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Strong ionic interactions, as well as the consequent correlations between cation and anion dynamics, give ionic liquids various physical features that set them apart from ordinary organic solvents. In particular, they result in larger viscosities and larger densities than mixtures of neutral compounds with similar molecular structures. However, both the direct effect of electrostatic interactions and the increase of liquid density contribute to the high viscosity and so far no experimental or computational work enabled a clear quantification of those effects. Also, the effects over the shear thinning behavior, which may have important consequences for application as lubricants, were not considered yet. Here, these questions were tackled by performing non-equilibrium molecular dynamics (NEMD) simulations changing both the strength of ionic interactions and liquid density at several shear rates using a coarse grained model. The relative dielectric constant was adjusted to reproduce viscosity data from all-atoms simulations on both zero shear and high shear conditions. Elimination of ionic interactions results in a reduction of density and zero shear viscosity and also delays the beginning of shear thinning to higher shear rates. Restoring density to the ionic liquid's value only partially reverses the alterations. Correlations of the non-newtonian behavior and changes in the intermolecular structure and contact lifetimes were also explored.

Two polymerizable ionic liquids (or monomeric ionic liquids, mILs) namely 1-butyl-3-methylimidazolium and choline acrylates ([C4mim]A and ChA, respectively) were synthesized using the modified Fukumoto method from corresponding chlorides. The chemical structure of the prepared mILs was confirmed with FTIR and NMR study. Investigation of the thermal properties with DSC demonstrates that both mILs have a Tg temperature of about 180 K and a melting point around 310 K. It was shown that the temperature dependence of FTIR confirm the Tg to be below 200. Both mILs exhibited non-Newtonian shear thinning rheological behavior at shear rates >4 s−1. It was shown that [C4mim]A is able to dissolve bacterial cellulose (BC) leading to a decrease in its degree of polymerization and recrystallisation upon regeneration with water; although in the ChA, the crystalline structure and nanofibrous morphology of BC was preserved. It was demonstrated that the thixotropic and rheological properties of cellulose dispersion in ChA at room temperature makes this system a prospective ink for 3D printing with subsequent UV-curing. The 3D printed filaments based on ChA, containing 2 wt% of BC, and 1% of N,N′-methylenebisacrylamide after radical polymerization induced with 1% 2-hydroxy-2-methylpropiophenone, demonstrated Young’s modulus 7.1 ± 1.0 MPa with 1.2 ± 0.1 MPa and 40 ± 5% of strength and ultimate elongation, respectively.

Deep eutectic solvents (DESs) are similar to ionic liquids (IL) in terms of physicochemical properties and technical uses. In ILs, far-infrared (FIR) spectroscopy has been utilized to reveal ionic interactions and even to produce a signature of the strengthening of the cation-anion hydrogen bond. However, for the situation of the DES, where the mixing of a salt and a molecular species makes the interplay between multiple intermolecular interactions even more complex, a full investigation of FIR spectra is still absent. In this work, the FIR spectrum of the DES, often referred to as ethaline, which is a 1:2 mixture of choline chloride and ethylene glycol, is calculated using classical molecular dynamics (MD) simulations and compared to experimental data. To explore the induced dipole effect on the computed FIR spectrum, MD simulations were run with both nonpolarizable and polarizable models. The calculation satisfactorily reproduces the position of the peak at ∼110 cm

Binary mixtures of the ionic liquids 1-ethyl-3-methylimidazolium dicyanamide and tributyl(methyl)ammonium dicyanamide, [C2C1im]x[N4441](1-x)[N(CN)2], are studied by means of their excess properties (enthalpy and volume), their viscosity, and their Raman spectra. The mixtures exhibit positive values of excess volume VE and excess enthalpy HE. The plot of the logarithm of viscosity as a function of composition is consistent with the finding HE > 0. The excess thermodynamic properties of the ionic liquid mixtures are compared with well-known results for binary mixtures of (high-temperature) molten salts. The asymmetry of the curve HE versus composition is reproduced by considering the volumetric fraction of the [C2C1im]x[N4441](1-x)[N(CN)2] mixtures according to basic results of the theory of regular solutions. The anion totally symmetric stretching mode νs(C≡N) was used to probe the local environment around the anion in a Raman spectroscopy investigation of the [C2C1im]x[N4441](1-x)[N(CN)2] mixtures as a function of the composition. The Raman band shape (peak frequency and bandwidth) of the νs(C≡N) mode changes as expected from the fluctuation of concentration around the probe oscillator according to models for vibrational spectroscopy of liquid mixtures. This thermodynamic and spectroscopic study leads to the classification of the [C2C1im]x[N4441](1-x)[N(CN)2] mixture as a regular solution. The application of the regular solution equation for HE to other ionic liquid binary mixtures is discussed.

