resulting pair-wise effective potential is not affected by many-body particle-particle interactions. The ion-ion, microgel-ion, and microgel-microgel correlations are all treated within the Hypernetted-Chain approximation. The results obtained clearly show that the addition of salt to the microgel suspension has a deep impact on the screening of the bare charge of the particles, confirming an already well-known result: the strong reduction of the effective charge of the microgel occurring even for diluted electrolyte concentrations. We show that this effect becomes more important as we increase the shell size of the particle and derive a semi-empirical model for the effective charge as a function of the electrolyte concentration and the shell extension. The resulting microgel-microgel effective pair potential is analysed as a function of the shell extension and salt concentration. In all cases the interaction is a soft potential when particles overlap. For non-overlapping distances, our theoretical results indicate that microgel particles can be regarded as hard spherical colloids bearing an effective charge given by the net charge inside the particle and the microgel-microgel interaction shows a Yukawa-like behaviour as a function of the interparticle distance. It is also observed that increasing the bare-charge of the microgel induces a strong microgel-counterion coupling in the limit of very low electrolyte concentrations, which cannot be justified using linearized theories. This leads to an even more important adsorption of counterions inside the microgel network and to a reduction of the microgel-microgel effective repulsion.

ZnO-based dye solar cell with pure ionic-liquid electrolyte and organic sensitizer: the relevance of the dye­oxide interaction in an ionic-liquid medium.

The use of non-volatile electrolytes and fully organic dyes are key issues in the development of stable dye-sensitized solar cells (DSCs). In this work we explore the performance of ZnO-based DSCs sensitized with an indoline derivative coded D149 in the presence of a pure ionic-liquid electrolyte. Commercial nanostructured zinc oxide and an electrolyte composed of iodine plus (1) pure 1-propyl-3-methyl imidazolium iodide (PMII) and (2) a blend of PMII with low-viscosity ionic liquids were employed to construct the devices. Without further additives, the fabricated devices exhibit remarkable short-circuit photocurrents and efficiencies under AM1.5 simulated sunlight (up to 10.6 mA cm−2, 2.9% efficiency, 1 sun, active area = 0.64 cm2) due to the high surface area of the ZnO film and the high absorptivity of the D149 dye. Impedance spectroscopy is used to characterize the devices. It is found that the addition of the low-viscosity ionic-liquid improves the transport features (leading to a better photocurrent) but it does not alter the recombination rate. The robustness of the dye­oxide interaction is tested by applying continuous illumination with a Xenon-lamp. It is observed that the photocurrent is reduced at a slow rate due to desorption of the D149 sensitizer in the presence of the ionic liquid. Exploration of alternative ionic-liquid compositions or modification of the ZnO surface is therefore required to make stable devices based on ZnO and fully organic dyes.

Management of chylous fistula as a complication of neck dissection: a 10-year retrospective review.

Chylous fistula is a serious complication of neck surgery. The aim of this study was to analyse the incidence, treatment and evolution of chylous fistula in neck dissection. We conducted a retrospective study of 304 patients, 295 (97.03%) men and nine (2.97%) women. Ages ranged from 24 to 80 years (mean = 59.28 years, SD = 6.02) and they had all undergone neck dissection. Chylous fistula occurred in four cases (1.31%). Incidence was 1.83% in laryngeal cancer and 2.7% in oral cavity and oropharyngeal cancer. No statistically significant correlation was found between tumoral stage and fistula occurrence. Radiotherapy prior to surgery was a risk factor although the association was not statistically significant. The incidence rates for radical and functional neck dissection were 3.3% and 0.46%, respectively, statistically significant (P = 0.042). The fistulas were located on the left side in all cases. One of the four patients required surgical intervention and another one died. The occurrence of chylous fistula increased significantly the length of hospital stay (P = 0.01). Chylous fistulas appear on the left side, radiotherapy prior to surgery is a risk factor and there is not correlation with tumoral stage. Chylous fistulas are significantly more common in radical than in functional dissections and increase significantly the length of hospital stay.