50 research outputs found
Field theoretic calculation of the surface tension for a model electrolyte system
We carry out the calculation of the surface tension for a model electrolyte
to first order in a cumulant expansion about a free field theory equivalent to
the Debye-H\"uckel approximation. In contrast with previous calculations, the
surface tension is calculated directly without recourse to integrating
thermodynamic relations. The system considered is a monovalent electrolyte with
a region at the interface, of width h, from which the ionic species are
excluded. In the case where the external dielectric constant epsilon_0 is
smaller than the electrolyte solution's dielectric constant epsilon we show
that the calculation at this order can be fully regularized. In the case where
h is taken to be zero the Onsager-Samaras limiting law for the excess surface
tension of dilute electrolyte solutions is recovered, with corrections coming
from a non-zero value of epsilon_0/epsilon.Comment: LaTeX, 14 pages, 3 figures, 1 tabl
Variational approach for electrolyte solutions: from dielectric interfaces to charged nanopores
A variational theory is developed to study electrolyte solutions, composed of
interacting point-like ions in a solvent, in the presence of dielectric
discontinuities and charges at the boundaries. Three important and non-linear
electrostatic effects induced by these interfaces are taken into account:
surface charge induced electrostatic field, solvation energies due to the ionic
cloud, and image charge repulsion. Our variational equations thus go beyond the
mean-field theory. The influence of salt concentration, ion valency, dielectric
jumps, and surface charge is studied in two geometries. i) A single neutral
air-water interface with an asymmetric electrolyte. A charge separation and
thus an electrostatic field gets established due to the different image charge
repulsions for coions and counterions. Both charge distributions and surface
tension are computed and compared to previous approximate calculations. For
symmetric electrolyte solutions close to a charged surface, two zones are
characterized. In the first one, with size proportional to the logarithm of the
coupling parameter, strong image forces impose a total ion exclusion, while in
the second zone the mean-field approach applies. ii) A symmetric electrolyte
confined between two dielectric interfaces as a simple model of ion rejection
from nanopores. The competition between image charge repulsion and attraction
of counterions by the membrane charge is studied. For small surface charge, the
counterion partition coefficient decreases with increasing pore size up to a
critical pore size, contrary to neutral membranes. For larger pore sizes, the
whole system behaves like a neutral pore. The prediction of the variational
method is also compared with MC simulations and a good agreement is observed.Comment: This version is accepted for publication in Phys. Rev. E
Polarizable ions at interfaces
A non-perturbative theory is presented which allows to calculate the
solvation free energy of polarizable ions near a water-vapor and water-oil
interfaces. The theory predicts that larger halogen anions are adsorbed at the
interface, while the alkali metal cations are repelled from it. The density
profiles calculated theoretically are similar to those obtained using the
molecular dynamics simulations with polarizable force fields
Ion size effects at ionic exclusion from dielectric interfaces and slit nanopores
A previously developed field-theoretic model [R.D. Coalson et al., J. Chem.
Phys. 102, 4584 (1995)] that treats core collisions and Coulomb interactions on
the same footing is investigated in order to understand ion size effects on the
partition of neutral and charged particles at planar interfaces and the ionic
selectivity of slit nanopores. We introduce a variational scheme that can go
beyond the mean-field (MF) regime and couple in a consistent way pore modified
core interactions, steric effects, electrostatic solvation and image-charge
forces, and surface charge induced electrostatic potential. We show that in the
dilute limit, the MF and the variational theories agree well with MC simulation
results, in contrast to a recent RPA method. The partition of charged Yukawa
particles at a neutral dielectric interface (e.g air-water or protein-water
interface) is investigated. It is shown that as a result of the competition
between core collisions that push the ions towards the surface, and repulsive
solvation and image forces that exclude them from the interface, a
concentration peak of finite size ions sets in close to the dielectric
interface. We also characterize the role played by the ion size on the ionic
selectivity of neutral slit nanopores. We show that the complex interplay
between electrostatic forces, excluded volume effects induced by core
collisions and steric effects leads to an unexpected reversal in the ionic
selectivity of the pore with varying pore size: while large pores exhibits a
higher conductivity for large ions, narrow pores exclude large ions more
efficiently than small ones
Accurate Determination of Ion Polarizabilities in Aqueous Solutions
We present a novel method for obtaining salt polarizabilities in aqueous solutions based on our recent theory for the refractive index of salt solutions, which predicts a linear relationship between the refractive index and the salt concentration at low concentrations, with a slope determined by the intrinsic values of the salt polarizability and the density of the solution. Here we apply this theory to determine the polarizabilities of 32 strong electrolyte salts in aqueous solutions from refractive index and density measurements. Setting Li^+ as the standard ion, we then determine the polarizabilities of seven cations (Na^+, K^+, Rb^+, Cs^+, Ca^(2+), Ba^(2+), and Sr^(2+)) and seven anions (F^–, Cl^–, Br^–, I^–, ClO_4^–, NO_3^–, and SO_4^(2–)), which can be used as important reference data. We investigate the effect of temperature on salt polarizabilities, which decreases slightly with increasing temperature. The ion polarizability is found to be proportional to the cube of bare ionic radius (r_(bare)^3) for univalent ions, but the relationship does not hold for multivalent ions. Contrary to findings of Krishnamurti, we find no significant linear relationship between ion polarizability and the square of the atomic number (N^2) for smaller ions
Dielectric constants of yttrium and rare‐earth garnets, the polarizability of gallium oxide, and the oxide additivity rule
Outcome von Kindern mit angeborenen Lungenfehlbildungen: Bericht über 6 Jahre Erfahrung in der Kinderchirurgie der Uniklinik Bonn
Die Trichterbrustkorrektur nach Nuss - Erfahrungen und Ergebnisse nach 5 Jahren und 100 Patienten
Morgagni hernia presenting with massive pericardial effusion and ascites: prenatal management by thoraco-amniotic shunting and fetal endoscopic tracheal occlusion (FETO) and review of the literature
Morgagni hernia presents a rare type of congenital diaphragmatic hernia (CDH, about 2-5 %) (Herman, J Perinatol 21:343-344, 2001), which is characterized by an anterior mainly right-sided defect of the diaphragm. Infrequently, this is combined with a herniation of the liver into the pericardial cavity (Ak,, Prenat Diagn 11:719-724, 1991; Stevens, Pediatr Radiol 26:791-793, 1996). This may cause massive pericardial effusion and subsequently lung hypoplasia (Pober et al., Congenital diaphragmatic hernia overview, University of Washington, Seattle, 2015; Ikeda, J Perinat Med 30:336-340, 2002; Hara, J Obstet Gynaecol Res 33:561-565, 2007). So far only few cases have been reported in fetal life. We report a case of Morgagni hernia with pericardiodiaphragmatic aplasia, complicated by two-compartment effusions (massive pericardial effusion and mild ascites), diagnosed in the second trimester. The case was successfully managed in utero with thoraco-amniotic shunting and late tracheal occlusion, followed by corrective surgery after birth. A review of the literature was performed, identifying 13 cases of prenatally diagnosed Morgagni hernia. The diagnosis was established by the sonographic findings of pericardial effusion und intrathoracic herniation of the liver. In only two cases a prenatal intervention was carried out. All neonates were operated postnatally with excellent final outcome