To assess the prevalence of temporomandibular disorder (TMD) in adolescents and estimate possible associations with poverty.A cross-sectional study nested within a prospective birth cohort study conducted in São Luís, Maranhão, Brazil.2,412 adolescents aged 18-19 years.The presence of TMD, classified according to the Fonseca Anamnestic Index, was used as the outcome. The following explanatory variables were assessed: gender, household head, paved/asphalted street, piped water, and socioeconomic background, based on the Brazilian Association of Market Research criteria and the poverty income ratio (PIR). Logistic regression analysis was performed with the estimation of odds ratios (OR) and 95% confidence intervals.TMD was common (51.4%) and was associated with poverty, as it was more frequent among adolescents from social classes D-E (OR=2.60; 95% CI: 1.48-4.55) and C (OR=1.82; 95% CI: 1.12-2.99) compared to A/B, and among poor adolescents using the PIR (OR=1.50; 95% CI: 1.02-2.33).The prevalence of TMD in socioeconomically disadvantaged adolescents in São Luís is high, and these data allow the early identification of at-risk groups. We recommend carrying out other population-based studies, using diagnostic strategies with greater accuracy.

The Raman band belonging to the totally symmetric stretching mode of the [BF4]− anion, νs(BF4), in 1-alkyl-3-methylimidazolium ionic liquids, [CnC1im][BF4], n = 4, 6, and 8, has been measured under high pressure using a diamond anvil cell. The pressure dependence of νs(BF4) frequency up to 2.0 GPa is converted to a function of density using high pressure extrapolations of equations of states as discussed in previous works. The density induced shift of the νs(BF4) frequency was calculated by a perturbed hard-sphere model by considering the probe oscillator as a pseudo-diatomic molecule. In contrast to previous findings for the stretching mode of [PF6]− in [CnC1im][PF6] ionic liquids, for which the calculation considered only the repulsive short-range forces, in the case of [CnC1im][BF4] the calculation indicates the role played by the attractive forces on the νs(BF4) frequency shift.

Poly(ionic liquid)s are an interesting class of compounds because of their unique chemical and physical properties gathering the characteristics of ionic liquids and polymers. Pressure and temperature have been demonstrated to be alternative parameters to obtain polymers from monomeric species using only physical tools. In this work, we investigate the reaction under high pressure and room temperature of the ionic liquid 1-allyl-3-methylimidazolium iodide by using the diamond anvil cell technique in combination with synchrotron X-ray diffraction and electronic and vibrational spectroscopies. The results indicate a chemical reaction happening through the terminal double bond of the allyl group both in crystalline and glassy phases with the onset of the reaction around ∼7 GPa. Vibrational spectra present evidence for an oligomerization reaction in both the phases. The reaction occurring both in glassy and crystal phases indicates a mechanism not driven by collective motions and likely related to local topological arrangements. The results presented herein extend our understanding of ionic liquid instability boundaries under high pressure and contribute to the development of alternative synthetic routes to achieve poly(ionic liquids).

A Raman spectroscopy study of 1-ethyl-3-methylimidazolium hydrogen sulfate, [C2C1im][HSO4], as a function of temperature, has been performed to reveal the role played by anion–anion hydrogen bond on the phase transitions of this ionic liquid. Anion–anion hydrogen bonding implies high viscosity, good glass-forming ability, and also moderate fragility of [C2C1im][HSO4] in comparison with other ionic liquids. Heating [C2C1im][HSO4] from the glassy phase results in cold crystallization at ∼245 K. A solid–solid transition (crystal I → crystal II) is barely discernible in calorimetric measurements at typical heating rates, but it is clearly revealed by Raman spectroscopy and X-ray diffraction. Raman spectroscopy indicates that crystal I has extended ([HSO4]−)n chains of hydrogen-bonded anions but crystal II has not. Raman spectra recorded at isothermal condition show the ultraslow dynamics of cold crystallization, solid–solid transition, and continuous melting of [C2C1im][HSO4]. A brief comparison is also provi...

