Ion-Specific Hydration Effects: Extending the Poisson-Boltzmann Theory

In aqueous solutions, dissolved ions interact strongly with the surrounding water, thereby modifying the solution properties in an ion-specific manner. These ion-hydration interactions can be accounted for theoretically on a mean-field level by including phenomenological terms in the free energy that correspond to the most dominant ion-specific interactions. Minimizing this free energy leads to modified Poisson-Boltzmann equations with appropriate boundary conditions. Here, we review how this strategy has been used to predict some of the ways ion-specific effects can modify the forces acting within and between charged interfaces immersed in salt solutions.Comment: 11 pages, 2 figure

High Density QCD Physics with Heavy Ions in CMS

The heavy ion program of the CMS experiment will examine the QCD matter under extreme conditions, through the study of global observables and specific probes.Comment: 4 pages, Presented at Moriond QCD and Hadronic interactions, La Thuile, Italy, 23 March 200

Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements

We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material

Heavy Ion Physics at LHC

The study of heavy ion interactions constitutes an important part of the experimental program outlined for the Large Hadron Collider under construction at CERN and expected to be operational by 2006. ALICE is the single detector having the capabilities to explore at the same time most of the characteristics of high energy heavy ion interactions. Specific studies of jet quenching and quarkonia production, essentially related to $\mu$ detection are also planned by CMS.Comment: 5 pages, 1 figure (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

Ionic profiles close to dielectric discontinuities: Specific ion-surface interactions

We study, by incorporating short-range ion-surface interactions, ionic profiles of electrolyte solutions close to a non-charged interface between two dielectric media. In order to account for important correlation effects close to the interface, the ionic profiles are calculated beyond mean-field theory, using the loop expansion of the free energy. We show how it is possible to overcome the well-known deficiency of the regular loop expansion close to the dielectric jump, and treat the non-linear boundary conditions within the framework of field theory. The ionic profiles are obtained analytically to one-loop order in the free energy, and their dependence on different ion-surface interactions is investigated. The Gibbs adsorption isotherm, as well as the ionic profiles are used to calculate the surface tension, in agreement with the reverse Hofmeister series. Consequently, from the experimentally-measured surface tension, one can extract a single adhesivity parameter, which can be used within our model to quantitatively predict hard to measure ionic profiles.Comment: 14 pages, 6 figure

Long-range specific ion-ion interactions in hydrogen-bonded liquid films

Anions populate fluid interfaces specifically. Here, we report experiments showing that on hydrogen-bonded interfaces anions interact specifically over unexpectedly long distances. The composition of binary electrolyte (Na+, X−/Y−) films was investigated as a function of solvent, film thickness, and third ion additions in free-standing films produced by blowing up drops with a high-speed gas. These films soon fragment into charged sub-micrometer droplets carrying excess anions detectable in situ by online electrospray ionization mass spectrometry. We found that (1) the larger anions are enriched in the thinner (nanoscopic air-liquid-air) films produced at higher gas velocities in all (water, methanol, 2-propanol, and acetonitrile) tested solvents, (2) third ions (beginning at sub-μM levels) specifically perturb X−/Y− ratios in water and methanol but have no effect in acetonitrile or 2-propanol. Thus, among these polar organic liquids (of similar viscosities but much smaller surface tensions and dielectric permittivities than water) only on methanol do anions interact specifically over long, viz.: ⟨ri − rj⟩/nm = 150 (c/μM)^(−1/3), distances. Our findings point to the extended hydrogen-bond networks of water and methanol as likely conduits for such interactions

Formation of an unconventional Ag valence state in Ag2NiO2

The Ag ion in the recently synthesized novel material Ag2NiO2 adopts an extremely unusual valency of 1/2, leaving the Ni ion as 3+, rather than the expected 2+. Using first principles calculations, we show that this mysterious subvalent state emerges due to a strong bonding-antibonding interaction between the two Ag layers which drives the lower band beneath the O p complex, eliminating the possibility of a conventional Ag 1+ valence state. The strong renormalization of the specific heat coefficient, gamma, is likely due to strong spin fluctuations that stem from nearly complete compensation of the ferro- (metallic double exchange and the 90 degree superexchange) and antiferromagnetic (conventional superexchange via Ni-O-Ag-O-Ni path) interactions

The Scaled-Charge Additive Force Field for Amino Acid Based Ionic Liquids

Abstract. Ionic liquids (ILs) constitute an emerging field of research. New ILs are continuously introduced involving more and more organic and inorganic ions. Amino acid based ILs (AAILs) represent a specific interest due to their evolutional connection to proteins. We report a new non- polarizable force field (FF) for the eight AAILs comprising 1-ethyl-3-methylimidazolium cation and amino acid anions. The anions were obtained via deprotonation of carboxyl group. Specific cation-anion non-covalent interactions have been taken into account by computing electrostatic potential for ion pairs, in contrast to isolated ions. The van der Waals interactions have been transferred from the CHARMM36 FF with minor modifications. Therefore, compatibility between our parameters and CHARMM36 parameters is preserved. Our FF can be easily implemented using a variety of popular molecular dynamics programs. It will find broad applications in computational investigation of ILs