A local order-disorder transition has been disclosed in the thermophysical behavior of the ionic liquid 1-benzyl-3-methylimidazolium dicyanamide, [Bzmim][N(CN)2], and its microscopic nature revealed by spectroscopic techniques. Differential scanning calorimetry and specific heat measurements show a thermal event of small enthalpy variation taking place in the range 250-260 K, which is not due to crystallization or melting. Molecular dynamic simulations and X-ray diffraction measurements have been used to discuss the segregation of domains in the liquid structure of [Bzmim][N(CN)2]. Raman and NMR spectroscopy measurements as a function of temperature indicate that the microscopic origin of the event observed in the calorimetric measurements comes from structural rearrangement involving the benzyl group. The results indicate that the characteristic structural heterogeneity allow for rearrangements within local domains implying the good glass-forming ability for the low viscosity ionic liquid [Bzmim][N(CN)2]. This work sheds light on our understanding of the microscopic origin behind complex thermal behavior of ionic liquids.

The vibrational spectra of two cyano-based ionic liquids, 1-ethyl-3-methylimidazolium dicyanamide (C 2 C 1 Im DCA) and 1-ethyl-3-methylimidazolium tricyanomethanide (C 2 C 1 Im TCM) are revisited experimentally and computationally using IR spectroscopy and ab initio molecular dynamics simulations, respectively. In the experimental spectrum of C 2 C 1 Im DCA, a number of interesting vibrational signatures are found. Aside from the expected symmetric and anti-symmetric stretching bands of the cyano groups, a Fermi resonance of a combination band and a CN stretching normal mode is identified. The assignment is confirmed by a normal mode analysis of the AIMD based IR spectrum. The AIMD does not only predict the existence of the combination band but also seems to capture the frequency shift and intensity change caused by Fermi resonance. The interpretation of the experimental C 2 C 1 Im TCM spectrum is more straightforward as no resonance effects are found. The combination of experimental spectroscopy and advanced AIMD simulations is a very promising approach to gain new insights into the behavior of room-temperature ionic liquids.

Vibrational spectroscopy has continued use as a powerful tool to characterize ionic liquids since the literature on room temperature molten salts experienced the rapid increase in number of publications in the 1990's. In the past years, infrared (IR) and Raman spectroscopies have provided insights on ionic interactions and the resulting liquid structure in ionic liquids. A large body of information is now available concerning vibrational spectra of ionic liquids made of many different combinations of anions and cations, but reviews on this literature are scarce. This review is an attempt at filling this gap. Some basic care needed while recording IR or Raman spectra of ionic liquids is explained. We have reviewed the conceptual basis of theoretical frameworks which have been used to interpret vibrational spectra of ionic liquids, helping the reader to distinguish the scope of application of different methods of calculation. Vibrational frequencies observed in IR and Raman spectra of ionic liquids based on different anions and cations are discussed and eventual disagreements between different sources are critically reviewed. The aim is that the reader can use this information while assigning vibrational spectra of an ionic liquid containing another particular combination of anions and cations. Different applications of IR and Raman spectroscopies are given for both pure ionic liquids and solutions. Further issues addressed in this review are the intermolecular vibrations that are more directly probed by the low-frequency range of IR and Raman spectra and the applications of vibrational spectroscopy in studying phase transitions of ionic liquids.

High energy X-ray diffraction has been combined with containerless techniques to determine the structure of a series of alkali and ammonium nitrate and nitrite liquids. The systems have been modelled using molecular dynamics simulation which allows for the flexibility of, and movement of charge within, the molecular anions. The model reproduces the experimentally-determined scattering functions in both the low- and high-Q regimes reflecting the inter- and intra-molecular length-scales. For ammonium nitrate the best fit to the diffraction data is obtained by assuming the NH4+ cation to have a radius closer to that for Cs+ rather than a smaller cation such as Rb+ as often previously assumed. The alkali nitrites show an emergent length scale, attributed to the nitrogen-nitrogen spatial correlations, that depends on both temperature and the identity of the alkali cation. The corresponding nitrates show a more subtle effect in the nitrogen-nitrogen correlations. As a result, the nature of this N-N length-scale appears different for the respective nitrites and nitrates.

Solubility parameters such as Hildebrand's solubility parameter or its square, the cohesive energy density ced are often not able to predict solubilities of organic compounds in ionic liquids accurately. It has been suggested that this is an effect of the structural heterogeneity that many ionic liquids exhibit due to the non-polar alkyl chains forming separate domains from the charged parts of the cation and the anion. We here calculated the partial volumes of the polar and non-polar domains in Molecular Dynamics simulations of several 1-alkyl-3-methylimidazolium nitrates and 1-octyl-3-methylimidazolium hexafluorophosphate. We used these partial volumes to calculate the ced of the polar and non-polar domains. For 1-octyl-3-methylimidazolium nitrate the internal pressures Pi of the domains were also calculated. Our results show that ced and Pi are indeed very different in the domains, and that the domains containing the hydrophobic alkyl chains have solvent parameters similar to alkanes. For the domains that contain the charged part of the ions, ced and Pi are much higher, and Pi is comparable to what is found for high temperature molten salts. The results provide a possible explanation why solubility parameters seem incorrect for many ionic liquids, and may be useful in estimating more useful values using computer simulations.

Molecular dynamics (MD) simulations of five ionic liquids based on 1-alkyl-3-methylimidazolium cations, [CnC1im]+, have been performed in order to calculate high-frequency elastic moduli and to evaluate heterogeneity of local elastic moduli. The MD simulations of [CnC1im][NO3], n = 2, 4, 6, and 8, assessed the effect of domain segregation when the alkyl chain length increases, and [C8C1im][PF6] assessed the effect of strength of anion–cation interaction. Dispersion curves of excitation energies of longitudinal and transverse acoustic, LA and TA, modes were obtained from time correlation functions of mass currents at different wavevectors. High-frequency sound velocity of LA modes depends on the alkyl chain length, but sound velocity for TA modes does not. High-frequency bulk and shear moduli, K∞ and G∞, depend on the alkyl chain length because of a density effect. Both K∞ and G∞ are strongly dependent on the anion. The calculation of local bulk and shear moduli was accomplished by performing bulk and shea...

The phase diagram of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesufonyl)imide, [Pyrr1,4][NTf2], was explored by synchroton X-ray diffraction and Raman scattering measurements as a function of temperature and pressure. Glass transition Tg(p) and melting Tm(p) temperatures were obtained from atmospheric pressure up to ca. 2.0 GPa. We found that both the Tg(p) and Tm(p) curves follow essentially the same pressure dependence. The similarity of pressure coefficients, dTg/dp ≈ dTm/dp, is explained within the non-equilibrium thermodynamics approach for the glass transition by assuming that one of the Ehrenfest equations is appropriated for Tg(p), whereas Tm(p) follows the Clausius-Clapeyron equation valid for the first-order transitions. The results highlight that ionic liquids are excellent model systems to address fundamental questions related to the glass transition.

Collective dynamics within the THz frequency range has been investigated by molecular dynamics (MD) simulations of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C 2 C 1 im][TFSI], 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, [C 2 C 1 im][FSI], and lithium solutions of Li[TFSI] and Li[FSI] in each of these liquids. We calculated time correlation functions of mass current fluctuations for longitudinal (LA) and transverse acoustic (TA) sound modes at different wave vectors, k . The dispersion curves of excitation energy, ω ( k ), calculated by MD simulations were compared with recent data for these systems reported by Fujii et al., J. Chem. Phys. 138, 151101 (2013), using inelastic X-ray scattering (IXS) spectroscopy. The reasonable agreement between experiment and simulation indicates that non-polarizable potential models for these ionic liquids provide satisfactory representation of the collective dynamics at least at high-( k , ω ) range. Even though Li + solution is more viscous than the pure ionic liquid, the high-frequency sound velocity of the solution is the same as the pure liquid.

When adjusting the pH of deposition baths, ammonia (NH 3 ) is often used instead of sodium hydroxide (NaOH), but its effects on the chemical and/or electrochemical processes are not usually considered. Here the influence of NH 3 on the deposition rate, composition and magnetic properties of amorphous cobalt-boron (CoB) alloys deposited from alkaline plating baths containing citrate is discussed. We have observed that when the pH of the solution was adjusted with NH 3 , CoB films were deposited at higher rates and the B content decreased with increasing pH. Opposite trends were observed when NaOH was used to adjust the bath pH. These observations were discussed in terms of the complex species distribution in solution and of the buffering characteristics of NH 3 . The reducing agent, dimethylaminoborane, has its electrooxidation also affected by the presence of NH 3 in solution. Amorphous, soft CoB magnetic films with coercivity values varying from 40 Oe to 80 Oe, inversely dependent on the B content of the film, were obtained.

Silicon nitride, with a permittivity mid-way between SiO 2 and common high-k materials such as HfO 2 , is widely used in microelectronics as an insulating layer on top of oxides where it serves as an impurity barrier with the positive side effect of increasing the dielectric constant of the insulator when it is SiO 2 . It is also employed as charge storage in nonvolatile memory devices thanks to its high concentration of charge traps. However, in the case of memories, it is still unclear which defects are responsible for charge trapping and what is the impact of defect concentration on the structural and electronic properties of SiN x . Indeed, for the amorphous phase the band gap was measured in the range 5.1–5.5 eV, with long tails in the density of states penetrating the gap region. It is still not clear which defects are responsible for the tails. On the other hand, the K-center defects have been associated with charge trapping, though its origin is assigned to one Si back bond. To investigate the contribution of defect states to the band edge tails and band gap states, we adopted the β phase of stoichiometric silicon nitride (β-Si 3 N 4 ) as our model material and calculated its electronic properties employing ab initio DFT/LDA simulations with self-energy correction to improve the location of defect states in the SiN x band gap through the correction of the band gap underestimation typical of DFT/LDA. We considered some important defects in SiN x , as the Si anti-site and the N vacancy with H saturation, in two defect concentrations. The location of our calculated defect levels in the band gap correlates well with the available experimental data, offering a structural explanation to the measured band edge tails and charge trapping characteristics.

We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme [L.G. Ferreira, M. Marques, L.K. Teles, Phys. Rev. B 78 (2008) 125116] to obtain corrected band gaps and band offsets. Our calculations include the spin–orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8–1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.

In this work two systems with total phase separation composed of alternated a-Si/SiO2 and a-Si/Si3N4 respectively along with silicon-rich SiOxNy films were deposited by the PECVD technique and characterized by XANES, Raman, TEM and PL techniques. The multilayers were used to analyse the effects of phase separation in the XANES and Raman spectra as well as to determine the phase contrast in TEM images in order to elucidate upon the existence of phase separation in the silicon-rich SiOxNy films and correlate it with the high photoluminescence intensity in the visible spectra region observed in the as deposited films. The results clearly indicate that the as deposited films present partial phase separation, which is crucial for the PL emission. The effect of high temperature annealing in the silicon-rich SiOxNy films is also studied, Raman and XANES results show that heat treatments promote silicon aggregation and, in some cases, crystallization strongly influencing the PL emission. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids’ polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH3CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH3CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1-alkyl-3-methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH3CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν1 (CD3 ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright c � 2010 John Wiley & Sons, Ltd.

Molecular dynamics (MD) simulations of LiCl·6H2O showed that the diffusion coefficient D, and also the structural relaxation time , follow a power law at high temperatures, D−1 ∝ (T − To)−μ, with the same experimental parameters for viscosity (To = 207 K, μ = 2.08). Decoupling between D and occurs at Tx ∼ 1.1To. High frequency acoustic excitations for the LiCl·6H2O model were obtained by the calculation of time correlation functions of mass current fluctuations. The temperature dependence of the instantaneous shear modulus, G∞(T), was considered in the shoving model for supercooled liquids [J.C. Dyre, T. Christensen, N.B. Olsen, J. Non-Cryst. Solids 352 (2006) 4635] resulting in a linear relationship log (D−1) vs. G∞/T.

The effect of adding SO2 on the structure and dynamics of 1-butyl-3-methylimidazolium bromide (BMIBr) was investigated by low-frequency Raman spectroscopy and molecular dynamics (MD) simulations. The MD simulations indicate that the long-range structure of neat BMIBr is disrupted resulting in a liquid with relatively low viscosity and high conductivity, but strong correlation of ionic motion persists in the BMIBr-SO2 mixture due to ionic pairing. Raman spectra within the 5omega200 cm(-1) range at low temperature reveal the short-time dynamics, which is consistent with the vibrational density of states calculated by MD simulations. Several time correlation functions calculated by MD simulations give further insights on the structural relaxation of BMIBr-SO2.

Polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) and the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF 6 ) have been prepared and characterized by different techniques. Coordination of the IL by the polymer occurs mainly in the amorphous phase. This finding was correlated with previous theoretical investigations of a similar model for polymer electrolytes based on poly(ethylene oxide), PEO, and IL. It has been obtained ionic conductivity σ ∼ 10 −3 S cm −1 for the polymer electrolyte with 35 wt% of IL at 100 °C. The same order of magnitude for σ was obtained by molecular dynamics simulation of PEO/IL. This work demonstrates consistency between experimental and theoretical results for polymer electrolytes containing ionic liquids.

Thermodynamics, structure, and dynamics of an ionic liquid based on a quaternary ammonium salt with ether side chain, namely, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, MOENM2E TFSI, are investigated by molecular dynamics (MD) simulations. Average density and configurational energy of simulated MOENM2E TFSI are interpreted with models that take into account empirical ionic volumes. A throughout comparison of the equilibrium structure of MOENM2E TFSI with previous results for the more common ionic liquids based on imidazolium cations is provided. Several time correlation functions are used to reveal the microscopic dynamics of MOENM2E TFSI. Structural relaxation is discussed by the calculation of simultaneous space-time correlation functions. Temperature effects on transport coefficients (diffusion, conductivity, and viscosity) are investigated. The ratio between the actual conductivity and the estimate from ionic diffusion by the Nernst-Einstein equation indicates that correlated motion of neighboring ions in MOENM2E TFSI is similar to imidazolium ionic liquids. In line with experiment, Walden plot of conductivity and viscosity indicates that simulated MOENM2E TFSI should be classified as a poor ionic liquid.

This work reports on the growth of silicon clusters within silicon oxynitride (SiO x N y ) matrices, at low temperatures, by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. The films were characterized by Fourier transform infrared spectroscopy (FTIR), soft X-ray absorption spectroscopy (XANES) measurements at the Si K-edge and photoluminescence, before and after thermal annealing at various temperatures. The XANES spectra demonstrate the presence of silicon aggregates in as-deposited and annealed films. A correlation between the presence of silicon clusters in the as-deposited samples and the intensity of the photoluminescence emission is observed.

The salt tetra(n-butyl)ammonium croconate, [(n-C4H9)4N]2C5O5⋅4H2O, (TBCR), is a very viscous glassforming liquid which undergoes a glass transition at room-temperature. Raman band shape analysis of the totally symmetric ring breathing mode of the croconate dianion, C5O52−, was performed by Fourier analysis. The vibrational time correlation functions obtained from the isotropic Raman spectra were modelled with well-known models for vibrational dephasing. The time correlation functions of pure TBCR and of TBCR in acetonitrile solutions were compared with previous results for the simple salt Li2C5O5 in aqueous solution. It has been found remarkable changes of the dynamic parameters characterizing the vibrational dephasing of C5O52− in these different environments. Discontinuous temperature dependence of the dephasing parameters was observed at the glass transition temperature of pure TBCR. In glassy TBCR, however, common models for vibrational dephasing are not strictly valid because the Raman bands display ...

Molecular dynamics (MD) simulation has been used in a detailed investigation of structure and dynamics of molten sodium chlorate, NaClO3. Results obtained with nonpolarizable and polarizable models are compared, the latter being implemented by using a fluctuating charges approach for the anions. The partial charges of the nonpolarizable model and the parameters of the polarizable model were obtained by ab initio calculations of a single ClO3− anion. The calculated static structure factor of molten NaClO3 is in good agreement with recent neutron scattering results. A detailed picture of the distribution of cations-around the anions is provided. Proper to the rather large dipole moment of the ClO3− anion, short-range dipole ordering between pair of anions is discernible in the MD simulations. The equilibrium structure of molten NaClO3 is not too affected by including polarization effects on the anions, but significant polarization effects are observed in the dynamics of the simulated system. The ionic diffusion coefficients increase by including polarization effects, so that the polarizable model gives higher conductivity and lower viscosity than the nonpolarizable model.

Molecular dynamics (MD) simulations of the glass-forming liquid Ca0.4K0.6(NO3)1.4 (CKN) have been performed at several temperatures from a liquid state at 800 K down to a glassy state at 150 K. The well-known Ewald summation method of handling the long-range electrostatic interactions has been replaced by the recently proposed method of truncated shifted Coulomb potential (Wolf; et al. J. Chem. Phys. 1999, 10, 8254). Some comparisons between dynamical properties of liquid CKN simulated with either of these methods are provided. A previously introduced polarizable fluctuating charge model (FCM) for the nitrate anion (Ribeiro, M. C. C. Phys. Rev. B 2000, 61, 3297) has been used. It is shown that the FCM is an improvement on the nonpolarizable rigid ion model (RIM) counterpart as the glass transition temperature Tg of the system simulated with the FCM is in better agreement with the experimental calorimetric value (Tg ≈ 475, 380, and 335 K for the RIM, FCM, and experiment, respectively). Reorientational time...

Molecular dynamics (MD) simulations of molten LiCl/KCl and LiF/KF mixtures at 1030 K and molar fraction x = 0.5 and also of pure components LiCl, KCl, LiF, and KF have been performed. The aim of the MD simulations was to calculate the internal mobilities of the Li+ and the K+ cations in order to reproduce the Chemla effect, that is, the strong composition dependence of the cations' internal mobilities. In line with experimental findings, it has been found by MD simulations that the isotherms of the internal mobilities of chlorides and fluorides belong to different patterns. Whereas the more usual pattern of isotherms found in the chloride mixture can be explained by simple structural and dynamical properties depending most on first-neighbor anion−cation pairs, these do not explain why a distinct pattern of isotherms is found in the fluoride mixture. Structure and structural relaxation in the simulated systems are further discussed by calculating partial static structure factors, Sαβ(k), and intermediate s...

The Chemla effect concerns the strong composition dependence of the internal ionic mobilities of cations in mixtures of two molten salts with a common anion, in which the mobility of the large cation can be higher than the small one at low concentrations of the latter. Molecular dynamics simulations of molten (Li,Cs)NO3, (Li,K)NO3, (Li,Na)NO3, (Na,Cs)NO3, each at two different compositions at a given temperature, and also pure LiNO3 and pure KNO3, have been performed with the aim of reproducing the Chemla effect. The key role played by anion polarization on the Chemla effect in molten alkali nitrates is demonstrated by comparing the calculated mobilities using nonpolarizable and polarizable models. Polarization effects were included in the simulations by using a previously proposed fluctuating charge model (FCM) for the NO3− anion. It is shown that a single potential model for a (M1,M2)NO3 mixture gives the correct composition dependence of the M1 and the M2 mobilities provided that polarization effects a...

The resonance Raman spectra of manganate(V) ion in aqueous solution in the visible and near-UV regions were studied. The maximum in the Raman excitation profile (REP) of the totally symmetric vibrational mode (ν1) at ca 600 nm is assigned to a charge-transfer transition with appreciable d–d character. Owing to marked orbital mixing in such systems, the observed Raman enhancement could also be assigned to a d–d transition with a high charge-transfer character. The absence of overtones in the Raman spectrum indicates a small shift in the equilibrium Mn—O bond distances (δr) between the excited and fundamental electronic states. This finding was confirmed by the calculation of the REP within the time formalism approach. The best fitted δr value is lower than the corresponding reported values for manganate(VII) and manganate(VI) ions. Two models were used in the calculations, in which whether a single or two electronic transitions were considered in the visible range of the absorption spectrum. Similar δr values were obtained with both models. Copyright © 1999 John Wiley & Sons, Ltd.

The fluctuating charge (FQ) model proposed by Rick et al. [(J. Chem. Phys. 101, 6141 (1994)] for molecular dynamics (MD) simulation of water is applied to a test case for polyatomic ionic systems. A system resembling alkali cyanide crystals, with two partial charges on the atomic sites of the polarizable anions, is considered. The need for charge fluctuation considerations in such a simple system is demonstrated by ab initio calculations of the partial charges in the cyanide ion with different orientations within a fixed octahedral environment of sodium ions. It is shown that the charge distributions in the crystal obtained with the FQ model are sensitive to changes in the environment in such a way that the anions become more polarizable as the lattice parameter increases. Conversely, the charge distributions shrink with increasing repulsive short-range interactions. Furthermore, a well-known polarization effect, that is, the reduction in the frequencies of longitudinal optic modes of the crystal, is also obtained with the FQ model.

A recently introduced polarizable-ion model for BeCl2 is compared to high quality ab initio calculations for the geometries of isolated chains [BeCl2] n . The relaxed geometries and vibrational frequencies (calculated using an instantaneous normal mode (INM) approach) are found to agree well. The density of states for the melt, calculated using the INMs, is shown to be very structured compared with typical molten salts, corresponding to a more ‘molecular’ spectrum. The band frequencies are seen to change little between the melt and the isolated chains further promoting the description of the liquid as an ensemble of such ‘polymeric’ chains. The calculated Raman spectrum is compared with experiment and shown to be fully consistent with the model as long as they are considered in terms of the symmetry of the molecular chains themselves. The dangers of assigning experimental bands in terms of the motions of local coordination polyhedra are emphasized.

We present a theoretical study with ab initio techniques on magnetic and electronic properties of 3d transition metal mononitrides. We perform the calculations in the wurtzite (w) and the zincblende (zb) structures, and find the tendency of all zb mononitrides to become half-metallic (HM) under hydrostatic strain. MnN, CrN, and VN become HM with integer magnetic moments of 4, 3 and 2μB, respectively. CrN shows ferromagnetism (FM) throughout the range of our lattice constant calculations, while VN is FM beyond the lattice constant of 4.65 A. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Mutations in the p53 tumour suppressor gene are found at high frequency in bladder cancer. There is strong evidence that p53 plays an important role in controlling the cell cycle after DNA damage by ionizing radiation. However, the effect of loss of p53 function on radiosensitivity is not yet clear. Radiotherapy combined with chemotherapy is the most common treatment for patients with invasive bladder cancer. Recently three bladder cancer cell lines have been established and this paper investigates the p53 status and clonogenic survival of these cell lines following irradiation. It was found that one line expresses wt p53 (UCRU-BL-13) and two lines contain a codon 72 polymorphism (UCRU-BL-17 and UCRU-BL-28). UCRU-BL-17 cells also contain a point mutation affecting codon 280. The level of p53 expression in the cell lines is clearly different, with UCRU-BL-17 expressing a higher level of p53 compared with UCRU-BL-13; UCRU-BL-28 expressed intermediate levels. The clonogenic survival of these cell lines has been determined. It was found that the line expressing a p53 mutation was more sensitive than those with wild type p53, providing support for a model in which loss of p53 function is associated with increased radiosensitivity, possibly due to reduced p53-dependent DNA repair.

The long-standing question of the nature of the low-energy transition present in the optical spectrum of azo dyes was addressed by investigating the resonance Raman spectrum of 4-(2-pyridylazo)resorcinol (PAR). The Raman spectra were obtained at different pH values where the prevailing species are the monoanionic (HL-) or the dianionic (L2-) forms. The excitation profiles and absorption spectra were calculated satisfactorily using a single excited state as responsible for the low-energy transition present in the optical spectrum. The remarkably stable Cu(II) and Zn(II) chelates involving the coordination of the HL- species to the metal ions were also investigated, and again the excitation profiles and absorption spectra were calculated satisfactorily using a single excited state. In fact, the concerted use of the transform method and time-dependent theory indicates that the displacement parameters for the metal chelates are much more similar to those obtained for the L2- species than those for HL- species. In the case of the Cu(II) chelate, a long progression of overtones and combination bands was observed, which is uncommon for such an extended chromophore. Concerning the nature of the electronic transition responsible for the resonance enhancement, the extensive electronic delocalization of the chromophore and the complex composition of the normal modes preferentially enhanced must be noted. In other words, it is expected that the ππ* and nπ* states are thoroughly mixed in this class of the molecular systems. © 1997 by John Wiley & Sons, Ltd.

The separation of the Raman correlation function as a product of independent vibrational and reorientational correlation functions is investigated. The present model is a unification of previous models which treat separately vibrational dephasing and reorientational relaxation within the context of the stochastic approach. It indicates that the so-called product approximation for the Raman correlation function can fail even when the relaxation rate is distinct for vibrational and reorientational relaxations. Application to experimental data for liquid CS2 is presented.

The time-dependent theory of the resonance Raman effect was employed for the calculation of the Raman excitation profiles and optical absorption spectra of the meial dithiolene species [Zn(dmit)2]2− and [Ni(dmit)2]2− (dmit = 4,5-dimercapto-1,3-dithiolc-2-thionc) The model adopted takes into account the three normal modes notable for their enhancement at resonance, and embodies the linear non-Condon coupling contribution. Previous calculations for these species using the transform method lead to estimates of the relative displacements of potential surface minima for the three modes considered, while the present calculations led to absolute values for such displacements. The metal-sulphur bond length is increased by 0.016 and 0.027 A in the zinc and nickel complexes, respectively.

Molecular dynamics simulations were performed for ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion, [NTf(2)], and ammonium cations with increasing length of the alkyl chain and ether functionalized chain. The signature of charge ordering is a sharp peak in the charge-charge structure factor, S(qq)(k), whose intensity is barely affected for longer carbon chain in tetraalkylammonium systems, but decreases in ether functionalized ionic liquids. The first sharp diffraction peak (FSDP) and the corresponding intermediate range order (IRO) are observed in the total S(k) of ionic liquids containing ammonium cations with relatively long chains. The intensity of the FSDP is lower in the total S(k) of the ether derivative in comparison with the tetraalkylammonium counterpart of the same chain length. It is shown that the nature of the IRO is structural heterogeneity of polar and non-polar domains, even though domains defined by chain interactions in the ether derivatives become more polar. Charge correlation in the ether derivative is modified because cations can be coordinated by oxygen atoms of the ether functionalized chain of neighboring cations.